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  • Genome-wide identification of Osmanthus fragrans bHLH transcription factors and their expression analysis in response to abiotic stress
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2020-01-18
    Yuli Li; Ling Li; Wenjie Ding; Haiyan Li; Tingting Shi; Xiulian Yang; Lianggui Wang; Yuanzheng Yue

    Sweet osmanthus (Osmanthus fragrans) is a widely used evergreen aromatic ornamental tree with poor tolerance to low temperatures. The basic helix-loop-helix (bHLH) transcription factor protein family, which is the second largest protein family in plants, has been found to play essential roles in the response to multiple abiotic and biotic stresses, especially cold stress. However, the bHLH gene family in sweet osmanthus has not yet been analyzed. In this study, 206 OfbHLH genes, which were classified into 25 subfamilies, were successfully identified from recently released whole-genome sequence data. Segmental duplication events had contributed mainly to the expansion of the OfbHLH gene family and all these duplicated gene pairs had experienced purifying selection. The transcriptome data exhibited different expression levels of OfbHLH genes in various tissues. Quantitative real-time PCR results indicated that the expression patterns of most IIIb, III(d + e), IVc, IX, and XII subfamilies could be up- or down-regulated under cold stress, and, among them, IIIb, III(d + e), and part of the XII subfamily participated in the response to multiple abiotic stresses. Six candidate OfbHLH genes (OfbHLH120/128/133/163/164/191), which were significantly up- or down-regulated during the cold stress process, were identified. Further studies indicated that OfbHLH120/128/163 had transcriptional activation activity and were located in the nucleus, implying that these genes are involved in the regulation of expression of cold tolerance genes. This study provides a solid foundation for the functional analysis of the OfbHLH gene family members involved in cold stress response and could be useful in the breeding of sweet osmanthus with improved cold tolerance.

    更新日期:2020-01-21
  • Early season precipitation accounts for the variability of fine-root traits in a Tibetan alpine grassland
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2020-01-18
    Jirong Cao; Li Lin; Shuang Pang; Xiaowei Guo; Guangmin Cao; Jin-Sheng He; Qibing Wang

    Root trait dynamics can reflect the adjustment in the strategy of plant roots in resource acquisition and energy storage when responding to climatic fluctuations. Under global change, the responses of root traits in climate sensitive ecosystems, e.g. high-elevation and cold Alpine ecosystems, remain unclear. To identify how climatic fluctuations drive the variations in the root traits in a Tibetan alpine grassland, we intensively investigated the temporal dynamic of root traits by biweekly measuring root length, root biomass and specific root length for three continuous years. The SRL showed strong seasonal patterns across three years, which did not support SRL considered as a constant in previous root system modeling, while as hypothesized, mean SRL in non-growing seasons was significantly higher than that in growing seasons by 17 %. The accumulative air temperature of growing or non-growing season exerted synchronic effects on the changes in root traits. Nevertheless, precipitation was observed to have the lag effects on root traits, showing that January-April accumulative precipitation was a major driver for the variations in the root length and root biomass respectively peaking in July and June each year. Distinguishingly, root length relied on the lag effect of precipitation; however, for root biomass, the continuous accumulative precipitation together with peak month, i.e. the January-June accumulative precipitation, was also significantly vital. Our results would have an important implication for predicting responses of belowground carbon cycling to global climate change.

    更新日期:2020-01-21
  • MdATG8i functions positively in apple salt tolerance by maintaining photosynthetic ability and increasing the accumulation of arginine and polyamines
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2020-01-17
    Liuqing Huo; Zijian Guo; Ping Wang; Zhijun Zhang; Xin Jia; Yiming Sun; Xun Sun; Xiaoqing Gong; Fengwang Ma

    Autophagy has been widely reported to play critical roles in plant adaption to various abiotic and biotic stressors. Although many studies have shown that autophagy-deficient mutants exhibit sensitivity to salt stress, our understanding of the detailed function of autophagy in response to salt stress remains limited. In this study, we found that the expression of MdATG8i was induced by salt stress. We treated transgenic apple plants overexpressing MdATG8i with salt stress, and explored its biological role in response to salt treatment. The results showed that the growth limitation, reactive oxygen species generation and Na+ accumulation caused by salt stress were alleviated in transgenic plants. The shrinkage of stomata and the damage to photosynthetic ability caused by salt stress were differentially mitigated. These changes were accompanied by the elevated autophagic activity and the accumulation of proline, arginine and its downstream polyamine products in two transgenic lines, which play important roles in plant tolerance to salt stress. In summary, these results revealed that MdATG8i-mediated autophagy enhanced salt tolerance in apple, primarily by alleviating the decrease in carbon assimilation and the accumulation of compatible osmolytes.

    更新日期:2020-01-17
  • Freeze-thaw events delay spring budburst and leaf expansion while longer photoperiods have opposite effect under different [CO2] in white birch: advance it under elevated but delay it under ambient [CO2]
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2020-01-13
    Binyam Tedla; Qing-Lai Dang; Sahari Inoue

    Past studies indicate that narrower conduits such as those in diffuse-porous species are less vulnerable to freeze-thaw (FT) induced embolism and also facilitate the refilling of embolized xylem conduits early in the spring, resulting in an earlier bud break. In this study, we investigated if a novel environmental condition associated with climate change-induced northward migration will affect the vulnerability to FT-induced embolism and spring phenology in white birch. Seedlings were grown under ambient (400 μmol mol−1) or elevated CO2 concentration (1000 μmol mol−1), and four photoperiod regimes corresponding to 48 (seed origin), 52, 55, and 58 °N latitude. We found that the longest photoperiod (corresponding to 58 °N latitude) significantly increased the maximum specific hydraulic conductivity of the stem. CO2 concentration ([CO2]) and photoperiod had no significant impact on the vulnerability to FT-induced embolism. The treatment of 5 freeze-thaw cycles (+5 to −20 °C) led to an 11% loss of hydraulic conductivity in dormant seedlings that had been stored at −4 °C for 3 months while the effect of such a treatment in the fall was much smaller. This result suggests that freeze-thaw events in late winter or spring can impair the hydraulic conductivity of the xylem which in turn may negatively affect the physiology of the trees. Indeed, the FT treatment in this study delayed budburst and leaf expansion in the spring. It is interesting to note that photoperiods had the opposite effect on budburst under different [CO2]: longer photoperiods led to earlier budburst in the spring under elevated [CO2], but delayed budburst under ambient [CO2]. The synergistic effect of longer photoperiods and CO2 elevation suggests that the growing season for white birch may be longer than what we predict from either factor alone at a migration site in the future when [CO2] will be much higher.

    更新日期:2020-01-13
  • Spatial variation patterns of plant herbaceous community response to warming along latitudinal and altitudinal gradients in mountainous forests of the Loess Plateau, China
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2020-01-13
    Manhou Xu; Xiaoli Li; Min Liu; Ying Shi; Huakun Zhou; Baogui Zhang; Jialiang Yan

    As climate warming is more obvious in high mountains, the spatial patterns of mountainous vegetation responding to climate warming are expected to become a new aspect in forest ecosystem research. However, we do not know how spatial patterns of vegetation in mountainous regions respond to climate warming, and we also do not know what will happen to the patterns when rainfall occurs. Here, we conducted warming experiments to explore the variation pattern of the response of the herbaceous community to experimental warming along latitudinal and altitudinal gradients in mountainous forests of the Loess Plateau. In low and high warming amplitudes, air temperature increased by a maximum of 0.86 °C and 2.83 °C, respectively; the response of air temperature was obviously affected by elevation, whereas air humidity was not sensitive to warming. When rainfall occurred, warming produced decreases in soil temperature by a maximum of 0.56 °C and 0.61 °C in low and high warming amplitudes, respectively; soil temperature was evidently affected by latitude; and soil moisture was insensitive to warming. That was, the corresponding responsiveness of air and soil temperature was dependent on elevation and latitude, and a sudden increase in soil moisture caused by rainfall influenced the effects of warming on soil temperature. Warming also increased plant height and coverage, but plant density and frequency did not respond to warming, thus leading to insignificant changes for importance values of grass, sedge, and forb. Moreover, plant richness and Simpson indices increased in low-amplitude warming and decreased in high-amplitude warming, but the Pielou index was insensitive to warming. The responsiveness of these plant factors decreased with latitude and increased with elevation. Correlations tended to be enhanced by warming among vegetation, temperature (air temperature and soil temperature), and moisture (air humidity and soil moisture); the correlation among vegetation, air humidity, and soil moisture increased relatively rapidly in response to warming. With soil moisture increasing, plant height diminished and species diversity enlarged in warming, demonstrating that moisture increase caused by rainfall modified warming effects on vegetation. In regions with water deficits as the Loess Plateau, warming reinforced the relationship of vegetation with water and thus promoted its dependence on water. Warming could be controlled in a certain range and thus exerted positive effects on vegetation and facilitated plant community development. In regions where water is the limiting factor, warming effects were largely influenced by rainfall; the moisture increment induced by rainfall might weaken warming effects on soil and its correlation with vegetation.

    更新日期:2020-01-13
  • Waterlogging tolerance of five soybean genotypes through different physiological and biochemical mechanisms
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2020-01-09
    Natália Garcia; Cristiane Jovelina da-Silva; Kassia Luiza Teixeira Cocco; Darwin Pomagualli; Fabiane Kletke de Oliveira; João Victor Lemos da Silva; Ana Cláudia Barneche de Oliveira; Luciano do Amarante

    Waterlogging is a serious environmental threat that limits crop growth and yield in low-lying, rainfed areas in many regions across the globe. Here we investigated the effects of waterlogging and subsequent re-oxygenation on the physiology and biochemistry of three soybean [Glycine max (L.) Merrill] genotypes (PELBR10-6000, PELBR11-6028, and PELBR11-6042) and two cultivars (TEC IRGA 6070 and BMX Potência). Plants were grown under greenhouse conditions until the V4 stage when they were subjected to waterlogging for seven days. The water was then drained and plants were allowed to recover for another seven days. Overall, all genotypes suppressed waterlogging stress with distinct mechanisms. Waterlogged PELBR10-6000 surpassed control plant levels of CO2 assimilation rate and readily responded to the energy lack induced by hypoxia by activating the fermentative enzymes and alanine aminotransferase. Similar mechanisms were observed in BMX Potência, which restored metabolism to control levels at the end of the recovery. PELBR11-6028 and PELBR11-6042 activated the antioxidant defenses, and TEC IRGA 6070 did not delay flowering.

    更新日期:2020-01-09
  • Unraveling the complexities underlying sulfur deficiency and starvation in the cyanobacterium Anabaena sp. PCC 7120
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-12-31
    Surbhi Kharwar; Arun Kumar Mishra

    The present study focuses to decipher the impact of long-term sulfur deficiency in the cyanobacterium Anabaena sp. PCC 7120. Cell growth parameters (cell biomass and photopigments) were analysed under varying long-term sulfur deficiency showed significant reduction in growth under sulfur limitations. The reminiscent growth of cyanobacterium in the sulfur shortage possibly pertained to minimize cell size and spherical cell shape. Additionally, lower sulfur availability exhibited negative impacts on photopigments, D1 protein (all3572) transcription and PSII efficiency in the cyanobacterium. Furthermore, depletion in protein and corresponding increase in carbohydrate and lipid contents were interpreted as reprogrammed C-allocation. Additionally, enzyme assay of ATP sulfurylase depicted increased activity in the deficient conditions. Moreover, decreased intracellular concentrations of Mg2+, Fe2+, Ca2+, Na+, and K+ at low sulfur supplementations might be a consequence of counter-ion balancing and attributed to lipid peroxidation and electrolyte leakage resulted from increased ROS. In addition, overexpression of desC followed by fatty acid unsaturation and programmed cell death markers were also noticed. Overall, the result suggest that reduced biomass in sulfur limitation is a cumulative outcome of disrupted photosynthesis, reprogrammed C-allocation, reduced electrolyte contents, and subsequent PCD in the cells of Anabaena sp. PCC 7120 reveal S deficiency exerts an adverse impact on cyanobacterial population and reduces primary productivity.

    更新日期:2019-12-31
  • Phototropin is partly involved in blue-light-mediated stem elongation, flower initiation, and leaf expansion: A comparison of phenotypic responses between wild Arabidopsis and its phototropin mutants
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-12-20
    Yun Kong; Youbin Zheng

    Our previous study on bedding plants indicated that blue light in association with low phytochrome activity, relative to red light, can promote elongation growth as one of the shade-avoidance responses. We hypothesized that phototropin is involved in the blue light promotion effects. To test the hypothesis, plant growth and morphology were examined in wild Arabidopsis (Col-0), and its three phototropin-deficient mutants (phot1, phot2, and phot1phot2) under four light quality treatments: (1) R, pure red light (660 nm); (2) B, pure blue light (455 nm); (3) BR, unpure blue light created by mixing B with low-level (6%) R; and (4) BRF, unpure blue light created by adding low-level far-red light (735 nm) to BR with red/far-red ≈ 1. Continuous (24-h) light-emitting diode lighting with 100 μmol m−2·s−1 photosynthetic photon flux density, and an air temperature of ≈ 23 ℃ were used with the above treatments. The calculated phytochrome photoequilibrium, an indicator of phytochrome activity, was 0.89, 0.69, 0.50, and 0.60 for R, BR, B, and BRF, respectively. After 20 days of light treatments, for the wild-type plants, B or BRF, compared to R or BR, promoted stem elongation, plant flowering, and leaf expansion, showing typical shade-avoidance responses. However, for the phototropin mutants, the promotion effects of B or BRF, relative to R or BR, on the above plant traits were reduced. In the absence of the phototropin(s), plants had reduced stem elongation and delayed flower initiation under B or BRF rather than R or BR, or reduced leaf expansion to a larger degree under B or BRF than R or BR. Our results suggest that phototropin is partly involved in the promotion of stem elongation, plant flowering, and leaf expansion mediated by blue light in association with low phytochrome activity.

    更新日期:2019-12-20
  • Transcriptomic analysis of Glycine soja and G. max seedlings and functional characterization of GsGSTU24 and GsGSTU42 genes under submergence stress
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-12-12
    Xiaojiang Li; Ying Wang; Feng Liu; Boyi Pi; Tuanjie Zhao; Bingjun Yu

    The plant-specific tau-class of glutathione S-transferase (GSTU) has high stress-inducing expression characteristics that can play an important protective role in plant tolerance to different environmental stresses. To explore the mechanisms underlying submergence and reoxygenation tolerance in soybean plants, the transcriptomic analysis of leaves under submergence was firstly performed using the highly submergence-tolerant G. soja accession (P18B) and the submergence-sensitive G. max cultivar (KF1), and two potential submergence-responsive GSTU genes, GsGSTU24 and GsGSTU42, were identified. Their physiological functions in tolerance to submergence and subsequent desubmergence were compared in GsGSTU24- and GsGSTU42-overexpressing hairy root composite soybean plants or transgenic Arabidopsis plants. The results showed that, overexpression of GsGSTU24 or GsGSTU42 could alleviate submergence and subsequent desubmergence stress on soybean hairy root composite plants or transgenic A. thaliana seedlings by enhancing antioxidant ability for leaf ROS detoxification or homeostasis reestablishment, and by improving the chlorophyll content and quantum efficiency of chlorophyll fluorescence (Fv/Fm) for maintenance of leaf photosynthetic capacity. Our results further indicate that, the genes GsGSTU42 or GsGSTU24 from high submergence-tolerant G. soja P18B could be considered as the vital submergence tolerance determinants for utilization in molecular breeding designs for flooding-tolerant crop improvement in the future.

    更新日期:2019-12-13
  • Yield-related phenotypic traits of drought resistant maize genotypes
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-12-11
    Mateus Vilela Pires, Evaristo Mauro de Castro, Bethânia Silva Morais de Freitas, Jean Marcel Souza Lira, Paulo Cesar Magalhães, Marcio Paulo Pereira

    The aim of this study was to evaluate two maize genotypes with contrasting drought-resistant phenotypic traits and to characterize how the plastic phenotypic traits contribute to yield potential under drought. The maize genotypes DKB 390 and BRS 1010 present contrasting yield traits in relation to drought and were treated with two water regimes: well-watered plant (WW, ≈ ̶ 2 kpa) and water deficit (WD, ≈ ̶ 100 kpa). In WD conditions, DKB 390 had a greater capacity to accumulate biomass in shoots than BRS 1010, indicating that shoot traits are important in increasing yield gain in the DKB 390 drought tolerant genotype and therefore, an important phenotypic trait for breeding for high yield in drought conditions. However, neither the total root dry mass nor its ratio to the shoot was related to increased yield. A large reduction in gas exchange and increased water use efficiency was observed in BRS 1010 compared to DKB 390. These traits are likely related to yield loss mainly due to decreased transpiration rate and stomatal conductance, which led to low photosynthetic rates and reduced growth. The root angle between genotypes was a constitutive trait and can be primarily responsible for the differences in yield. However, this trait in the DKB 390 genotype was affected by WD, as indicated by narrowing of the root angle. Our work describes the relationship between the narrow root growth angle in DKB 390 and its association with an increased capacity for water uptake in deeper regions, which may result in higher yield. Regarding leaf anatomy we hypothesized that both osmotic adjustment and cell wall properties can influence anisotropic cell expansion under WD conditions and result in leaf tissue with higher yield potential in DKB 390. The high plasticity of vascular tissues and wide vessels could indicate a greater propensity for embolism and a slower response to WD, leading to yield loss in BRS 1010. The results of the phenotypic plasticity of maize genotypes show a negative relationship between high plasticity and yield potential and suggest that high plasticity can result in higher yield potential only when are present in phenotypic traits responsible for higher water uptake and drought tolerance.

    更新日期:2019-12-11
  • Tomato WRKY81 acts as a negative regulator for drought tolerance by modulating guard cell H2O2–mediated stomatal closure
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-12-11
    Golam Jalal Ahammed, Xin Li, Youxin Yang, Chaochao Liu, Guozhi Zhou, Hongjian Wan, Yuan Cheng

    WRKY transcription factors (TFs) are key regulators in numerous plant biological processes and responses to stresses. Although a group III tomato WRKY, SlWKRY81, is induced by some biotic stressors, its role in drought response remains largely unknown. Here, we unveiled a critical role of SlWKRY81 in regulation of drought response by using agronomic, bioinformatics, genetic and pharmacological approaches. Drought gradually increased the transcript levels of SlWRKY81 and impaired leaf water potential and membrane stability in tomato. Analysis of plant phenotypes revealed that silencing of SlWRKY81 in tomato enhanced tolerance to drought, while its overexpression in Arabidopsis resulted in an opposite phenotype. Notably, the enhanced drought tolerance in SlWRKY81-silenced tomato plants was closely associated with a rapid and increased stomatal closure. Furthermore, such stomatal response in the SlWRKY81-silenced plants was sensitive to abscisic acid alongside drought-induced enhanced accumulation of H2O2 in the guard cells. The results suggest that SlWRKY81 acts as a negative regulator of stomatal closure by suppressing SlRBOH1-derived H2O2 accumulation, which attenuates plant tolerance to drought. These results may have potential implications on improving plant drought tolerance through genetic manipulation.

    更新日期:2019-12-11
  • H2O2 and NO are involved in trehalose-regulated oxidative stress tolerance in cold-stressed tomato plants
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-12-11
    Tao Liu, Xueling Ye, Meng Li, Jianming Li, Hongyan Qi, Xiaohui Hu

    Cold adversely affects tomato (Solanum lycopersicum) growth and yield during winter and early spring in northern China. Trehalose (Tre) is a growth regulator that is widely used to enhance plant stress tolerance. However, there are few reports on the mechanistic role of Tre in regulating tomato cold tolerance or the interactions between hydrogen peroxide (H2O2) and nitric oxide (NO) in Tre-induced cold stress tolerance in plants. Here, we explored the role of Tre in tomato cold tolerance and evaluated whether H2O2 and NO were involved in this regulation. Tre pretreatment significantly upregulated superoxide dismutase (Cu/Zn SOD) and glutathione reductase (GR1) transcription and increased catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) activities under normal temperatures. Under cold stress, Tre pretreatment dramatically elevated Cu/Zn SOD and CAT1 transcription and increased SOD and CAT activities. Tre pretreatment reduced membrane lipid peroxidation and alleviated plant growth inhibition caused by cold stress conditions. Under normal temperatures, Tre pretreatment upregulated the expression of respiratory burst oxidase homolog1 (RBOH1), nitrate reductase (NR), and nitric oxide synthase (NOS) and elevated H2O2 and NO levels. Treating tomato leaves with H2O2 and NO scavengers [dimethylthiourea (DMTU) and 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), respectively] significantly diminished Tre-mediated alleviation of membrane lipid peroxidation. The effect of H2O2 on reducing cold stress-induced damage in tomato was essentially abolished by cPTIO treatment. These results indicated that exogenous Tre enhanced cold stress tolerance in tomato by regulating the antioxidant defense system. Tre may act as an exogenous inducer of H2O2 and NO that regulate antioxidase gene expression and activities to promote plant responses to cold stress, enhance cold stress tolerance, and reduce membrane lipid peroxidation and cellular injury. NO may act downstream of H2O2 to mediate Tre-regulated tomato oxidative stress tolerance under cold stress.

    更新日期:2019-12-11
  • Buds of “Italia melhorada” grapevines grown under tropical conditions develop a quiescent state
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-11-29
    Débora Dantas, Ricardo Bressan-Smith, Ximena Noriega, Francisco J. Pérez

    A double cropping system for the grapevine (Vitis vinifera L) has been commercially adopted for use in regions where the tropical climate is characterized by high temperatures and small variations in daylength throughout the year. Under these climatic conditions, the use of hydrogen cyanamide (HC), a compound that breaks bud dormancy, is mandatory to produce homogeneous budbreak. However, it is unknown whether grapevine buds are capable of developing endodormancy (ED) under these climatic conditions. In this study, typical signals of ED, such as the number of nodes per cane, the development of periderm and the thickening of the cell wall of the bud meristematic cells, were analysed in vines of “Italia melhorada” grown in Mossoró, Brazil (5º12’16”S ), under a natural (ND) photoperiod (12/12 h), a short-day (SD) photoperiod (10/14 h) and a long-day (LD) photoperiod (14/10 h). The abundance of phytochrome A (VvPHYA) and B (VvPHYB) and FLOWERING LOCUS T (VvFT) transcripts in the leaves and buds was also determined. The results showed a reduced number of nodes per cane and development of the periderm in the shoots of grapevines grown under ND and SD photoperiods. In addition, compared with that under the LD photoperiod, the expression of VvPHYA and VvFT under the ND and SD-photoperiod decreased, and the expression of VvPHYB increased. However, the thickness of the cell wall of the bud meristematic cells increased only in the grapevines exposed to the SD photoperiod. Therefore, we hypothesize that cell wall thickening is a characteristic of ED, while decreased expression of VvPHYA and VvFT and increased expression of VvPHYB are characteristic of quiescence. Consequently, under a tropical conditions, the grapevine buds would be in a quiescent state and not in a dormant state.

    更新日期:2019-11-30
  • Expression analysis of aquaporin genes in Saussurea involucrata rosette leaves and functional analysis of upregulated SiPIP1;5A under low-temperature stress
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-11-27
    Jin Li, Wenwen Xia, Huixin Zang, Biao Dai, Yao Zhang, Yujie Feng, Aiying Wang, Zhongping Lin, Hailiang Liu, Jianbo Zhu

    Aquaporin proteins (AQPs), which are distributed in distinct membranes and function in the transport of water across cell membranes, are important for the water balance of plants in general, and especially for low-temperature adaptation. The expression of AQP genes in Saussurea involucrata (Kar. et Kir), which is highly tolerant to chilling and freezing stresses, should be distinctive from that of other cold-sensitive plants. Six tonoplast intrinsic protein (TIP) and eight plasma membrane intrinsic protein (PIP) genes were identified in S. involucrata. Among these, three TIPs and five PIPs were upregulated at a freezing temperature and SiPIP1;5B was upregulated only under chilling stress. Moreover, the expression profiles of AQP genes under chilling stress differed from those under freezing stress. The effects of light on AQP gene expression were maintained under both chilling and freezing stresses. Furthermore, the effect of light on the expression of different AQP genes differed under freezing stress between cases with and without cold acclimation. Specifically, the effect of light on SiPIP2;2 and SiPIP2;4B expression was abolished when no cold acclimation was performed. Functional analysis of SiPIP1;5A showed that its overexpression enhanced the low-temperature tolerance of tomato. We concluded that the upregulation of AQPs promoted the cold adaptation of S. involucrata. This research provides a preliminary foundation for understanding the tolerance to low temperature achieved through regulating the cell water balance.

    更新日期:2019-11-28
  • Polyploidy-mediated divergent light-harvesting and photoprotection strategies under temperature stress in a Mediterranean carnation complex
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-11-27
    Javier López-Jurado, Francisco Balao, Enrique Mateos-Naranjo

    Polyploidy can induce physiological novelties with adaptive potential, which may influence the range of environmental conditions that a neopolyploid tolerates. Dianthus broteri (Caryophyllaceae) is an autopolyploid complex that comprises four ploidy levels (2×, 4×, 6× and 12×) with separate distributions in the Iberian Peninsula, occupying different ecological niches along a gradient of temperature and aridity. We designed an experimental approach to disentangle the differential photochemical responses to temperature (from -3 °C to 53 °C) among D. broteri cytotypes by the measurement of leaf chlorophyll fluorescence. Our results showed higher energy fluxes, Fv/Fm and delayed fluorescence values along low and mild temperature levels in lower ploidies (2× and 4×) compared to higher ones (6× and 12×). This pattern would allow lower cytotypes to enhance their photosynthetic apparatus functionality in environmentally non-stressful habitats as those they inhabit. Contrarily, the 6× cytotype exhibited the overall lowest energy fluxes based on a reduced absorption while maximizing its flux ratios. Moreover, the 12× cytotype had notably high dissipation fluxes to ensure photoprotection, maintaining low but constant photochemical efficiency. These latter strategies would cause the reduction of photosynthetic capacities but help higher ploidies to tolerate the semi-arid Mediterranean environmental conditions with high temperatures under which they live.

    更新日期:2019-11-28
  • Ectopic over-expression of ABA-responsive Chickpea galactinol synthase (CaGolS) gene results in improved tolerance to dehydration stress by modulating ROS scavenging
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-11-27
    Name: Prafull Salvi, Nitin Uttam Kamble, Manoj Majee

    Galactinol synthase (EC: 2.4.1.123) is a crucial enzyme of raffinose family oligosaccharides (RFO’s) biosynthesis, essentially catalyzes the first crucial step in the raffinose biosynthetic pathway. Galactinol and raffinose accumulation along with its higher homologs such as stachyose and verbascose has been considered to participate in plant abiotic stress tolerance. Previously, we reported the function of chickpea galactinol synthase (CaGolS) genes in seed vigor and heat and oxidative stress tolerance. Here, we demonstrate the role and regulation of CaGolS in response to dehydration stress in chickpea. Though transcript accumulation and promoter-gus analyses, we demonstrate that the expression of CaGolS1 and CaGolS2 are positively influenced by dehydration stress and ABA treatment. Further, we have shown that the level of galactinol and raffinose are remarkably enhanced in response to dehydration stress and ABA. Utilizing CaGolS1 and CaGolS2 over-expression Arabidopsis lines, we demonstrate the role of CaGolS in dehydration stress tolerance. The biochemical and physiological analysis revealed that CaGolS over-expressing transgenic lines exhibited improved phenotype with respect to higher number of siliques, plant height, and rosette diameter under dehydration stress. The improved dehydration stress tolerance was corelated with higher chlorophyll retention and relative water content of transgenic lines. Further, lower H2O2, MDA content, and ion-leakage in transgenic lines suggest that CaGolS mediates dehydration stress tolerance by protecting the membrane damage from ROS attack. Collectively, our data highlight the prospect of CaGolS genes in improving dehydration stress tolerance in plants.

    更新日期:2019-11-28
  • Comparative adaptive strategies of old and young leaves to alkali-stress in hexaploid wheat
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-11-23
    Chaoxia Xiao, Xiulin Cui, Huiying Lu, Lei Han, Sibei Liu, Yuxin Zheng, Huan Wang, Hao Wang, Chunwu Yang

    Alkali stress is an important limiting factor for agricultural production. The aim of this study was to investigate whether old and young leaves have different biochemical responses to alkali stress in hexaploid wheat, and to provide molecular dissection of these differential responses on the basis of proteomic profiling. Under alkali stress, hexaploid wheat accumulated higher concentrations of Na+ in older leaves to protect young leaves. Young leaves accumulated amino acids, carbohydrates, and dehydrin proteins to relieve Na+ toxicity. Under alkali stress, 14-3-3 protein abundance was enhanced in old leaves to accelerate Na+ compartmentation in the vacuole. Abundances of 27 ribosomal proteins were significantly decreased in old leaves but not in young leaves, and many proteinases and ribonucleases also were significantly upregulated by alkali stress in old leaves. Interestingly, one E3 ubiquitin-protein ligase, one ubiquitin protein, and one proteasome protein were simultaneously upregulated in old leaves but not in young leaves. We propose that during the response to alkali stress, old leaves may programmatically degrade ribosomes through the ubiquitin-proteasome pathway to generate amino acids, which will increase tissue tolerance. Alkali stress induced remarkable enhancement of almost all free amino acids and ribose contents in old leaves, thus supporting this hypothesis. In addition, we observed that, for some salinity-tolerant protein-triads, the A, B, and D homoeologous proteins showed different response to alkali stress. This suggests that alkali stress may influence the translation of homoeologous genes, resulting in imbalanced translation of A, B, and D homoeologous genes in some gene triads.

    更新日期:2019-11-26
  • Physiological acclimation of a grass species occurs during sustained but not repeated drought events
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-11-22
    Rebecca K. Vandegeer, David T. Tissue, Susan E. Hartley, Gaétan Glauser, Scott N. Johnson
    更新日期:2019-11-22
  • Comparison and perspective of conventional and LED lighting for photobiology and industry applications
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-11-21
    Bo-Sen Wu, Yasmeen Hitti, Sarah MacPherson, Valérie Orsat, Mark G. Lefsrud

    A vast interest in plant photobiological responses is growing in both academia and commercial sectors, due to rapid developments in electrical lighting technology. Each lighting technology has its own advantages and corresponding applications, as well as disadvantages. The advantages of light emitting diodes (LEDs) have been reviewed extensively, supporting them as suitable lighting sources to investigate plant photobiological responses. However, conventional lighting sources possess some properties that cannot be met by LEDs. In this work, we provide a different perspective when considering electrical lighting system applications in plant photobiology, including wavelength availability, longevity, spectral reliability, and light uniformity. Optical and electrical components are addressed with respect to both laboratory use and greenhouse operations. The latest research findings on how different lighting sources (spectral compositions) influence the physiology of plants are presented, and current challenges for LED technology with respect to plant photobiology are discussed. Electrical lighting systems benefit the plant photobiology field in numerous ways, but comprehensive knowledge of external environment factors is required, rather than choosing the latest lighting technology.

    更新日期:2019-11-22
  • Shade pretreatment enhanced drought resistance of soybean
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-11-21
    Muhammad Ahsan Asghar, Junbo Du, Hengke Jiang, Yan Li, Xin Sun, Jing Shang, Jiang Liu, Weiguo Liu, Shakeel Imran, Nasir Iqbal, Bushra Ahmad, Sajad Hussain, Liang Yu, Chunyan Liu, Wenyu Yang
    更新日期:2019-11-22
  • ‘Endangered living fossils’ (ELFs): Long-term survivors through periods of dramatic climate change
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-11-21
    Pablo Vargas, Pedro Jiménez-Mejías, Mario Fernández-Mazuecos

    Geography and climate have been the main drivers of evolution in recent geological epochs. While new lineages of species have been formed in the last millions of years (speciation) and others have vanished as a result of historical climate changes (extinction), some ancient lineages appear to have persisted to the present day without net diversification. In this paper, evolution of ancient lineages is addressed by combining phylogenetic and conservation approaches to test the concept of ‘endangered living fossil’ (ELF). Using endangered, monospecific genera as starting point, we propose three criteria to identify ELFs (in order): (1) scarcity and narrow distribution of populations, i.e. the species (and thus the genus) is categorised as either ‘endangered’ or ‘critically endangered’ using IUCN criteria; (2) evolutionary distinctiveness, i.e. phylogenetic singularity of a single-species lineage as a result of a null net diversification rate; (iii) ancient divergence, i.e. split from the closest extant relatives predating the dramatic climate changes of particular geological epochs (specifically changes since the Miocene-Pliocene boundary). The vascular flora of the Iberian Peninsula offers a suitable study system to reliably test the ELF concept. Indeed, time-calibrated phylogenies revealed that five of the six critically endangered, monospecific genera endemic to the Iberian Peninsula are ELFs. These five genera appear to have diverged from their closest relatives in the Oligocene (Gyrocaryum), Miocene (Avellara, Castrilanthemum, Gadoria) and around the Miocene-Pliocene boundary (Naufraga). This result entails long-term survival (with no net diversification) through at least three dramatic climate changes: the Messinian Salinity Crisis (late Miocene), the establishment of the mediterranean climate (Pliocene), and the glacial-interglacial cycles (Pleistocene). Using results from the literature, we found examples of ELFs for the mediterranean floras of California (Dodecahema), Chile (Avellanita, Gomortega, Legrandia) and other Mediterranean areas of Europe (Petagnaea, Phitosia). ELFs are unique and threatened lineages representing an exceptional evolutionary heritage, and therefore they should be prioritised in biodiversity research and conservation programs.

    更新日期:2019-11-21
  • Root transcriptome analysis of Saccharum spontaneum uncovers key genes and pathways in response to low-temperature stress
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-11-17
    S. Dharshini, Nam V. Hoang, C. Mahadevaiah, T.S. Sarath Padmanabhan, G. Alagarasan, G.S. Suresha, Ravinder Kumar, Minturam Meena, Bakshi Ram, C. Appunu

    Low-temperature (LT) stress is known to restrain sugarcane productivity in sub-tropical regions significantly. Many researchers have prioritized their work towards developing climate-resilient sugarcane varieties incorporating genome of stress-tolerant sugarcane related wild-type species in the pre-breeding programs. However, the lack of genomic resources for wild-type sugarcane limits the identification and utilization of stress-related genes in molecular breeding. In this study, for the first time, we generated ∼182 million RNA-seq paired-end reads for Saccharum spontaneum roots grown under low temperature (10 °C) at different time intervals (0 h, 3 h, 6 h, 12 h, 24 h, and 48 h), to identify LT stress responsive genes and pathways. These data were assembled into 141,409 unigenes and subsequently used to identify 2715 upregulated and 1710 downregulated transcripts under LT stress. Combining evidences from GO enrichment, KEGG pathways, histological studies, biochemical assays, and physiological analysis, our results revealed several key genes and pathways involved in cold acclimatization in the S. spontaneum roots. Transcription profiling of roots during LT stress revealed cold stress sensors (i.e., proline, MDA, calcium-dependent kinase, G-coupled proteins, and histidine kinase) that trigger and activate signal transduction through transcription factors (i.e., MYB, ERF, ARF2, DREB, CAMTA, and C2H2) resulting in upregulation of LT stress responsive genes (i.e, annexin, LEA, germins, LT dehydrins, osmotins, and COR) thereby enhancing cold tolerance. Also, transcriptomic analysis envisaged cold responsive metabolic pathways such as phenylpropanoid and sugar metabolism stimulate the synthesis of flavonoid, sucrose, galactose, raffinose, and fructose, antioxidants, phytohormones, and secondary metabolites, and thus trigger cold-responsive transcriptional regulation. Together, this study provides insights into cold tolerance of wild sugarcane roots to LT stress, thus providing a foundation for developing climate-resilient sugarcane varieties.

    更新日期:2019-11-18
  • An ecological history of the relict genetic lineage of Arabidopsis thaliana
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-06-28
    Bernardo Toledo, Arnald Marcer, Belén Méndez-Vigo, Carlos Alonso-Blanco, F. Xavier Picó

    The combination of extensive population sampling with whole-genome sequencing in the annual plant Arabidopsis thaliana has recently allowed the identification of a genetically differentiated relict lineage. The most important nuclei of relict A. thaliana is found in the Iberian Peninsula and North Africa, although relict accessions have also been found scattered across Atlantic oceanic islands, eastern Mediterranean Basin, South and East Africa and China. We hypothesised that relict A. thaliana long survived and adapted to a wide array of environments in the Iberian Peninsula and North Africa due to the fact that the region repeatedly acted as glacial refugia. Given the lack of evidence to support this hypothesis, we addressed this issue by studying the ecological history of Iberian and North African relict A. thaliana. To this end, we analysed the relationship between the current habitat suitability of relict A. thaliana, estimated with species distribution models, and the vegetation dynamics in the region over the last millennia using pollen fossil data from sediment cores and reconstructions of past distribution ranges of the most important tree species occurring in the region. Overall, our results indicated that a higher current habitat suitability of relict A. thaliana was correlated with more stable vegetation dynamics since the Last Glacial Maximum and during the Holocene. Given that relict A. thaliana is known to harbour genetic variation specific to its relict nature, we also evaluated the differentiation between relict and non-relict A. thaliana accessions at the functional genetic level for the known flowering genes, CRY2 and TSF. Genomic surveys detected the existence of haplogroups of these genes occurring at very high frequency only among relict accessions. Overall, our study reinforced the relict character of this lineage thought to be at the base of the species' early history. We stress the need to sample in depth other geographic areas harbouring relict A. thaliana and conduct further functional genetic analyses between relict and non-relict accessions to keep disentangling the evolutionary trajectory of this annual plant.

    更新日期:2019-11-18
  • Leaf gas exchange and stable carbon isotope composition of redbay and avocado trees in response to laurel wilt or drought stress
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-11-11
    Raiza Castillo-Argaez, Bruce Schaffer, Aime Vazquez, Leonel D.S.L. Sternberg

    Symptoms of laurel wilt, a vascular plant disease caused by the fungus Raffaelea lauricola, are similar to those of drought stress. We compared physiological responses of redbay and avocado trees infected with laurel wilt to responses of trees with drought stress. Trees were either inoculated with R. lauricola, subjected to drought stress, or irrigated daily and not inoculated (non-stressed, control). Disease symptoms, net CO2 assimilation (A), stomatal conductance of water vapor (gs), substomatal CO2 concentration (Ci), intrinsic water use efficiency (WUEi), leaf chlorophyll index (LCI), the ratio variable to maximum leaf chlorophyll fluorescence (Fv/Fm), leaf nitrogen (N) concentration, and the ratio of 13C to 12C (δ13C) in leaves were determined prior to inoculation and the imposition of drought stress and when plants showed moderate to severe stress symptoms. Laurel wilt-infected and drought-stressed trees of each species had lower A, and gs and higher Ci, Fv/Fm, and LCI than non-stressed trees. Redbay trees with laurel wilt had significantly higher (less negative) leaf δ13C values than non-stressed trees, whereas no significant differences were found in leaf δ13C values among avocado treatments. In avocado trees with laurel wilt, there was a negative linear correlation between δ13C values and Ci but no significant correlation between δ13C values and leaf N in the inoculated trees. Inhibition of photosynthesis in avocado and redbay infected with laurel wilt was determined to be a result of the both stomatal and biochemical factors.

    更新日期:2019-11-13
  • Pretreatment with Trichoderma harzianum alleviates waterlogging-induced growth alterations in tomato seedlings by modulating physiological, biochemical, and molecular mechanisms
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-11-11
    Amr A. Elkelish, Haifa Abdulaziz S. Alhaithloul, Sameer H. Qari, Mona H. Soliman, Mirza Hasanuzzaman

    We studied the role of Trichoderma harzianum (TH) in improving the physiological, biochemical, hormonal, and molecular parameters of tomato seedlings grown under waterlogging (WL, for 14 and 28 days).pretreated with. Pretreatment with TH significantly improved the growth of tomato by enhancing the chlorophyll synthesis and uptake of essential ions, including nitrogen, phosphorus, and potassium. A reduction in anthocyanin content was also ameliorated significantly by TH pretreatment. TH significantly mitigated the WL-induced decline in height and in fresh and dry biomass accumulation. Accumulation of proline, flavonoids, anthocyanin, sugars, and soluble protein, increased with TH pretreatment. At both growth periods (14 and 28 days after treatment [DAT]), the accumulation of secondary metabolites, including total phenols and flavonoids, and the redox components (tocopherols) was increased significantly by TH pretreatment. Increased synthesis of metabolites maintained the antioxidant status of tomato, resulting in amelioration of WL-induced oxidative effects on membranes. WL and TH treatments significantly increased ethylene production and decreased abscisic acid content at both growth periods. The accumulation of reactive oxygen species, like hydrogen peroxide, in TH treated seedlings was correlated with the upregulation of the Fe-SOD gene. WL stress triggered the activity of sucrose synthase (SUS), lactate dehydrogenase (LDH), and pyruvate decarboxylase (PDC), which reached a maximum at 14 DAT, and TH pretreatment resulted in further enhancement above control and WL-stressed levels. Quantitative RT-PCR revealed differential expression of genes, where Fe-SOD and ADH were upregulated due to TH treatment and ARE, ACO, ERF, and aquaporin were downregulated relative to control plants. Pretreatment of tomato seedlings with TH improved tolerance to WL by maintaining the antioxidant status, sugar metabolism, and expression of critical genes. These results suggest that TH pretreatment is an effective way to improve WL tolerance in tomato at vegetative stage.

    更新日期:2019-11-13
  • Hydrophobic cell-wall barriers and vacuolar sequestration of Na+ ions are among the key mechanisms conferring high salinity tolerance in a biofuel tree species, Pongamia pinnata L. pierre
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-11-11
    Sureshbabu Marriboina, Attipalli Ramachandra Reddy

    Gradual soil-salinization is enhancing the proportion of non-arable salinized land areas. Developing strategies to utilize salinized lands for balanced economical productivity are highly desirable. Salt-tolerating Pongamia pinnata has gained significant attraction as a potential biofuel tree species and hence, could act as an efficient energy- crop alternative for cultivation in salinized lands. However, mechanisms conferring salt-tolerance to Pongamia are not yet demonstrated. It is highly crucial to understand the tolerance mechanisms for future breeding purposes for enhanced productivity under saline conditions. Hydroponically grown 30 days old seedlings of Pongamia are treated with two different salt concentrations (300 and 500 mM NaCl) for 8 days and analysed at regular intervals of 1, 4 and 8 days after salt exposure. Physiological parameters were recorded using infrared gas analyser and portable mini-PAM. Ion (Na+, K+, Cl―, and Ca2+) accumulation in leaves and roots were analysed through atomic absorption spectroscopy and Na+ localization was tracked through confocal laser scanning microscopy. Histochemical detection of lignin and suberin depositions in leaves and roots were carried out. Pongamia roots act as ultra-filters/strong barriers to avoid accumulation of excess Na+ levels in the leaves. The Na+ probe fluorescence analysis demonstrated effective vacuolar sequestration of Na+ in the roots. Formation of suberized multiseriate exodermis in the roots, along with extensive lignification maximized water permeability in both leaves and the roots. The present study clearly demonstrates the key cellular mechanisms conferring salinity tolerance in P. pinnata, which can be sustainably grown in salinized marginal lands as a potential biofuel tree species.

    更新日期:2019-11-13
  • Arbuscular mycorrhizal fungi alter carbohydrate distribution and amino acid accumulation in Medicago truncatula under lead stress
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-11-11
    Xiangyu Zhang, Huijuan Zhang, Yongxin Zhang, Yaqin Liu, Haoqiang Zhang, Ming Tang

    This study aims to understand the effect of arbuscular mycorrhizal (AM) inoculation on the regulation of carbon and nitrogen metabolites in Medicago truncatula plants under lead (Pb) stress. Root morphology, nutrient, photosynthesis, sucrose cleaving enzymes, the transcription levels of sucrose transporters, and metabolite profiling were evaluated via a two-factor (AM inoculation and Pb stress) pot experiment. AM inoculation alleviated the damage caused by Pb to photosynthesis and increased phosphorus uptake. AM inoculation decreased the shoot sucrose content but increased root sucrose content. The transcription of MtSUT1-1 and MtSUT4-1 in roots was upregulated by AM inoculation, which indicates that AM plant has a higher ability of sucrose transport. Both Pb stress and AM inoculation stimulated the activity of acid invertase and sucrose synthetase in roots. In shoots, minor amino acids such as cysteine were increased by AM inoculation. Sucrose content was negatively related to asparagine content. Therefore, AM inoculation may alleviate Pb toxicity by promoting the transport of sucrose from shoot to root, promoting the cleaving of sucrose in roots, and increasing minor amino acids accumulation.

    更新日期:2019-11-13
  • Desiccation Avoidance and Drought Tolerance Strategies in Bermudagrasses
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-11-11
    Krishna B. Katuwal, Brian Schwartz, David Jespersen

    The objective of this study was to characterize and compare mechanisms of drought avoidance and tolerance, specifically rooting characteristics, osmotic adjustment and antioxidant metabolism among different bermudagrasses. Six different bermudagrasses (‘Celebration’, ‘Tifway’, ‘TifTuf’, ‘UGB-70’, ‘UGB-42’ and ‘UGB-208’) were grown in field and growth chamber conditions and exposed to drought treatments. A range of drought performance was observed across bermudagrass genotypes with TifTuf being only the genotype to maintain a minimum acceptable turf quality rating of 6 at the end of drought treatments under field conditions. Along with TifTuf, UGB-42 and UGB-70 performed well in terms of percent green cover, normalized difference vegetation index (NDVI), leaf water status and membrane stability in both field and growth chamber conditions indicating these three genotypes had the best drought performance in the current study. Drought tolerant bermudagrasses were able to better maintain photosynthesis and transpiration after being exposed to drought. TifTuf had 15, 27 and 200% greater osmotic adjustment (OA) compared to poor performing Celebration in 2017 and 2018 field, and grown chamber experiments, respectively. Antioxidant enzyme activities, including activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), peroxidase (POD), catalase (CAT) and glutathione reductase (GR), were mostly greater in drought-tolerant bermudagrasses. Greater antioxidant activities reduced formation of damaging H2O2 and lipid peroxidation in TifTuf, UGB-42 and UGB-70. TifTuf had 25% greater total dry weight partitioned to roots compared to poorer performing UGB-208. Root viability was the greatest in UGB-42 and root length density (RLD) were greater in UGB-42 and UGB-70 compared to many other bermudagrasses. Results indicated better drought performances of bermudagrasses could be attributed both drought tolerance (particularly OA and antioxidant mechanisms) and desiccation avoidance (total dry weight partitioned to roots and root viability) traits.

    更新日期:2019-11-13
  • Parthenium avoids drought: understanding the morphological and physiological responses of the invasive herb Parthenium hysterophorus to progressive water stress
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-11-11
    Blair W. Cowie, Marcus J. Byrne, Ed T.F. Witkowski, Lorraine W. Strathie, Jeremy M. Goodall, Nic Venter

    Parthenium hysterophorus L. is a noxious annual invasive herb which threatens biodiversity, food security and human and animal health in various tropical and sub-tropical regions globally. Given that these regions, including South Africa, experience frequent drought events, it is important that the invasive potential of this weed be better understood in the context of water stress. This study aimed to assess the physiological and morphological responses of P. hysterophorus to water stress. To elicit these responses, juvenile and adult plants were progressively water stressed over a six-week period. Despite significant reductions in leaf water potential, relative leaf water content and stomatal conductance from severe soil water stress, plants maintained positive net photosynthesis, albeit at a severely reduced rate. Concomitantly, water-use efficiency of P. hysterophorus increased by more than 300%. Morphologically, water-stressed plants exhibited reductions in leaf area and leaf number, with adults accelerating flower production when compared to well-watered plants. Linked to this, were alterations in biomass, with juveniles and adults reducing above-ground biomass by 75% and 35%, respectively. Overall, many of the physiological and morphological responses are indicative of a largely drought avoidance strategy, allowing P. hysterophorus to persist during periods of water-stress as leafy basal rosettes (juveniles) or as reproductive herbs (adults). This research yielded valuable insights into the underlying water relations of P. hysterophorus, and how these may relate to the potential spread, detriment and management of the weed in various sub-tropical environments.

    更新日期:2019-11-13
  • Increasing level of abiotic and biotic stress on Kinnow fruit quality at different ecological zones in climate change scenario
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-11-09
    Rab Nawaz, Nadeem Akhtar Abbasi, Ishfaq Ahmad Hafiz, Azeem Khalid

    The quality of Kinnow fruit was assessed in different ecological zones by selecting three main districts: Sargodha, Toba Tek Singh (TTS) and Vehari; all of them have varying environmental conditions. Abiotic and biotic stress on fruit quality was assessed. More growing degree days, photothermal index, photo and helio thermal units were computed in Vehari, while hydrothermal units and energy use efficiency were recorded in higher values at TTS. Fruit diameter was measured from April to December and recorded with increased width in TTS and Vehari during May and June. In May, more fruit drop was noted in TTS and Vehari compared to Sargodha due to heat stress. Pests such as citrus thrips, mites and fruit fly infected fruits were recorded in higher percentage at Vehari and TTS, while citrus red scale infestation was seen more in Sargodha. In Sargodha, a higher incidence of citrus scab and melanose was noted on Kinnow fruits, while more stem-end rot infected fruits were recorded at TTS and Vehari. In abiotic stress, more wind scares were noted at Sargodha, followed by TTS, whereas stem injury and styler-end deformity were found to be non-significant. Fruit physical parameters such as width, fresh weight and peel thickness were noted more in TTS and Vehari, while more surface smoothness and firmness were observed in Sargodha. Biochemical properties such as pH, total soluble solids, titratable acidity, sugars, ascorbic acid, total dissolved salts and electrical conductivity showed higher levels in Sargodha than TTS and Vehari. More antioxidant and total anthocyanins were found in Sargodha, while higher levels of total phenolic contents were estimated at TTS and total flavonoids in Vehari. Kinnow fruit of Sargodha received more sensory scores in organoleptic evaluation. Higher percentage of A-grade fruits was harvested from Sargodha and B-grade fruits from TTS and Vehari. More numbers of fruits and weight were obtained from TTS, followed by Sargodha. Extreme events such as heat stress and smog were seen more in Vehari and TTS and subsequently their fruit quality was found to be inferior.

    更新日期:2019-11-11
  • Functional characterization of Mitogen-Activated Protein Kinase Kinase (MAPKK) gene in Halophytic Salicornia europaea against salt stress
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-11-09
    Nazia Rehman, Muhammad Ramzan Khan, Zaheer Abbas, Raja Sheraz Rafique, Madiha Zaynab, Muhammad Qasim, Sabahat Noor, Safeena Inam, Ghulam Muhammad Ali

    Mitogen-activated protein kinase (MAPK) cascade is conserved in eukaryotic organisms and plays a crucial role in signal transduction pathways, related to biotic and abiotic stress responses. The current study was aimed to target at cloning, structural and functional characterization of 1023bp SeMAPKK gene from Salicornia europaea. A SeMAPKK polypeptide chain of 340aa has eleven sub-domains, and S/TXXXXXS/T residues are conserved in the activation loop site between VII-VIII sub-domains. We identified TVY and MEY motifs at N-terminus and LKY, CAY and SKY motifs at C-terminus. Phylogenetic relationship revealed that SeMAPKK belongs to group D. Highest transcript signals were recorded in 0.75 M salt level stress, and down-regulation was observed in 1.0 M salt concentration. Overexpression of SeMAPKK gene in Arabidopsis conferred salt tolerance. Results of different salt tolerance assays revealed that transgenic plants were more tolerant and exhibited better growth than non-transgenic plants under salt stress.

    更新日期:2019-11-11
  • Sucrose plays key role in amelioration of arsenic induced phytotoxicity through modulating phosphate and silicon transporters, physiological and biochemical responses in C3 (Oryza sativa L.) and C4 (Zea mays L.)
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-11-08
    Ambedkar Gautam, Navin Kumar, Arvind Kumar Dubey, Ruma Ranjan, Nayan Sahu, Soumit Kumar Behera, Kavita Shah, Rudra Deo Tripathi, Shekhar Mallick

    Sucrose is a precursor for several vital biomolecules and essential for growth of the plant. The present study investigated the interrelationship between sucrose (25 μM) and PO4 (iP) in amelioration of arsenic (As) [60 μM of AsIII and AsV] toxicity in C3 (Oryza sativa) and C4 (Zea mays) plants. Application of sucrose recovered the iAs induced phytotoxicity, morphological and physiological parameters in both C3 and C4 seedlings. Alternatively, As accumulation enhanced the endogenous level of sucrose in the seedlings. Also, sucrose suppressed the gene expression of low silicon transporters in both C3 and C4 plants, resulting in lower iAs uptake. Presence of iP, suppressed expression of root iP transporters which coincided with reduced iAs accumulation in maize root (23%) over its AsIII, and that in shoots of both of C3 (12%) and C4 (35%) seedlings over AsV. However, the iP transporters in rice [OsPT-1, 6 & 9] and in maize (ZmPHT1;6, ZmPHT2;1, ZmPHT1;1), shoot and root, respectively, were upregulated with sucrose application, enhancing the iP accumulation. Sucrose application reduced the level of H2O2 and TBARS in both plants, while enhanced the thiolic compounds (GSH, cysteine and NPSH) and activities of antioxidant enzymes (APX, GPX and SOD) against iAs toxicity under both available and iP deprived conditions. The physiological parameters such as A, PhiPS2, gs and qP recovered whereas, NPQ was reduced with sucrose application towards iAs treatments in both the seedlings. Overall, the results indicate that sucrose plays a vital role in the amelioration of iAs induced toxicity through modulation of iP and low silicon transporters, resulting in reducing the iAs accumulation, physiological parameters and antioxidants.

    更新日期:2019-11-08
  • Cumulative effects of drought–flood abrupt alternation on the photosynthetic characteristics of rice
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-10-16
    Rui Zhu, Fengyan Wu, Shan Zhou, Tiesong Hu, Jie Huang, Yun Gao

    The photosynthetic characteristics of crops under drought–flood abrupt alternation (DFAA) provide a foundation for the precise modeling of yield formation. However, current modeling practices are largely based on single water stress conditions or continuously well-watered conditions that differs considerably from the actual rice growing conditions in South China where DFAA occurs. This study aims to investigate the cumulative effects of DFAA on the photosynthetic characteristics of rice. The experiments were conducted in 2017 and 2018, and six DFAA groups with different combinations of drought and flooding were tested during the jointing–heading stage of rice. Three additional treatments were also used to compare the photosynthetic characteristics of rice under different water conditions, namely, those under continuous well-watered (CW), continuous drought (CD), and continuous flooded (CF) conditions. The results showed that there was photosynthetic inhibition after the DFAA stress, followed by recovery and compensation. Interestingly, two different kinds of interaction between the prior drought and the subsequent flooding were observed: the antagonistic effect of the preceding drought on the subsequent-flood-induced photosynthetic inhibition and the synergistic effect of the subsequent flooding on the preceding-drought-induced photosynthetic inhibition. In addition, the antagonistic effect on gs was more pronounced in DFAA groups that experienced prior mild or long-term drought, and the synergistic effect on gs was more deleterious in DFAA groups with severe subsequent flooding. These cumulative effects of DFAA were affected by the leaf-to-air vapor pressure difference (VPDleaf) and probably resulted in different leaf water use strategies in rice. This research increases our knowledge of the effects of the interaction between drought and flooding on rice photosynthesis and highlights the need to consider these complex interactions in future yield modeling and production practices.

    更新日期:2019-11-08
  • Environmental explanation of maize specific leaf area under varying water stress regimes
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-11-07
    Huailin Zhou, Guangsheng Zhou, Qijin He, Li Zhou, Yuhe Ji, Mengzi Zhou
    更新日期:2019-11-08
  • Local adaptation along a sharp rainfall gradient occurs in a native Patagonian grass, Festuca pallescens, regardless of extensive gene flow
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-11-06
    Aldana S. López, Dardo R. López, Gonzalo Caballé, Guillermo L. Siffredi, Paula Marchelli

    Increasing global aridity combined with changing environmental conditions might cause irreparable alterations in arid and semiarid ecosystems. Knowledge of within-species genetic diversity and adaptive responses, especially along climatic gradients, becomes critical to inform management, conservation and restoration efforts. We combine the analysis of neutral (microsatellites) and adaptive divergence (morphological traits in common garden experiments) between populations along a sharp precipitation gradient in the native Patagonian grass Festuca pallescens, to disentangle patterns of local adaptation and genetic diversity. The identification of genetically based traits under divergent selection denoted the existence of local adaptation in spite of extensive gene flow. Two plant growth patterns were detected associated with two ecological regions. In arid environments, a trade-off between not resigning foliage production, and reducing the exposure to drying agents resulted in a compacted plant architecture; while in dry-sub humid environments, populations exhibited a wide architecture to cope with rainfall and radiation interception. Increasing aridity and grazing might favor a compact plant architecture, and fragmentation might reduce genetic diversity across these environments. Being a widely distributed species, F. pallescens is an excellent model species to study adaptive responses across environmental gradients facing climate change predictions, especially in dryland rangelands that maintain multiple ecosystem functions.

    更新日期:2019-11-07
  • Physiological seed dormancy increases at high altitude in Pyrenean saxifrage (Saxifraga longifolia Lapeyr.)
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-11-05
    Alba Cotado, Maria Begoña Garcia, Sergi Munné-Bosch

    Seed dormancy determines population dynamics and it is an essential feature of the ecology of high-mountain plants. Although altitudinal changes in the ecological and physiological performance of Pyrenean saxifrage (Saxifraga longifolia Lapeyr.) has been investigated to some extent, nothing it still know about how seed dormancy is influenced by environmental conditions imposed by altitude in these plants. Here, we evaluated altitudinal changes in seed viability and germination, but also on the endogenous contents of phytohormones and antioxidants in Pyrenean saxifrage. We found that, despite seed germination decreased at the highest population (2,100 m a.s.l.) relative to the other two populations (at 570 and 1,100 m a.s.l.), the highest population showed the highest seed viability, thus indicating increased seed dormancy. Hormonal profiling of the seeds revealed that this dormancy was modulated physiologically, in particular by increased abscisic acid accumulation, while gibberellin contents kept constant, relative to the seeds of the other two populations. Furthermore, seed xanthophyll contents, in particular those of lutein, neoxanthin, violaxanthin and antheraxanthin increased with altitude, while those of α-tocopherol kept unaltered. We conclude that the lower temperature imposed by altitude strongly influences not only seed viability and germination, but also seed dormancy, and that changes associated to temperature differences among populations are modulated at the physiological level by increasing the accumulation of abscisic acid and xantophylls in mature seeds. Results strongly support the contention that physiological seed dormancy has evolved as a means to increase plant survival under harsh environmental conditions in Pyrenean saxifrage plants growing in their natural habitat.

    更新日期:2019-11-06
  • Comparative analysis of maize root sRNA transcriptome unveils the regulatory roles of miRNAs in submergence stress response mechanism
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-11-05
    Ikbal Azahar, Supriya Ghosh, Ayan Adhikari, Sinchan Adhikari, Doyel Roy, Arun K. Shaw, Kashmir Singh, Zahed Hossain
    更新日期:2019-11-06
  • Genome-wide investigation of regulatory roles of lncRNAs in response to heat and drought stress in Brassica juncea (Indian mustard)
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-11-05
    Garima Bhatia, Aman Singh, Deepika Verma, Shailesh Sharma, Kashmir Singh

    Long non-coding RNAs are in general described as transcripts >200 nt and lacking potential to code for proteins. In the present study, 7613 putative lncRNAs were identified in Brassica juncea genome using in silico approaches. Of these, 1614 lncRNAs were found to be differentially expressed in response to heat and drought stress conditions. Further, we characterized these lncRNAs and performed functional annotation based on co-expression analysis strategy and pathways enrichment analysis. On these bases, the identified abiotic stress-responsive lncRNAs were found to be associated with important pathways including both enzymatic and non-enzymatic antioxidants such as glutathione metabolism, phenylpropanoid biosynthesis, cysteine metabolism, etc. Moreover, lncRNAs were also found to co-express with transcription factors associated with abiotic stress response. Finally, those lncRNAs were identified that could act as putative targets and endogenous target mimics of miRNAs involved in response to heat and drought. Further investigation could be carried out for select lncRNA candidates like those for which quantitative polymerase chain reaction analysis was performed in this study or for those which were estimated as promising modulators of stress response based on miRNA-lncRNA interaction studies. Overall, our study highlights the potential role of lncRNAs in B. juncea in response to both heat and drought stress and can help elucidate the mechanism of tolerance to these abiotic stress conditions in the oil seed crop.

    更新日期:2019-11-06
  • Aluminum toxicity-induced pollen tube growth inhibition in apple (Malus domestica) is mediated by interrupting calcium dynamics and modification of cell wall components
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-11-03
    Fang Kefeng, Xie Pengxue, Zhang Qing, Xing Yu, Cao Qingqin, Qin Ling

    Aluminum (Al) is known the most abundant metal in the Earth’s crust which is a major problem limiting crop production and yield throughout the world. Al could inhibit pollen tube elongation, however the mechanism is largely unknown. The aim of this study was to investigate the influence of Al toxicity on Malus domestica pollen tube growth and possible cytological mechanism. The results showed that Al inhibited pollen germination and tube growth in a concentration dependent manner. An non-invasive ion-selective electrode technique together with fluorescent labeling indicated that Al toxicity decreased pollen tube apex calcium influx and disrupted [Ca2+]c gradient. Al toxicity also altered actin filament orientation. Results from immuno-localization and fluorescence labeling indicated that Al toxicity affected the accumulation and distribution of callose, acid pectins, esterified pectins and arabinogalactan proteins in pollen tubes, which were supported by Fourier-transform infrared analysis. In a word, Al induced a series of the cellular toxic changes concerning calcium influx, [Ca2+]c gradient, actin and cell wall components. Based on the information provided in this article, it is concluded that Al toxicity inhibits apical growth of pollen tubes by changing calcium influx and [Ca2+]c and cell wall components.

    更新日期:2019-11-04
  • Different photoprotection strategies for mid- and late-successional dominant tree species in a high-light environment in summer
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-11-02
    Zheng-Chao Yu, Xiao-Ting Zheng, Wei-Lin, Ming-Lin Cai, Qi-Lei, Zhang, Chang-Lian Peng

    Light adaptability is a major driver of succession and evolution in natural forest plant communities. However, the relationship between plants and light is contradictory; light provides energy for plant growth, but excessive light negatively affects plant growth. To reveal the pattern of plant adaptation to diurnal variation in light, photoprotection strategies were analyzed in young and mature leaves of six dominant species at two successional stages. Mature leaves of both mid- and late-successional dominant species exhibited a higher net photosynthetic rate (Pn) than young leaves. In particular, the mature leaves of the mid-successional tree species had higher high-light tolerance because of a higher Pn, water use efficiency (WUE) and electron transfer rate (ETR). In contrast, the mature leaves of the late-successional tree species had a higher restoration ability after high-light stress because of higher thermal energy dissipation and faster stomatal regulation. Young leaves of both the mid- and late-successional dominant species exhibited a higher photoprotection capability than mature leaves. The young leaves of the mid-successional tree species had higher high-light tolerance because of their highest WUE and anthocyanin/chlorophyll (Anth/Chl) and higher flavonoid/chlorophyll (Flav/Chl), total phenolics/chlorophyll (Phen/Chl) and total antioxidant capacity/chlorophyll (TAC/Chl) ratios. The young leaves of the late-successional tree species had a stronger restoration ability due to highest Flav/Chl, Phen/Chl, and TAC/Chl ratios and a higher moisture content and non-photochemical quenching coefficient (qN, NPQ). This study shows that in a high-light environment, when leaves are at the same developmental stage, mid-successional tree species better tolerate high-light, while late-successional tree species have a greater restoration ability after high-light stress.

    更新日期:2019-11-04
  • Mycorrhizal symbiosis induces divergent patterns of transport and partitioning of Cd and Zn in Populus trichocarpa
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-11-02
    Vinicius Henrique De Oliveira, Ihsan Ullah, Jim M. Dunwell, Mark Tibbett

    We investigated how arbuscular mycorrhizal symbiosis can alter trace element uptake, distribution and toxicity in plants by examining some of the molecular mechanisms behind Populus trichocarpa tolerance to Cd and Zn, and the effects of AMF in metal homeostasis. Plants were grown under Cd and Zn contamination, with and without Rhizophagus irregularis inoculation. We determined organ metal concentrations, the expression of genes involved in trace element homeostasis, and the function of metallothionein PtMT2b by heterologous expression in yeast. P. trichocarpa was highly tolerant to both elements, with AMF increasing Zn accumulation. AMF altered the partitioning of Cd, but maintained the same patterns for Zn, indicating that despite being geochemically similar and carried mostly by the same transporters, the nutrient metal (Zn) is handled differently from the non-essential metal (Cd). High Zn and Cd down-regulated PtHMA4 (roots), and up-regulated PtZIP1 (leaves), suggesting their involvement in transporting both metals in poplar. PtMT2b was highly up-regulated in mycorrhizal roots and enhanced Cd tolerance in transformed yeast. R. irregularis reduced Cd transfer to poplar shoots, but did not affect Zn partitioning. The gene expression patterns observed offer a glimpse into the mechanisms behind trace element uptake/translocation dynamic in poplars, influenced by AMF symbiosis.

    更新日期:2019-11-04
  • Arbuscular mycorrhizas modulate root polyamine metabolism to enhance drought tolerance of trifoliate orange
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-11-01
    Fei Zhang, Ying-Ning Zou, Qiang-Sheng Wu, Kamil Kuča

    Arbuscular mycorrhizas enhance the drought tolerance of host plants through several underlying mechanisms. Polyamines (PAs) are known to protect plant cells from the damages of drought by enhancing the antioxidant defense system, restricting ethylene synthesis, maintaining cell pH and ion homeostasis, preventing chlorophyll loss, and so on; concomitantly, the mechanism through which arbuscular mycorrhizal (AM) fungi modulate PA metabolism to enhance drought tolerance of plants remains unclear. A pot experiment was conducted to assess how an AM fungus, Funneliformis mosseae, affects root PA homeostasis, activities and gene expression of PA-related synthesizing and degrading enzymes, hydrogen peroxide (H2O2, a PA metabolite) production, and antioxidant enzyme gene expression in trifoliate orange (Poncirus trifoliata) exposed to drought stress (DS). AM seedlings showed higher growth traits, leaf water potential, two plasma membrane intrinsic protein aquaporin gene expressions, and chlorophyll concentrations than non-AM seedlings under well-watered (WW) and DS conditions. Mycorrhizal treatment induced higher putrescine and cadaverine but lower spermidine and spermine concentrations, with higher activity of PA catabolic enzymes (copper-containing diamine oxidase, CuAO; polyamine oxidase, PAO) and putrescine synthases (ornithine decarboxylaseby; arginine decarboxylase, ADC). Mycorrhizas up-regulated the expression of the spermine synthase gene, PtSPMS, under DS, and down-regulated the transcript levels of PA catabolic enzyme genes (PtCuAO1, PtCuAO2, PtCuAO6, and PtCuAO8) and PA synthase genes (PtADC1 and PtADC2) under DS. PtPAO1, PtPAO2, and PtPAO3 had higher expression levels in AMF-inoculated seedlings, as compared to non-AMF-inoculated seedlings, under DS, triggering reactive oxygen species-related signalling for stress responsiveness through low H2O2 levels by up-regulating the expression of PtMn-SOD, PtCu/Zn-SOD, and PtCAT1. This study demonstrated that mycorrhizas have the capacity to modulate PA metabolism to enhance the drought tolerance of plants.

    更新日期:2019-11-01
  • RNA-Seq based transcriptomic analysis revealed genes associated with seed-flooding tolerance in wild soybean (Glycine soja Sieb. & Zucc.)
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2019-10-31
    Ripa Akter Sharmin, Mashiur Rahman Bhuiyan, Wenhuan Lv, Zheping Yu, Fangguo Chang, Jiejie Kong, Javaid Akhter Bhat, Tuanjie Zhao

    Seed-flooding stress is one of the most important constraints that affects the yield and quality of soybean. However, very little is known about the molecular mechanisms underlying seed-flooding tolerance. Hence, the present study investigated the transcriptome profile in root tissues of two contrasting soybean genotypes viz., PI342618B/SFT-tolerant, and NN86-4/SFS-sensitive under seed-flooding stress using RNA-Seq approach. A total of 1563 and 1958 differentially expressed genes (DEGs) were identified in SFT-tolerant and SFS-sensitive, respectively suggesting that the former is less affected by flooding stress. Both Gene ontology (GO) enrichment and MapMan pathway analyses revealed that response to seed-flooding stress was mostly enriched in the DEGs that are involved in the cell wall, antioxidant activity, catalytic and transcription factor activities as well as protein metabolism and signaling. Based on gene annotation, GO enrichment and protein-protein interaction (PPI) network analysis, a total of 807 DEGs were screened from the above terms related to the stress including response to stress, defense response and response to stimulus for candidate gene prediction analysis. Out of them, 51 genes revealing significant opposite gene expression pattern between tolerant and sensitive genotypes along with GmERFVII1, GmERFVII2 & GmERFVII3 and MAPK1 were predicted as the possible candidate genes for further analysis. Using quantitative real-time RT-PCR (qRT-PCR) and sequencing analysis, five of the randomly selected ten genes viz., Glyma.01G231200, Glyma.08G083300, Glyma.06G045400, Glyma.05G215900, and Glyma.15G015100 revealed both significant opposite expression pattern and nucleotide differences, respectively between SFT-tolerant and SFS-sensitive. Hence, these genes will be of great value for breeding seed-flooding tolerance in soybean after their proper functional validation. Overall, the transcriptome profiling indicates that all the three major processes viz., biological process (BP), cellular components (CC), and molecular functions (MF) are altered in the soybean in response to seed-flooding stress. In conclusion, these findings provide in-depth insights that will be of great utility for the exploration of candidate gene functions for seed-flooding tolerance in soybean.

    更新日期:2019-11-01
  • Design and performance of the Phyto-Nutri-Tron: a system for controlling the root and shoot environment for whole-plant ecophysiological studies.
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2001-09-07
    B Lorenzen,H Brix,H H Schierup,T V Madsen

    A controlled environment system, termed the Phyto-Nutri-Tron (PNT), has been established to study whole plant ecophysiological responses to multiple environmental factors. The PNT is a computer-controlled highly flexible growth facility with independent control of the shoot and the root environment. The facility consists of two growth cabinets each containing four separate hydroponic growth systems. The growth cabinets can be used as assimilation chambers with individual control of temperature, humidity, light, CO2 and monitoring of O2. The hydroponic growth systems are connected to nutrient supply units with disinfection systems and individual control of temperature, pH and oxygen. The ionic composition of the solutions has automated feedback control through a PO4 autoanalyzer and a flow injection analyzer which also analyzes NH4+, NO2- and NO3-. Other ions are automatically monitored by ICP-AES. The system has automated calibration procedures of the analytical equipment and prolonged studies of plant growth can be performed under constant environmental conditions. This paper describes the design and construction of the PNT, the results of a number of tests showing the degree of control of environmental factors and the results of a comparative study on NH4+ and NO3- uptake kinetics by Juncus effusus conducted in the PNT demonstrate the use of the PNT in ecophysiological studies.

    更新日期:2019-11-01
  • Differential growth resulting in the specification of different types of cellular architecture in root meristems.
    Environ. Exp. Bot. (IF 3.712) Pub Date : 1989-01-01
    Z Hejnowicz

    Symplastic growth of plant organs may be described by a continuous growth tensor field. In tensorial analysis of meristems, the trajectories of periclinal and anticlinal cell walls represent trajectories of the principal directions of growth (PDGs); this follows from the maintenance of mutual orthogonality between periclinal and anticlinal wall trajectories during growth. Periclinal and anticlinal cell divisions are also oriented in the principal planes of growth. The growth tensor for the root apex is specified in such a way that the principal directions of the tensor fit the pattern of periclinal and anticlinal walls in the apex, and that the grid formed by material particles aligned along PDG trajectories preserve this alignment during growth. Two growth tensors are formulated--one giving a maximum and the other giving a minimum of the volumetric relative elemental growth rate at the region of the initial cell(s). Temporal sequences of deformation of a grid formed by lines coinciding with the principal directions of growth are shown. The formation of cellular patterns in root apices is simulated. Two types of patterns are obtained: one with an apical cell and merophytes, and another with files of cells converging towards a quiescent centre.

    更新日期:2019-11-01
  • Differential growth and plant tropisms: a study assisted by computer simulation.
    Environ. Exp. Bot. (IF 3.712) Pub Date : 1989-01-01
    P W Barlow,P Brain,J S Adam

    Tropisms and other movements of a plant organ result from alterations in local rates of cell elongation and a consequent development of a growth differential between its opposite sides. Relative elemental rates of elongation (RELELs) are useful to characterize the pattern of growth along and round an organ. We assume that the value of the RELEL at a given point is dependent on distance from the tip and that the distribution of values along the organ surface can be characterized in terms of the spread and the position of the maximum value. A computer model is described which accommodates these parameters and simulates tropic curvatures due to differential growth. Additional regulatory functions help to return the simulated organ to its original orientation. Particular attention is given to the simulation of root gravitropism because here not only do each of the various growth and regulatory parameters have a known biological counterpart, but some can also be given an actual quantitative value. The growth characteristics relate to the biophysical properties of cells in the elongation zone of the root, while the regulatory functions relate to aspects of the graviperception and transmission systems. We believe that, given a suitably flexible model, computer simulation is a powerful means of characterizing, in a quantitative way, the contribution of each parameter to the elongation of plant organs in general and their tropisms in particular.

    更新日期:2019-11-01
  • The biophysics of differential growth.
    Environ. Exp. Bot. (IF 3.712) Pub Date : 1989-01-01
    A D Tomos,M Malone,J Pritchard

    The intrinsic control of uniform and differential growth of plant cells can be traced to a small number of physical parameters. These are cell wall rheology, membrane and tissue hydraulic conductivity, and membrane and tissue solute transport. Water and solute effects are manifested as alterations in turgor pressure. Environmental and biochemical processes always channel their effects through one or more of these parameters. Technical developments such as the pressure probe and Instron tensiometer, together with a reappraisal of older techniques, are beginning to allow assessment of the relative roles of these factors. Although the importance of cell wall rheology is becoming increasingly apparent, there is still insufficient information to allow generalized conclusions regarding the role of turgor pressure in differential growth. This review considers attempts to correlate these parameters with observed anatomical growth patterns.

    更新日期:2019-11-01
  • The genetic analysis of tropic responses.
    Environ. Exp. Bot. (IF 3.712) Pub Date : 1989-01-01
    C D Knight,D J Cove

    An increasing number of studies on tropic responses includes the genetic analysis of mutants defective in these morphogenetic processes. This review collates the information and discusses the implications of this approach to such studies. The review is organized on a systematic basis because most genetic analyses are insufficiently complete for general principles to have emerged. The most advanced analyses are those of lower eukaryotes because of their haploidy and the ease with which they can be manipulated in vitro. The extensive studies of phototropism, gravitropism and autochemotropism in the fungus Phycomyces blakesleeanus and of phototropism, polarotropism and gravitropism in the moss Physcomitrella patens are reviewed. In comparison with these studies, the genetic analysis of tropic responses in particular species of flowering plants is more limited. However, comparative physiological and ultra-structural studies of individual mutant and wild-type strains have been performed for a number of species. These results are discussed with particular regard to their support for established hypotheses.

    更新日期:2019-11-01
  • Plant movements caused by differential growth--unity or diversity of mechanisms?
    Environ. Exp. Bot. (IF 3.712) Pub Date : 1989-01-01
    R D Firn,A B Myers

    A very wide range of plant organ movements have been described and yet it is not clear how each of them is related to the others. This uncertainty has had two undesirable consequences. Firstly, some workers have accepted the idea of a vague unity in the area and have subsequently been misled by information obtained in one system and applied without adequate justification to a study of a quite different system. Secondly, some researchers have evoked a possible diversity to explain why a particular mechanistic explanation may continue to be valid even when the model fails to explain events of a very similar nature in a slightly different system. We argue that this confusion has resulted from a classification of organ movements which has been based on functional rather than on mechanistic considerations. Mechanistic unity is to be expected on evolutionary grounds. This unity, however, may apply only to certain elements of the stimulus-response chain, at certain levels of organization. It follows from this that in seeking this unity, comparisons should be made between equivalent elements of the stimulus-response chain at the same level of organization in different systems. Only when this is done will theories built around the concept of unity provoke meaningful discussion.

    更新日期:2019-11-01
  • Differential growth and hormone redistribution in gravireacting maize roots.
    Environ. Exp. Bot. (IF 3.712) Pub Date : 1989-01-01
    P E Pilet

    When growing roots are placed in a horizontal position gravity induces a positive curvature. It is classically considered to be the consequence of a faster elongation rate by the upper side compared to the lower side. A critical examination indicates that the gravireaction is caused by differential cell extension depending on several processes. Some of the endogenous regulators which may control the growth and gravitropism of elongating roots are briefly presented. The growth inhibitors produced or released from the root cap move preferentially in a basipetal direction and accumulate in the lower side of the elongation zone of horizontally maintained roots. The identity of these compounds is far from clear, but one of these inhibitors could be abscisic acid (ABA). However, indol-3y1 acetic acid (IAA) is also important for root growth and gravitropism. ABA may interact with IAA. Two other aspects of root cell extension have also to be carefully considered. An elongation gradient measured from the tip to the base of the root was found to be important for the growth of both vertical and horizontal gravireactive roots. It was changed significantly during the gravipresentation and can be considered as the origin of the differential elongation. Sephadex beads have been used as both growth markers and as monitors of surface pH changes when they contain some pH indicator. This technique has shown that the distribution of cell extension along the main root axis is related to a pH gradient, the proton efflux being larger for faster growing parts of roots. A lateral movement of calcium is obtained when Ca2+ is applied across the tips of horizontally placed roots with a preferential transport towards the lower side. Endogenous calcium, which may accumulate inside the endoplasmic reticulum of some cap cells, may also act in the gravireception. These observations and several others strongly suggest that calcium may play an essential role in controlling root growth and several steps of the root gravireaction.

    更新日期:2019-11-01
  • Phototropism involves a lateral gradient of growth inhibitors, not of auxin. A review.
    Environ. Exp. Bot. (IF 3.712) Pub Date : 1989-01-01
    J Bruinsma,K Hasegawa

    During phototropic curvature, indolyl-3-acetic acid (IAA) remains evenly distributed in the hypocotyl of sunflower (Helianthus annuus L.) and in the oat (Avena sativa L.) coleoptile. At the irradiated side, growth inhibiting substances accumulate. In sunflower, basipetal movement of a growth factor is not involved, since the top of the seedling can be covered or removed without affecting the photo-tropic response; this response, moreover, is independent of the rate of elongation growth. The chemical nature of the growth-inhibiting substances is only partly known. In the hypocotyl they occur in the neutral fraction: in sunflower cis-xanthoxin is one of them, in radish (Raphanus sativus L.) cis- and trans-raphanusanins, and possibly raphanusamide, are involved. The inhibitor(s) in the oat coleoptile are acidic. During curvature, their amount remains rather constant but the distribution changes with an accumulation at the irradiated side. It is concluded that phototropic curvature is brought about by an accumulation, at the irradiated side, of growth-inhibiting substances that unilaterally reduce cell elongation even though the IAA distribution is uniform.

    更新日期:2019-11-01
  • Differential growth in plants--a phenomenon that occurs at all levels of organization.
    Environ. Exp. Bot. (IF 3.712) Pub Date : 1989-01-01
    P W Barlow

    Differential growth is a feature of cells, the organs which they construct and the whole plant itself. The control of differential growth at each of these three levels of organization resides in the level lower than that in which it is expressed. Thus, differential growth of cells is regulated by the patterns of intracellular microtubules and cellulose microfibrils of the walls, that of organs by the pattern of growth of their cells, and that of the organism by the relative rates of organ growth. The latter is, in turn, determined an all-pervading system of correlative interactions. Plant hormones by may play a role in each of these regulatory systems.

    更新日期:2019-11-01
  • Growth, proline accumulation and water relations of NaCl-selected and non-selected callus lines of Dactylis glomerata L.
    Environ. Exp. Bot. (IF 3.712) Pub Date : 1995-01-01
    S Dutta Gupta,R M Augé,P D Denchev,B V Conger

    Sodium chloride-tolerant calli were selected from leaf-derived embryogenic calli of Dactylis glomerata L. on agar solidified medium supplemented with 200 mM NaCl, a concentration lethal to non-selected calli. Growth characteristics, water relations and proline accumulation pattern were compared in selected and non-selected lines. The objective was to gain an understanding of the mechanism(s) of tolerance in the NaCl-tolerant line. Growth in the selected line, as expressed in terms of tolerance index (ratio of fresh wt. on NaCl medium:fresh wt. on NaCl free medium x 100), was greater than that of the non-selected line at all levels of NaCl between 50 and 300 mM. There was no significant difference in proline accumulation in the selected and non-selected lines. Maintenance of turgor by osmotic adjustment was observed in the non-selected line despite decreased growth. In contrast, the selected line lost either the need or the ability to adjust osmotically. There was little or no increase in symplastic osmolality in the selected line when exposed to NaCl. Presumably, selection was made for a salt-excluding tissue that has lost the ability to accumulate solutes and adjust turgor with NaCl stress.

    更新日期:2019-11-01
  • Influence of elevated CO(2) on the sensitivity of two soybean cultivars to sulphur dioxide.
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2001-05-30
    S S. Deepak,M Agrawal

    Two cultivars of soybean (Glycine max cv. Bragg and PK 472) were subjected to elevated concentrations of CO(2) (600 &mgr;l l(-1)) and/or SO(2) (0.06 &mgr;l l(-1)), for 8 h from germination to grain maturity in open top chambers under field conditions to assess the modification in response to SO(2) exposure resulting form CO(2) enrichment. Exposure to SO(2) alone resulted in reductions in plant growth, biomass and yield, as well as declines in foliar starch and protein content in both the cultivars of soybean. Elevated CO(2) stimulated plant growth, yield and enhanced foliar starch content, photosynthesis and WUE in both the cultivars. In plants exposed to the combination of elevated CO(2)+SO(2), the adverse influence of SO(2) was mitigated by CO(2) enrichment. This effect was considered to result from the provision of extra carbon sources required for repair and detoxification processes and a reduction in SO(2) uptake through reduction in stomatal conductance. PK 472 exhibited greater sensitivity to SO(2) than Bragg. PK 472 also showed greater stimulation of yield under CO(2)+SO(2) treatment than Bragg.

    更新日期:2019-11-01
  • Aluminum-induced cell death in root-tip cells of barley.
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2001-05-30
    J -w. Pan,M -y. Zhu,H Chen

    Aluminum-induced cell death was investigated in root-tip cells of barley (Hordeum vulgare). The growth of roots in 0.1-50 mM Al treatments was inhibited after 8 h treatments, and could not be recovered after 24 h recovery culture without Al. Viable detection with fluorescein diacetate-propidium iodide (FDA-PI) staining shows that most of the root-tip cells have lost viability. These results suggest that the irreversible inhibition of root growth after 8 h Al treatments or 24 h recovery culture is mainly caused by cell death. DNA ladders occurred in root tips only after 8 h Al treatments (0.1-1.0 mM), but no apoptotic bodies in root tips were observed. Thus, the cell death caused by Al stress is likely to be Al-induced programmed cell death (PCD). The reactive oxygen species (ROS) in root-tip cells measured by ultraweak luminescence indicated that the oxidation status in root-tip cells basically ceased after exposure to 10-50 mM Al for 24 h, but was very violent in the root-tip cells treated with 0.1-1.0 mM for 24 h. Exposure to 0.1-1.0 mM Al for 3-12 h led to ROS burst. Therefore, our results suggest that 0.1-1.0 mM Al treatments for 8 h induce cell death (Al-induced PCD) possibly via a ROS-activated signal transduction pathway, whereas 10-50 mM Al treatments may cause necrosis in the root-tip cells. These results have an important role for further studies on the mechanism of Al toxicity in plants.

    更新日期:2019-11-01
  • Root dynamics in an artificially constructed regenerating longleaf pine ecosystem are affected by atmospheric CO(2) enrichment.
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2001-05-30
    S G. Pritchard,M A. Davis,R J. Mitchell,S A. Prior,D L. Boykin,H H. Rogers,G B. Runion

    Differential responses to elevated atmospheric CO(2) concentration exhibited by different plant functional types may alter competition for above- and belowground resources in a higher CO(2) world. Because C allocation to roots is often favored over C allocation to shoots in plants grown with CO(2) enrichment, belowground function of forest ecosystems may change significantly. We established an outdoor facility to examine the effects of elevated CO(2) on root dynamics in artificially constructed communities of five early successional forest species: (1) a C(3) evergreen conifer (longleaf pine, Pinus palustris Mill.); (2) a C(4) monocotyledonous bunch grass (wiregrass, Aristida stricta Michx.); (3) a C(3) broadleaf tree (sand post oak, Quercus margaretta); (4) a C(3) perennial herbaceous legume (rattlebox, Crotalaria rotundifolia Walt. ex Gemel); and (5) an herbaceous C(3) dicotyledonous perennial (butterfly weed, Asclepias tuberosa L.). These species are common associates in early successional longleaf pine savannahs throughout the southeastern USA and represent species that differ in life-form, growth habit, physiology, and symbiotic relationships. A combination of minirhizotrons and soil coring was used to examine temporal and spatial rooting dynamics from October 1998 to October 1999. CO(2)-enriched plots exhibited 35% higher standing root crop length, 37% greater root length production per day, and 47% greater root length mortality per day. These variables, however, were enhanced by CO(2) enrichment only at the 10-30 cm depth. Relative root turnover (flux/standing crop) was unchanged by elevated CO(2). Sixteen months after planting, root biomass of pine was 62% higher in elevated compared to ambient CO(2) plots. Conversely, the combined biomass of rattlebox, wiregrass, and butterfly weed was 28% greater in ambient compared to high CO(2) plots. There was no difference in root biomass of oaks after 16 months of exposure to elevated CO(2). Using root and shoot biomass as a metric, longleaf pine realized the greatest and most consistent benefit from exposure to elevated CO(2). This finding suggests that the ability of longleaf pine to compete with sand post oak, a common deciduous tree competitor, and wiregrass, the dominant understory herbaceous species, in regenerating ecosystems may be significantly enhanced by rising atmospheric CO(2) concentrations.

    更新日期:2019-11-01
  • Compressive/tensile stresses and lignified cells as resistance components in joints between cladodes of Opuntia laevis (Cactaceae): responses to applied stresses.
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2001-05-30
    L S. Evans,Z Kahn-Jetter,C Frenz,J Pancrudo,K Lagrazon

    Cactaceae are a diverse group of plants with a wide variety of morphologies and reproductive strategies. Many species have segmented stems in which terminal cladodes may be separated from main stem cladodes with varying amounts of resistance. Previous results demonstrated that lignified xylem cells in tensile portions of stem joints provide the main resistance to separation of cladodes within cactus plants. The purpose of the present study was to determine if stem joints of Opuntia laevis would produce additional lignified xylem cells in response to additional externally applied stresses. Normal average stress levels, which accompany the addition of a new cladode, were applied to 12 plants. In contrast, double the average stress levels were applied to 13 other plants. After exposure to the two stress regimens for 6 months, the amount and location of lignified xylem cells in joint segments were similar for both stress treatments. So, although the results support the hypothesis that lignified xylem cells act as the main resistance to stress at joints of cladodes, doubling the normal amount of applied stress was insufficient to alter the amount or location of lignified xylem cells in stem joints. These results indicate that normal amounts of lignified xylem cells can resist up to two times the normal amount of stress for 6 months without producing additional lignified xylem cells.

    更新日期:2019-11-01
  • Nitrate reductase activity, distribution, and response to nitrate in two contrasting Phaseolus species inoculated with Rhizobium spp.
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2001-05-30
    J A.G. Silveira,J C.S. Matos,V M. Cecatto,R A. Viegas,J T.A. Oliveira

    The nitrate reductase activity distribution and response of two nodulated species of Phaseolus (Phaseolus vulgaris-common bean, and Phaseolus lunatus-lima bean) to different exogenous nitrate levels were studied during the vegetative period. These Phaseolus species showed to be very contrasting in respect to the pattern of nitrate reductase (NR) activity distribution thought the plant. The highest level of NR activity in P. vulgaris was clearly shown to occur in leaves in contrast with the lowest one detected in roots and nodules as widely seen for other tropical species of the Phaseoleae tribe. Conversely, P. lunatus had higher NR activity in the nodules, whereas its leaves exhibited a steadily decrease during the plant development. Indeed, at 32 days after emergence (pre-flowering stage), the nodulated P. vulgaris had approximately 95% of the total NR activity localized in its leaves, whereas in P. lunatus it was equally distributed in the nodules and in the leaves. Under long-term exposure to increasing exogenous level of nitrate, the leaf-NR activity of nodulated P. vulgaris presented a positive response, whereas the enzyme activity was very low and unresponsive in P. lunatus. In contrast, the nodule-NR activity showed a reverse response to the increasing NO(3)(-) level. The nodule-NR activity of P. lunatus significantly increased whereas in the P. vulgaris nodules it was very low and unresponsive. This present study suggests that P. lunatus inoculated with Rhizobium tropici presents a singular pattern of nitrate reduction distribution among leaves and nodules during the vegetative development. It is speculated that the nodulated Phaseolus lunatus may have different NR isoforms in their leaves (at least a constitutive type) and an inducible form in their nodules, responsive to long-term exposure to nitrate.

    更新日期:2019-11-01
  • Atmospheric H(2)S as sulfur source for Brassica oleracea: kinetics of H(2)S uptake and activity of O-acetylserine (thiol)lyase as affected by sulfur nutrition.
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2001-05-30
    C E.E. Stuiver,L J. De Kok

    The uptake of hydrogen sulfide (H(2)S) by shoots of curly kale (Brassica oleracea) showed saturation kinetics with respect to the atmospheric concentration. The kinetics are largely determined by the rate of metabolism of the absorbed H(2)S into cysteine, catalyzed by O-acetylserine (thiol)lyase, and can be described by the Michaelis-Menten equation. When B. oleracea was grown under sulfate (SO(4)(2-))-deprived conditions, plants developed sulfur (S) deficiency symptoms and H(2)S uptake kinetics were substantially altered. Shoots of SO(4)(2-)-deprived plants had a lower affinity to H(2)S uptake, whereas the maximal H(2)S uptake rate was higher. When SO(4)(2-)-deprived plants were simultaneously exposed to 0.2 &mgr;l l(-1) H(2)S all S deficiency symptoms disappeared and H(2)S uptake kinetics returned rapidly to values observed for S-sufficient shoots. The activity of the H(2)S-fixating enzyme O-acetylserine (thiol)lyase was hardly affected upon either prolonged H(2)S exposure or SO(4)(2-) deprivation. Evidently, the activity of O-acetylserine (thiol)lyase was not the rate-limiting step in the H(2)S uptake by shoots. The significance of the in situ availability and rate of synthesis of the substrate O-acetylserine for O-acetylserine (thiol)lyase as determining factor in the uptake kinetics of H(2)S needs further evaluation.

    更新日期:2019-11-01
  • Glycine betaine involvement in freezing tolerance and water stress in Arabidopsis thaliana.
    Environ. Exp. Bot. (IF 3.712) Pub Date : 2001-05-30
    W Xing,C B. Rajashekar

    Levels of endogenous glycine betaine in the leaves were measured in response to cold acclimation, water stress and exogenous ABA application in Arabidopsis thaliana. The endogenous glycine betaine level in the leaves increased sharply during cold acclimation treatment as plants gained freezing tolerance. When glycine betaine (10 mM) was applied exogenously to the plants as a foliar spray, the freezing tolerance increased from -3.1 to -4.5 degrees C. In addition, when ABA (1 mM) was applied exogenously, the endogenous glycine betaine level and the freezing tolerance in the leaves increased. However, the increase in the leaf glycine betaine level induced by ABA was only about half of that by the cold acclimation treatment. Furthermore, when plants were subjected to water stress (leaf water potential of approximately -1.6 MPa), the endogenous leaf glycine betaine level increased by about 18-fold over that in the control plants. Water stress lead to significant increase in the freezing tolerance, which was slightly less than that induced by the cold acclimation treatment. The results suggest that glycine betaine is involved in the induction of freezing tolerance in response to cold acclimation, ABA, and water stress in Arabidopsis plants.

    更新日期:2019-11-01
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