Abstract Coronatine (COR) is a phytotoxin produced by Pseudomonas syringae and is a functional analogue of the bioactive hormone JA-Ile, which is widely involved in plant defence responses. In this study, we explored the effects of exogenous applications of COR on tobacco plants under polyethylene glycol-induced drought stress. Compared with control (CK), COR-treated tobacco plants exhibited higher leaf relative water content and better photosynthetic performance under drought exposure. Ultrastructural examination revealed that drought led to stomatal closure and disorganization of granum stacking in the chloroplasts (with obvious accumulation of plastoglobuli), and mitochondria in the CK samples presented injured cristae. In the leaf tissue of the COR-treated plants, regularly stacked granum thylakoids, few plastoglobuli and intact mitochondrial membranes and cristae were observed. Totals of 1803 and 6207 differentially expressed genes (DEGs) were identified between the samples from the COR-treated and CK plants under well-watered and drought conditions. Functional annotation analysis revealed that these DEGs were involved mainly in plant hormone signal transduction, cellular carbohydrate metabolic processes and photosynthesis processes. Six hundred forty transcription factor genes were also identified among the DEGs. This study provides a global view of COR-induced drought stress tolerance in tobacco from both physiological and transcriptional aspects.

Abstract Detoxification of reactive carbonyl compounds (RCC) is crucial to sustain cellular activity to improve plant growth and development. Seedling growth is highly affected by accumulation of RCC under stress. We report non-enzymatic, enzymatic mechanisms of detoxification of RCC in the cucumber, tobacco and rice seedling systems exposed to glucose, NaCl, methyl viologen (MV) induced oxidative stress. The cucumber seedlings exposed to carbonyl stress had higher levels of malondialdehyde (MDA), protein carbonyls (PCs) and advanced glycation end-product N-carboxymethyl-lysine (AGE-CML) that negatively affected the seedling growth. The overexpression of enzyme encoding aldo-keto reductase-1 (AKR1) in tobacco and rice showed detoxification of RCC, MDA and methylglyoxal (MG) with improved seedling growth under glucose, NaCl and MV-induced oxidative stress. Further, small molecules like acetylsalicylic acid (ASA), aminoguanidine (AG), carnosine (Car), curcumin (Cur) and pyridoxamine (PM) showed detoxification of RCC non-enzymatically and rescued the cucumber seedling growth from glucose, NaCl and MV-stress. In autotrophically grown rice seedlings these molecules substantially improved seedling growth under MV-induced oxidative stress. Seedlings treated with the small molecules sustained higher guaiacol peroxidase (GPX) enzyme activity signifying the role of small molecules in reducing carbonyl stress-induced protein inactivation and AGE-CML protein modifications. The results showed that besides enzymatic detoxification of RCC, the small molecules also could reduce cytotoxic effect of RCC under stress. The study demonstrates that small molecules are attractive compounds to improve the seedling growth under stress conditions.

Abstract The promoting effects of both high nitrogen (N) and exogenous gibberellin (GA) supply on regrowth of Lolium perenne have been widely reported. The mobilisation of carbohydrate reserves in response to N is a critical mechanism for promoting plant regrowth. However, our knowledge about GA regulation of carbohydrate metabolism remains limited. Here, we analysed the effects of both N and exogenous GA on the molecular mechanisms controlling perennial ryegrass regrowth and investigated the similarities and differences. Our analyses show that both high N and exogenous GA supply lead to a decline in the accumulation of carbohydrate reserves, but the regulatory mechanisms responsible for this decline varied between N and GA supply. The effects of elevated N were mainly through declining fructan biosynthesis which results in improving photosynthate use efficiency to promote plant regrowth, whereas the application of exogenous GA resulted in an increase in the hydrolytic activities of fructan exohydrolase and invertases capable of cleaving reserved carbohydrates to release energy sources for plant regrowth.

Abstract The current investigation aimed to evaluate the role of silicon forms on sweet basil (Ocimum basilicum L.) biomass and essential oil (EO) production, as well as some physiological and ultrastructural modification under different irrigation regimes. Drought significantly decreased plant growth, photosynthetic pigment, ion, relative water content, catalase activity, and EO yield, meanwhile, increased organic and antioxidant solute concentration, EO percentage, peroxidase activity, and oxidative impairment criteria (hydrogen peroxide, lipid peroxidation, and membrane permeability percentage). Concerning EO constituents, linalool and methyl chavicol were the major components that decreased under drought relative to well-watered plants. Exogenous application of silicon forms under well-watered or drought condition may fully or partially compensate to some extent to sweet basil plant development and biochemical attributes (photosynthetic pigment, ion percentage, antioxidant solutes, and organic osmolytes). The maximum EO yield was obtained by 250 mg L−1 sodium metasilicate (Si) under mild drought. Cell organelles exhibited a different degree of malformation and lyse under severe drought; conversely, application of Si forms nullify the abovementioned injuries caused by drought. In conclusion, application of 250 mg L−1 Si improved drought tolerance in sweet basil herb and EO yield by accelerating their antioxidant system, osmoregulation, and maintaining organelles ultrastructure that induced herb growth and EO yield.

Abstract Bacterial species in the plant-beneficial-environmental branch of Alcaligenes characterize an important part of rhizosphere microbes. The effects of plant growth-promoting Alcaligenes sp. AZ9 (accession #KU494828) on soil status and maize (Zea mays L.) performance were evaluated in single or combined applications with soil amendments, such as biochar (BC) prepared through pyrolysis of maize straw at 300 ºC, rock phosphate enriched compost (CM), and humic acid (HA) in two wirehouse experiments under natural environment. Qualitative P solubilization of Alcaligenes sp. AZ9 revealed the appearance of a halo zone up to 19.1 mm in agar medium with P solubilizing index 4.27 and P solubilizing efficiency 327%. Alcaligenes sp. AZ9 showed solubilization of P up to 30.85 µg mL−1 by lowering pH of medium from 7.0 to 5.25. The application of Alcaligenes sp. AZ9 significantly improved soil biological attributes, such as bacterial colony forming unit by 20.5%, soil organic carbon by 10.3%, soil organic matter by 5.1%, and water content of saturated soil by 5.7%. The combined application of Alcaligenes sp. AZ9 with either BC, CM, or HA or with their mixture (BC plus CM plus HA) significantly increased the above biological attributes of soil than the application of Alcaligenes sp. AZ9 alone. Moreover, the integrated application of Alcaligenes sp. AZ9 with BC, CM, and HA significantly improved growth and yield attributes of maize in terms of root length (26%), plant height (39%), shoot fresh biomass (31%), shoot dry biomass (32%), root fresh biomass (30%), root dry biomass (34%), 100-grains weight (26%), stover yield (28%), and grain yield (19%). Similarly, the integrated application of Alcaligenes sp. AZ9 with BC, CM, and HA promoted N, P, and K in maize grain concentration by 12%, 11%, and 11%, respectively, compared with the application of organic amendments without Alcaligenes sp. AZ9. Combined application of Alcaligenes sp. AZ9 with BC, CM, and HA could be an effective strategy to improve plant growth, nutrients uptake, and yield of maize in the context of sustainable agriculture. In future research, the effects of integrated application of Alcaligenes sp. AZ9 with BC, CM, and/or HA should be further evaluated under field conditions.

Abstract A pot study was performed to examine the effect of plant growth-promoting rhizobacteria (PGPR) including Azospirillum lipoferum or Azotobacter chroococcum on growth criteria (leaf area and seedlings fresh and dry weight), pigments [chlorophylls (Chl a and b) and carotenoids], osmolytes (soluble sugars, soluble proteins and proline), nutrient uptake, antioxidant enzyme activities, and oxidative stress in maize plants under normal and salt-affected soils. The results showed that salt stress induced a reduction in growth traits, pigments, soluble proteins, K+, and K+/Na+ ratio. On the other side, it increased soluble sugars, proline, Na+, malondialdehyde (MDA), and the activity of peroxidase (POD) and catalase (CAT). Meanwhile, salt stress did not significantly change the activity of ascorbate peroxidase (APX) in maize plants. The inoculation using Azospirillum lipoferum or Azotobacter chroococcum significantly enhanced growth parameters, pigments, K+, osmolytes, K+/Na+ ratio, and the activity of CAT, POD, and APX of the salt-affected maize plants as well as uninoculated control plants. In addition, the results showed that both types of bacteria have attributed to lower MDA and Na+ in maize plants. Interestingly, Azospirillum lipoferum has affected more compared to Azotobacter chroococcum in control and salt-stressed plants. We, therefore, have observed in this study that microbial inoculation significantly improved plant physiological activities and that adding bacteria such as Azospiroillum or Azotobacter to the soil could mitigate the negative effects of salt stress on maize plants.

Abstract Plant growth is affected by a plethora of environmental factors including microorganisms. Trichoderma species are free-living fungi which are beneficial to plant by stimulating growth and disease resistance of plant, not only in the rhizosphere but also in the aerial parts. Here, we investigated the role of MAPK-mediated activation of plasma membrane (PM) H+-ATPase in regulating the leaf colonization of Trichoderma viride Tv-1511 and its growth-promoting effects in Arabidopsis. T. viride Tv-1511 colonized in the leaves of wild-type Arabidopsis leaves and induced the growth-enhanced phenotypes including increased biomass production, elevated nutrient uptake and stimulated leaf and seedling development. PM H+-ATPase plays an important role in the plant development and environmental responses. Results showed that PM H+-ATPase activity and expression of AHA1 gene was enhanced in T. viride Tv-1511-inoculated Arabidopsis. AHA1-deficiency inhibited the colonization of T. viride Tv-1511 in Arabidopsis leaves, and mutants in AHA1 gene were found to reduce the growth-promoting and developmental effects of T. viride Tv-1511 inoculation. Furthermore, MAP kinase 6 (MPK6) was determined to be activated by T. viride Tv-1511 inoculation, and involved in the leaf colonization and growth promotion induced by T. viride Tv-1511 by regulating the elevated expression and activity of PM H+-ATPase in Arabidopsis inoculated by T. viride Tv-1511. Taken all, our results highlighted the important role of MPK6-mediated increase of PM H+-ATPase expression and activity in the regulation of leaf colonization and plant growth promotion of T. viride Tv-1511.

Abstract Male germline specification is a crucial step in double fertilization in flowering plants. Determining which genes are activated in the male germline, and how those genes are regulated, is essential to understand double fertilization. However, transcription activities in the male germline may be not easy to detect due to low-level expression of some genes and technical difficulties of isolating male germline cells. Here, through a series of gene reporter assays in Arabidopsis, we showed a weak male germline expression pattern of the SOLO DANCERS (SDS) gene, which was confirmed by RT-PCR. Compared to directly fusing the SDS sequence with GFP, adding the coding sequences of other genes such as CDKA1 can greatly enhance the detection of the male germline expression pattern of SDS. We found that SDS expression in the male germline is activated by a novel pathway that differs from the well-known DUO1 regulon. We also developed an SDS-based fluorescence reporter to analyze posttranscriptional regulation in the male germline. Our data suggest that stable gene products of CDKA1 and others may enhance the sensitivity of gene reporters, and the male germline may use diverse pathways to activate gene expression.

Salt stress represents the most unfortunate abiotic stress factor in agricultural areas worldwide and contributes a severe reduction in growth, development, and yield of crop plants. Kenaf is a salt-tolerant crop. However, molecular mechanisms of salt stress tolerance in kenaf are not well elucidated. In the present study, seed germination parameters and cytological and transcriptome responses of leaves from two cultivars of kenaf (salt-tolerant P3A and salt-sensitive P3B) were analyzed between 250 and 0 mM NaCl treatments. Results indicated that under salt stress cultivar P3A had higher seed germination energy, germination index, and germination percentage with the less relative rate of salt damage than cultivar P3B. Furthermore, cytological studies indicated swelling and vacuolization of chloroplast and thylakoid in cultivar P3A under the influence of salt stress; however, chloroplast and thylakoid were degraded in cultivar P3B. Transcriptome analysis generated 8466 and 9333 differentially expressed unigenes (DEGs) (FDR ≤ 0.05 and log2FC ≥ 1) between salt-stressed and control treatments in cultivar P3A and cultivar P3B, respectively. Eight DEGs were selected randomly for quantitative real-time PCR to test the reliability of transcriptome sequencing results. Several genes encoding transcription factors WRKY, AP2/EREBP, and Hsfs families and genes like LEA, PsbA, PK, GSTs, NPR1, and TGA were induced under salt stress, and expression levels were higher in the cultivar P3A compared to cultivar P3B. The GO enrichment and KEGG pathway analysis suggested that these DEGs were related to ionic homeostasis and transport, osmotic adjustment, water deficit response, antioxidants, ROS scavenging, cellular membranes protection, photo-damage repairing cycle of photosystem II, thylakoid part, plant hormone signal transduction pathway, and may be related to salt tolerance in kenaf.

Melatonin is a natural phytohormone that occurs in most plants. It can regulate not only plant growth and development but also alleviate biotic and abiotic stress in plants. However, no studies have reported on endogenous melatonin increasing tomato tolerance to salt stress. In the present study, we observed that the overexpression of caffeic acid O-methyltransferase 1 (SlCOMT1) increased melatonin levels in tomato plants. We also observed that transgenic plants exhibited higher salt stress tolerance. SlCOMT1 overexpression could maintain the balance of Na+/K+ and decrease ion damage by activating salt overly sensitive (SOS) pathway under salt treatment. In addition, SlCOMT1 overexpression significantly enhanced the antioxidant capability, with higher antioxidant enzyme activity observed, including superoxide dismutase, peroxide and catalase activity, and higher ascorbic acid (AsA) and glutamate (GSH) accumulation levels. SlCOMT1 overexpression also maintained good nutrient homeostasis in the tomato plants. In addition, SlCOMT1 overexpression upregulated some stress-related genes (AREB1, AIM1, MAPK1, WRKY33 and CDPK1), which resulted in the activation of downstream signaling pathways and could be partly responsible for the improvement in salt stress tolerance.

Chickpea (Cicer arietinum L.) is an important grain crop mainly grown in arid and semi-arid regions of the world. Drought is the major factor limiting chickpea growth and productivity. Transcription factors (TFs) genes have been reported as key regulators of drought tolerance in plants. In this study, we determined the relative gene expression of transcription factors of WRKY, DREB2A, and CarNAC3 in three weeks seedlings of tolerant (MCC537) and susceptible (MCC674) genotypes under progressive water deficit through semi-quantitative reverse transcriptase PCR (SqRT-PCR) method. Furthermore, results of SqRT-PCR were more confirmed by quantitative PCR (qPCR). Relative gene expression analysis of the selected genes using qPCR revealed different dehydration-responsive expression patterns. The expression of WRKY gene was significantly induced in both tolerant and sensitive genotypes under severe drought stress (at the last time point). Also, in tolerant genotype, DREB2A gene was approximately expressed three, five and fourfold higher than control plants at three times points, respectively. Moreover, the expression level of CarNAC3 gene in this genotype increased four and twofold higher compared to the relative control at 2 and 4 days after stress, respectively. However, the expression of these genes in the susceptible genotype was constant or decreased relative to the control. Furthermore, the CarNAC3 and DREB2A genes showed higher and more effective expression than the WRKY gene. Overall, the results demonstrated that these TFs may play an important role to improve drought tolerance and have a potential to facilitate molecular breeding and development of drought-tolerant chickpea varieties.

Soil salinity severely affects cultivation in arid and semi-arid regions. It causes, among other things, an imbalance in the mineral nutrition of plants which results in yields’ decrease. One of the research’s approaches to mitigate the effects of these constraints is to look at the interaction between sodium chloride and phosphorus. The aim is to study the action of phosphorus to reduce the harmful effects of salinity. This study was undertaken in a greenhouse, in a pot of vegetation. The model plant used is Sorghum (Sorghum vulgar var rocket). The interaction NaCl (S) × P is carried out with four concentrations of NaCl (S0 = 0.1 dS m−1, S1 = 2 dS m−1, S2 = 8 dS m−1, S3 = 32 dS m−1) and four doses of TSP (PO = 0 mg/pot, P1 = 200 mg/pot, P2 = 400 mg/pot, P3 = 819 mg/pot), that is 16 (SP) processing. The results obtained made it possible to identify the effect of the SP processing on the morphological parameters, on the assimilation of the NPK's major elements, and on the accumulation of proline. They clearly showed that by adding phosphorus there was a remarkable improvement as the Sorghum displayed tolerance towards salinity. This improvement is manifested by an increase in stem height, dry material yield, nitrogen and phosphorus uptake, and proline accumulation. The results obtained suggest that Sorghum culture in saline medium (EC ≤ 32 dS m−1) is possible.

The effects of an exogenous organic carbon source (i.e., glucose) and indole-3-acetic acid (IAA) on root architecture and carbon–nitrogen (C–N) metabolism of apple rootstock were evaluated under soil organic matter (SOM)-restricted conditions. Malus baccata (L.) Borkh. seedlings were exposed to 1.5 g kg−1 glucose (GLC), 0.09 g kg−1 IAA, 0.06 g kg−1 2,3,5-triiodobenzoic acid (TIBA, a widely used auxin polar transport inhibitor), GLC + IAA, or GLC + TIBA for 30 days. Both GLC and IAA promoted root architecture and growth by regulating SHY2, SHR, ALF4, and LBD11. They also enhanced C–N metabolism, and accelerated nitrate transformation to amino acids. In contrast, TIBA reduced endogenous IAA content in root and inhibited plant growth and C–N metabolism by downregulating expression of auxin polar transport genes, although auxin biosynthesis genes were induced. These adverse effects could be alleviated in GLC + TIBA, which exhibited higher endogenous IAA content in root than TIBA-treated seedlings alone, due to the upregulated expression of auxin biosynthesis genes (YUCCA8, TAR2, TAA1, and CYP79B3) and polar transport genes (PIN1, AUX1, and LAX2). In addition, the enhanced transcription and activities of enzymes involved in C metabolism (PEPC, NADP-ME, and NADP-ICDH) could provide more organic acids, adenosine triphosphate (ATP), and energy charge for N metabolism in roots under GLC + TIBA than in roots under TIBA. The induced NR, GS, NADH-GDH, NADH-GOGAT activities and mRNA levels of genes involved in N metabolism indicated the higher N assimilation ability in roots under GLC + TIBA than in roots under TIBA alone. In conclusion, exogenous glucose-mediated IAA biosynthesis and polar transport regulates root architecture and C–N metabolism of M. baccata (L.) Borkh. under low-SOM conditions.

The original version of this article unfortunately contained an error in Funding section. The authors would like to correct the error with this erratum.

Our understanding of the developmental changes that occur during top leader elongation in gymnosperms lags behind that in angiosperms. We developed a semiquantitative method for determining epidermal cell size, by measuring the Feret diameter after cell wall staining of stem epidermal peels. This method allowed a large number of cells to be measured at various locations in the top leader of the Christmas tree Abies nordmanniana. Further, we have identified the growth rate of individual sections of the top leader, and the relationship between cell length and needle arrangement throughout the top leader. At bud break, all stem units begin to elongate simultaneously, but growth ceases from the base upwards during top leader elongation. Long top leaders were characterized by having up to three times as long cells at the base compared to short top leaders, whereas the cell lengths were similar in the apical region independent of the given plant growth capacity. In the basal sector, the level of auxin was much higher, whereas the levels of cytokinins were lower than in the apical sector, causing the auxin/cytokinin ratio to change from about 3 in the apical sector to more than 20 in the basal part. The Fibonacci number changed in the apical sector due to an increased cell number in the stem units and therefore longer distance between the needles. We conclude that the general growth pattern during top leader elongation in A. nordmanniana is similar to angiosperms but differs at the cellular level.

Industrialization and inevitable mining have resulted in the release of some metals in environment, which have different uses on the one hand and also showed environmental toxicity. Lithium (Li) is one of them; however, its excess use in different fields or inappropriate disposal methods resulted in high Li accumulation in soil and groundwater. This subsequently is affecting our environment and more potentially our arable crop production system. In humans, Li has been extensively studied and causes numerous detrimental effects at different organ levels. Moreover, increases in Li in groundwater and food items, cases for mental disorders have been reported in different regions of the world. In plants, only a few studies have been reported about toxic effects of lithium in plants. Moreover, plant products (fruits, grains or other plant parts) could be a major source of Li toxicity in our food chain. Therefore, it is more imperative to understand how plants can be developed more tolerant to Li toxicity. In this short mini-review article, we primarily highlighted and speculated Li uptake, translocation and Li storage mechanism in plants. This article provides considerable information for breeders or environmentalist in identifying and developing Li hyperaccumulators plants and environment management.

Expansin (EXP) plays an important role in plant root formation. The EXP genes associated with chrysanthemum roots have not yet been reported. Here we isolated a root-specific EXP gene in chrysanthemum (Chrysanthemum morifolium), namely CmEXPA4. Bioinformatics analysis showed that CmEXPA4-encoded protein has a conserved DPPB (Double-Psi Beta-Barrel) domain in the N-terminal with a series of Cys residues, an HFD (His-Phe-Asp) motif in the central region, and a pollen allergen domain in the C-terminal. The protein also has a specific α-insertion of WCNP (Trp-Cys-Asn-Pro), which suggests that it belongs to the A-subgroup of the EXP family. In the present study, we cloned the 1,129 bp promoter region upstream of CmEXPA4, and the analysis revealed an abundance of cis-acting elements associated with hormones, light and stress-related responses, and some root-specific regulatory elements in particular. Subcellular localization results indicated that CmEXPA4 locates in the cell wall. Exogenous indole butyric acid induced the up-regulation of CmEXPA4 expression, whereas exogenous abscisic acid inhibited its expression. Tissue expression analysis showed that CmEXPA4 was preferentially expressed in the roots and was synchronized with the rapid emergence of the root. These results suggested that CmEXPA4 may act on the growth and development of chrysanthemum roots. The function of CmEXPA4 was further tested by virus-induced gene silencing, and the results showed that CmEXPA4 silencing inhibited the normal development of the chrysanthemum root system. The roots appeared thinner and shorter, and several important root parameters, including total length, average diameter, surface area, total volume, and root tip number, decreased significantly. The cortical cells of the transgenic plant roots were significantly smaller and shorter than those of the control. Collectively, our results demonstrated that CmEXPA4 gene plays a key role in the growth and development of chrysanthemum roots and affects the root system by acting on the individual cells.

Inactive auxin conjugates are accumulated in plants and hydrolyzed to recover phytohormone action. A family of metallopeptidase orthologues has been conserved in Plantae to help regulate auxin homeostatic levels during growth and development. This hydrolase family was recently traced back to liverwort, the most ancient extant land plant lineage. Liverwort’s auxin hydrolase has little activity against auxin conjugate substrates and does not appear to actively regulate auxin. This finding, along with data that shows moss can synthesize auxin conjugates, led to examining another bryophyte lineage, Physcomitrella patens. We have identified and isolated three M20D hydrolase paralogues from moss. The isolated enzymes strongly recognize and cleave a variety of auxin conjugates, including those of indole butyric and indole propionic acids. These P. patens hydrolases not only appear to be “cryptic”, but they are likely to have derived from soil bacteria through Horizontal Gene Transfer. Additionally, support is presented that the plant-type M20D peptidase family may have been universally lost from mosses after divergence from the common ancestor with liverwort.

The fungal species Trichoderma is reported to have a significant impact on the growth and physiological performance of rice plants. However, the molecular mechanisms that induce these effects remain unspecified. Using next-generation sequencing technology, this study compared the differential expression of genes in rice seedlings that had been inoculated with Trichoderma asperellum SL2 with the gene expression in seedlings that had no such inoculation. The study showed that many genes related to plant growth enhancement and physiological functioning are differentially expressed in seedlings which have been symbiotically colonized by T. asperellum SL2. In these seedlings, specific genes related to photosynthesis, RNA activity, stomatal activity, and root development were found to be up-regulated as others were down-regulated. Although the exact causal mechanisms at the molecular level remain to be identified, the presence of Trichoderma versus its absence was associated with almost ten times more significant up-regulations than down-regulations for specific genes that have been identified from previous genomic mapping. Such analysis at the molecular level can help to explain observed phenotypic effects at the organismic level, and it begins to illuminate the observed beneficial relationships expressed phenotypically between crop plants and certain symbiotic microbes.

The effects of four liquid modifiers (organic–inorganic composite modifier, inorganic polymer compound modifier, polyacrylate compound modifier, and organic polymer compound modifier) on plant growth, cadmium (Cd) content, photosynthetic parameters and antioxidant enzymes were studied in cotton (Xinluzao) under Cd stress (5 mg kg−1) in a barrel experiment. The results showed that the Cd treatment of soil increased Cd content in cotton and reduced plant height, net photosynthesis rate (Pn), chlorophyll fluorescence parameters, antioxidant enzyme activity, and biomass. However, the application of liquid modifiers alleviated Cd stress, increased plant biomass, and decreased Cd content in plant organs as well as Cd transport coefficients of the stem and cottonseed. At the same time, there was an increase in gas exchange, photosynthetic pigment content, superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) activity in cotton leaves, whereas malondialdehyde content (MDA) decreased. These results suggest a positive role of liquid modifiers in alleviating Cd stress in cotton, which was due to (1) significant reduction in Cd uptake of roots and Cd-transportation to leaves and (2) improvement in the antioxidant activity, which regulated the oxidants to a level under control, minimizing the oxidative damage in cotton.

This experiment was carried out in pots in a greenhouse to evaluate the effects of arbuscular mycorrhizal fungi (Funneliformis mosseae, Rhizophagus intraradices and Rhizophagus fasciculatus) on carob plant performance under different levels of phosphate fertilization. Non-mycorrhizal (NMyc) and mycorrhizal (Myc) carob plants were subjected to three levels of phosphate fertilization, L1 (0 mg P kg−1 soil), L2 (25 mg P kg−1 soil) and L3 (100 mg P kg−1 soil). Results showed that under L1 and L2 P-fertilization levels, arbuscular mycorrhizal symbiosis significantly improved growth and biomass production of carob plants. Moreover, mineral nutrient (P, K, Na and Ca) acquisition, photosynthetic activity (Fv/Fm), stomatal conductance, total chlorophyll content, and soluble sugar accumulation were also strongly improved in Myc plants in comparison with NMyc ones. Under L1 P-fertilization level, Myc plants showed strongly increased acid phosphatase activity in roots and in the rhizospheric soil than NMyc plants. Furthermore, Myc plants maintained high membrane integrity (over 80%) and low hydrogen peroxide (H2O2) and malondialdehyde (MDA) contents, associated with increased activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), guaiacol peroxidase (G-POD), and catalase (CAT) compared to NMyc plants. However, high phosphorus input (L3) negatively affected root colonization and mycorrhizal plant performance. Thus, carob plants associated with Funneliformis mosseae performed best under phosphorus deficiency and were the least sensitive to the variations of phosphorus input levels.

The development of woody plants is related to the continuity of the procambium and cambium. Whether such a continuity is present in plants with successive cambia, especially in those, where the first cambium is formed outside the primary vascular bundles, has not been analyzed so far. Therefore, we studied the development of vascular meristem in Celosia argentea, in which the first and successive cambial cylinders arise outside the primary bundles and, intriguingly, in the literature are interpreted as developmentally independent structures. Our results showed that in C. argentea, the outermost procambial cells maintain their meristematic characteristics during differentiation of vascular bundles and divide periclinally, forming the zone of procambium-derived cells outside the primary bundles. This zone comprises parenchyma cells bordering the bundles, and a continuous ring of the incipient cambial cells neighboring the primary cortex. Later in the development, the ability to preserve the outermost cells in the cambium undifferentiated is repeated during the formation of successive cylinders of cambia. Together, our results clearly point to the developmental continuity of the procambium and successive cambia in C. argentea, despite their seemingly spatial distinctiveness. We postulate that the mechanism demonstrated in C. argentea is universal and orchestrates the development of successive cambia in other plant species.

Soil polluted with heavy metals is a continuous threat to global crop production. The present study deals with growth, biochemical attributes, photosynthetic pigments, antioxidant responses and gyloxalase systems of mustard plants under varying concentrations of nickel (Ni) stress. Ni stress (150 µM) reduced growth (shoot length by 34.46% and root length by 52.49%), chlorophyll (57.63%), gas exchange parameters (PN by 36.84%, A by 55.61%), leaf relative water content (LRWC by 24.34%), and enhanced hydrogen peroxide (H2O2 by3.23 fold) malondialdehyde (MDA by 2.07 fold), and methylglyoxal (MG by 3.32 fold) content. Si (10− 5 M) application ameliorated the negative effects of Ni on growth, chlorophyll content, photosynthetic traits and also elevated the activities of antioxidant enzymes and enzymes associated with the ascorbate glutathione (AsA-GSH) cycle and glyoxylase systems. Nevertheless, Si application to Ni-stressed plants had an additive effect on the enzyme activities of antioxidants and enzymes of AsA-GSH cycle. Exogenous Si supplementation elevated endogenous Si content which decreased root to shoot Ni translocation and maintained optimum osmolyte and secondary metabolite accumulation. We conclude that Si-induced Ni stress tolerance in mustard plants could be correlated with the upregulation of enzymes associated with antioxidant defence, glyoxalase detoxification systems and sufficient primary and secondary osmoprotectant accumulation.

Alpha-tocopherol (α-Toc) is a member of the vitamin E family and is lipid soluble. Its biosynthesis is by the reaction of isopentyl diphosphate and homogentisic acid in plastid membranes. The putative biochemical activities of tocopherols are linked with the formation of tocopherol quinone species, which subsequently undergo degradation and recycling within cells/tissues. α-Toc plays a key role in a variety of plant metabolic processes throughout the ontogeny of plants. It can maintain the integrity and fluidity of photosynthesizing membranes. It can also neutralize lipid peroxy radicals, consequently blocking lipid peroxidation by quenching oxidative cations. It preserves membrane integrity by retaining membranous structural components under environmental constraints such as water deficiency, high salt content, toxic metals, high/low temperatures, and radiations. α-Toc also induces cellular signalling pathways within biological membranes. Its biosynthesis varies during growth and developmental stages as well as under different environmental conditions. The current review primarily focuses on how α-Toc can regulate various metabolic processes involved in promoting plant growth and development under stress and non-stress and how it can effectively counteract the stress-induced high accumulation of reactive oxygen species (ROS). Currently, exogenous application of α-Toc has been widely reported as a potential means of promoting resistance in plants to a variety of stressful environments.

Pigeonpea (Cajanus cajan L.) is a rich source of nutritionally good quality proteins, carbohydrates, minerals, and vitamins. However, environmental stresses adversely affect its productivity. Only limited reports are available on biochemical/physiological responses of pigeonpea under salt stress. The objectives of the present study were to screen pigeonpea germplasm accessions for salt stress tolerance, followed by understanding their biochemical, epigenetic and molecular responses. Based on germination, growth, and vigor of seedlings under salt stress, the most contrasting pair of salt-responsive genotypes (ICP1071- most salt-sensitive, and ICP7- most salt-tolerant) were selected. Three-week-old seedlings subjected to 250 mM NaCl stress for 7 days showed a significant increase in proline and reducing sugar contents in the case of ICP7, whereas a considerable increase in cell wall-degrading enzyme activity and protein oxidation was observed in ICP1071. Superoxide dismutase, peroxidase, and glutathione reductase activity increased considerably in shoots of ICP7. We observed the CcCYP gene to be upregulated in root, whereas CcCDR was upregulated in shoots of the salt-tolerant genotype to provide protection against the stress. The extent of DNA hypomethylation in the contrasting pigeonpea genotypes under salt stress was correlated with their salt tolerance level. Bisulfite sequencing of CcCDR revealed that methylation of three cytosine residues in CHH context in shoots of the ICP7 genotype due to salt stress results in 2.6-fold upregulated expression of the gene. With a 6.8% increase in methylation of the coding region of CcCDR, its expression level increased by 22%. To the best of our knowledge, this is the first report on a comprehensive study of salt-induced biochemical, epigenetic and molecular responses of pigeonpea, which might be useful in the development of improved salt-tolerant variety.

The objective of the work is to evaluate whether Bradyrhizobium sp. SEMIA6144 and Azospirillum brasilense Az39 can be used for inoculation to mitigate the negative effect of water restriction on growth of Arachis hypogaea. In this study, nitrogenase activity was determined by measuring the H2 evolution in an open-flow system, and N and C concentration in plants were determined by Elemental Analyzer. Lipid peroxidation and polyamines (PA) levels were analyzed by HPLC. The results showed that the restrictive water condition (RWC) caused an 80% inhibition of the N fixation rate. Although both single and double inoculation favored peanut growth under RWC, the inoculation with SEMIA6144 was better. Peanut plants have higher numbers of nodules in the roots when inoculated with SEMIA6144 in the absence of Az39, although it was observed that the inoculation with Az39 favored root development thus allowing the appearance of more infection sites in peanut roots. In double inoculation, the demand for N in the peanut was met with greater effectiveness. PAs found in leaves were putrescine, spermidine, and spermine. The results show that SEMIA6144 inoculation reversed the negative effects of RWC on growth and nodulation peanut parameters. Simultaneous application of SEMIA6144 and Az39 improved early nodulation, efficiency in N fixation and total N, thus increasing the tolerance of A. hypogaea to RWC. Our findings provide new insights in the context of mixed inoculation and improvement of peanut production in a limited water environment.

Selenium (Se) results in primary root shortening and the concomitant induction of lateral roots (LRs) (stress-induced morphogenic response, SIMR). Both ethylene (ET) and nitric oxide (NO) are gasotransmitters interacting with each other during plant growth regulation; however, their involvement and interplay in LR growth have not been examined so far. This study investigates the effect of Se on ET and NO levels and interaction in wild-type (WT) and ET insensitive etr1-1 Arabidopsis. In WT, Se at 15 µM concentration triggered LR emergence (LRem) and slight ET level elevation but in etr1-1 Se-induced LR inhibition was accompanied by four-fold ET level increase which can be associated with the increased expression of ACS2 and ACS8. Treatment with ACC + Se decreased LRem and NO level in WT, whereas AVG + Se in the etr1-1 plants resulted in enhanced LRem and increased NO level indicating that ET may inhibit both NO formation and LR emergence in Se-stressed Arabidopsis. The expression of NO-associated genes (NR1, NR2, GSNOR1, GLB1, GLB2), however, did not correlate with NO levels. Application of GSNO together with Se resulted in enhanced LR outgrowth both in WT and in etr1-1, whereas this effect could be reversed by a NO scavenger which indicates the positive regulatory role of NO during LR emergence. Moreover, GSNO has a clear inhibitory and cPTIO has an inducing effect on ET levels. These data indicate for the first time that the antagonistic interplay between ET and NO regulates the emergence of lateral roots in Arabidopsis under Se stress.

Plant-derived smoke is a positive regulator of seed germination and growth with regard to many plant species. Of the several compounds present in plant-derived smoke, karrikinolide or KAR1 (3-methyl-2H-furo[2,3-c]pyran-2-one) is considered to be the major active growth-promoting compound. To test the efficacy of smoke-saturated water (SSW) and KAR1 on carrot (Daucus carota L.), two separate pot experiments were simultaneously conducted in the same environmental conditions. SSW and KAR1 treatments were applied to the plants in the form of aqueous solutions of variable concentrations. Prior to sowing, seeds were soaked in the solutions of SSW (25.8 µg L−1, 51.6 µg L−1,103.2 µg L−1 and 258.0 µg L−1) and KAR1 (0.015 µg L−1, 0.150 µg L−1, 1.501 µg L−1 and 15.013 µg L−1). Percent seed germination, vegetative growth, photosynthesis and nutritional values were the major parameters through which the plant response to the applied treatments was investigated. The results obtained indicated a significant improvement in all the plant attributes studied. In general, SSW (51.6 µg L−1) and KAR1 (1.501 µg L−1) proved optimum treatments for most the parameters. As compared to the control, 51.6 µg L−1 of SSW and 1.501 µg L−1 of KAR1 increased the percent seed germination by 58.0% and 54.4%, respectively. Over the control, the values of plant height and net photosynthetic rate were enhanced by 33.9% and 40.9%, respectively, due to 51.6 µg L−1 of SSW, while the values of these parameters were increased by 25.2% and 34.0%, respectively, due to 1.501 µg L−1 of KAR1. In comparison with the control, treatment 51.6 µg L−1 of SSW increased the contents of β-carotene and ascorbic acid by 32.7% and 37.9%, respectively, while the treatment 1.501 µg L−1 M of KAR1 enhanced these contents by 42.0% and 48.4%, respectively. This study provides an insight into an affordable and feasible method of crop improvement.

To investigate the effects of nanofertilizers and biofertilizers on the morpho-physiological and biochemical traits of safflower under full irrigation and water deficit stress, this study was carried out as a split-plot experiment based on a Randomized Complete Block Design with three replications at Urmia University in 2015. The main plot was full irrigation (control) and irrigation disruption at heading, flowering, and grain filling stages. Fertilizers, including control (without fertilizer), biofertilizer, water spray, foliar application of nanofertilizers, chemical fertilizers, and combined application of fertilizers, were assigned to the subplot. Plants under full irrigation and combined fertilizers had maximum height and chlorophyll a, whereas the lowest ones were obtained in irrigation disruption at the heading stage and control treatments. The maximum oil content (28.41%) was detected in irrigation disruption at the grain filling stage and nanofertilizer treatment, the lowest (21.96%) was obtained at irrigation disruption at the flowering stage and water spray treatment. The highest proline (397.21 µg g−1 fresh leaf) was found in irrigation disruption at the grain filling stage and water spray treatment, and the lowest (154.68 µg g−1 fresh leaf) was obtained at full irrigation and water spray treatment. Irrigation disruption at the heading stage and control treatments decreased carbohydrate content of fresh leaves by 86.54% compared to full irrigation and the combined fertilizers treatment. Irrigation disruption increases saturated fatty acids (palmitic and stearic acid) and decreases vitamin E and linoleic acid. The combined application of fertilizers significantly increased safflower oil quality. Overall, concerning the obtained highest oil percentage (28.41%), irrigation disruption during grain filling reduced water consumption and application of combined fertilizer via improving oil quality, so it is recommended to farmers.

The two-component system is involved in several developmental events and different responses to the environment. Histidine-containing phosphotransfer proteins (HPs) play a critical role in transferring the phosphoryl group in the nucleus and regulating downstream effectors. Two authentic-HPs (OsAHPs) and three pseudo-HPs (OsPHPs) have been identified in rice. The conserved phosphorylation residue does not occur in OsPHPs, which are proposed as negative regulators in the cytokinin two-component system. One of the OsPHPs, OsPHP3, in rice is highly expressed at root caps. However, the roles of OsPHP3 have not been investigated in rice. We detected two major alternative splicing mRNAs of OsPHP3 and determined the expression in response to different environmental stimuli. The ratio of the two major alternative splicing OsPHP3 variants was significantly altered in response to a light signal and tissue specificity. Additionally, the results also indicated the positive regulation of auxin in the transcription of OsPHP3 in the root, and the ratio of the expression of the two major alternative splicing OsPHP3s was altered. OsPHP3 was also involved in auxin- and cytokinin-regulated lateral root development. Collectively, these results indicate a possible regulation of alternative splicing OsPHP3 isoforms by light and their roles in rice lateral root development.

The objective of this study was to evaluate the ability of the phytohormone S-abscisic acid (S-ABA) to protect maize seedlings grown under drought stress and to measure their increased drought tolerance. The maize hybrids ‘Zhengdan 958’ (ZD958; drought tolerant) and ‘Xundan 20’ (XD20; drought sensitive) were treated with nutrient solutions of different concentrations (1, 2, 4, 8, and 10 mg/kg) of S-ABA under polyethylene glycol (PEG, 15% w/v, MW 6000) simulated drought stress. Optimal concentrations of S-ABA were designed to be sprayed onto the leaves of seedlings, and their effect on endogenous ABA, malondialdehyde (MDA), osmotic substances, antioxidant enzyme activities, and Asr1 gene expression in seedlings were studied. Results indicated that, under drought stress, S-ABA treatment significantly improved maize seed germination rate (GR), germination energy (GE), and seedling biomass (p < 0.05). After spraying 4 mg/kg S-ABA onto leaves, the endogenous hormone ABA, osmotic substances, antioxidant enzyme activities, and expressive quantity of the Asr1 gene were extended and MDA content dropped significantly (p < 0.05). Moreover, ZD 958 endogenous ABA content, osmotic substances content, antioxidant enzyme activity and Asr1 gene expressive quantity were higher than that of XD 20 (p < 0.05). In conclusion, S-ABA treatment increased the content of endogenous ABA, induced an increase in antioxidant enzyme activity and Asr1 gene expression level, reduced the oxidative damage caused by drought to maize leaves, and improved the adaptability of maize seedlings to withstand drought stress. The promoting effect of S-ABA on the drought-tolerant variety ZD 958 was more obvious (p < 0.05). These results serve as a reference for the use of S-ABA in mitigating drought stress in maize.

Vitis vinifera is a species of temperate origin that reactivates the dormant secondary phloem from the previous year at the resumption of growth in spring. Following harsh winters, grapevines may display a set of symptoms including delayed and heterogeneous budbreak, dieback with shoot renewal from the trunk base or sudden death of the plant. Although it was suggested that these symptoms may be associated with freeze damage to the secondary phloem, there is no experimental evidence that quantifies tissue responses to freezing and their consequences for the plant. This work evaluated how different severities of cold damage to the secondary phloem during the dormant season impacted the anatomical, physiological, and agronomic responses of grapevines during the subsequent growing season. Single-node cane sections were subjected to a range of freezing temperatures that damaged only the phloem, and changes in anatomy and physiology were monitored. In addition, the consequences of natural winter freezes for yield formation of field-grown plants were evaluated. Our results suggest that the more severe a freeze event is, the greater will be the degree of secondary phloem disorganization, leading to delays in budbreak and subsequent phenological stages, and in cambial activity. Winter freezes also led to a loss of plant vigor and a reduction in cluster number, berries per cluster, and fruit sugar content. We conclude that winter freeze events can produce hidden damage in grapevine perennial tissues, which may compromise subsequent growth and productivity depending on the severity of the damage.

In the first step in this study, the effect of 50 mM NaCl was studied on germination percentage of five different Lepidium draba (L. draba) ecotypes, and Rafsanjan ecotype was selected as experimental material as it had the highest germination percentage. In the second step, some biochemical, physiological, and morphological traits along with content of sulforaphane (SFN) as well as the expression level of Cytochorome P450 79F1 (CYP79F1) were evaluated in 14-day-old L. draba sprouts that grew 9 days in the presence of various concentrations of NaCl including 0, 25, 50, 75, and 100 mM. According to the results of this study, germination percentage of Rafsanjan ecotype along with lengths of stem and root were declined with increasing concentrations of NaCl. Ascorbate peroxidase, guaiacol peroxidase, and superoxide dismutase enzymes activity increased up to 75 mM NaCl and then decreased. With increasing the doses of NaCl, concentrations of Na+ and Cl− increased, whereas P, Ca2+, and K+ decreased. Also, accumulation of some oxidative stress parameters including electrolyte leakage, malondialdehyde, other aldehydes, and hydrogen peroxide increased with increasing NaCl concentrations in all samples. Furthermore, contents of total phenolic, total flavonoid, total anthocyanin, total free amino acids, and total soluble carbohydrate were induced with the induction of NaCl concentrations. In this study, SFN formation increased with increasing concentration of sodium chloride up to 75 mM and decreased at higher concentration. In the last step, a partial CYP79F1 mRNA and its protein sequence were identified and registered in GenBank and then changes in the CYP79F1 gene expression levels under 0, 25, 50, 75, and 100 mM NaCl were calculated. The gene expression levels of CYP79F1 also showed the same pattern as was seen for SFN formation under salinity stress.

CONSTANS (CO) and CONSTANS-like (COL) are two centrally important flowering-related genes in the photoperiodic pathway of Cymbidium, an economically important orchid genus within the Orchidaceae. To assess how photoperiod affects flowering in three Cymbidium species, CsCOL1, CgCOL, and CeCOL were isolated and characterized from Cymbidium sinense, Cymbidium goeringii, and Cymbidium ensifolium, respectively. CsCOL1, CgCOL, and CeCOL, which contain a CCT domain and two conserved B-box zinc fingers, belong to Group Ic in the CO/COL protein family. These three genes, which were expressed in all organs, especially in the leaves, exhibited the same diurnal rhythm and were abundant in the late light period under long days (LD). However, their diurnal oscillation rhythm under short days (SD) differed. CsCOL1 was highly transcribed in the late dark period under SD. CeCOL was rapidly suppressed in the light, increased in the dark, and peaked at the end of the dark period under SD. CgCOL expression gradually increased, peaking after 4 h of darkness under SD. When CsCOL1 and CeCOL were overexpressed in Arabidopsis under LD, flowering was promoted, suggesting that CsCOL1 and CeCOL may be floral inducers in C. sinense and C. ensifolium, respectively. The overexpression of CgCOL delayed flowering in Arabidopsis, suggesting that it may act as a floral repressor in C. goeringii. This study provides greater insight into the molecular mechanisms regulating flowering time in three Cymbidium species, specifically related to photoperiod. This has practical implications for controlled flower production in potted Cymbidium greenhouse production systems.

Ascorbate is an antioxidant in plants. Its content is an important index to evaluate the nutritional quality of celery. In higher plant, ascorbate accumulation is effected by CO2 concentration. To study the effects of elevated CO2 (1000 µmol mol−1) on ascorbate accumulation in celery, ascorbate contents and the transcript levels of genes related to ascorbate metabolism in the leaves (leaf blade and petiole) were detected. The results of current study showed that the ascorbate and total ascorbate levels increased during all the treated stages in celery petioles, and they were 1.09–3.91 fold of the control. In leaf blades, the ascorbate contents exhibited a lower level (96.12% and 90.46% of the control) in treatments at 2 and 4 days, and then increased to 1.04 and 1.27 fold of the control in treatments at 6 and 8 days, respectively. Elevated CO2 altered the expression profiles of ascorbate-related genes and the activities of corresponding enzymes. Expression levels of the genes, AgPGI2, AgGMP, AgPMI, AgGalDH, AgGalLDH, GalUR, AgDHAR1, AgAPX1, and AgAO, in the leaf blades corresponded well to the change in ascorbate contents. At 6 days of treatment, the relative expression levels of AgPGI2, AgPMI, AgGGP1, AgGGP2, AgGalUR, AgMDHAR, AgDHAR1, and AgAPX1 in leaf blades increased, and were 4.41, 2.39, 4.65, 3.64, 3.11, 4.53, 4.59, and 3.86 times higher than that of the control. Increased ascorbate accumulation in celery leaves under elevated CO2 treatments might be also related to the change in SOD, POD, and CAT activities, as well as GSH content. These results will enhance our understanding on the effects of elevated CO2 on ascorbate accumulation and potential molecular mechanism regulating ascorbate metabolism in celery.

Differential growth of plants in response to the changes in the light and gravity vectors requires a complex signal transduction cascade. Although many of the details of the mechanisms by which these differential growth responses are induced are as yet unknown, auxin has been implicated in both gravitropism and phototropism. Specifically, the redistribution of auxin across gravity or light-stimulated tissues has been detected and shown to be required for this process. The approaches by which auxin has been implicated in tropisms include isolation of mutants altered in auxin transport or response with altered gravitropic or phototropic response, identification of auxin gradients with radiolabeled auxin and auxin-inducible gene reporter systems, and by use of inhibitors of auxin transport that block gravitropism and phototropism. Proteins that transport auxin have been identified and the mechanisms which determine auxin transport polarity have been explored. In addition, recent evidence that reversible protein phosphorylation controls this process is summarized. Finally, the data in support of several hypotheses for mechanisms by which auxin transport could be differentially regulated during gravitropism are examined. Although many details of the mechanisms by which plants respond to gravity and light are not yet clear, numerous recent studies demonstrate the role of auxin in these processes.

Rapid-cycling Brassica populations were initially developed as a model for probing the genetic basis of plant disease. Paul Williams and co-workers selected accessions of the six main species for short time to flower and rapid seed maturation. Over multiple generations of breeding and selection, rapid-cycling populations of each of the six species were developed. Because of their close relationship with economically important Brassica species, rapid-cycling Brassica populations, especially those of B. rapa (RCBr) and B. oleracea, have seen wide application in plant and crop physiology investigations. Adding to the popularity of these small, short-lived plants for research applications is their extensive use in K-12 education and outreach.

Evidence is accumulating implicating cortical microtubules in the directional control of cell expansion. However, the role of actin filaments in this process is still uncertain. To determine the involvement of actin in cell elongation, the organization of actin filaments in primary roots of maize (Zea mays L.) was examined by use of an improved fluorochrome-conjugated phalloidin-labeling method. With this method, a previously undetected state of actin organization was revealed in the elongation and maturation zone of maize roots. Fine transversely oriented cortical actin was observed in all cells of the elongation zone, including the epidermis, cortex, and vascular tissues. The orientation of cortical actin shifted from a predominantly transverse orientation to oblique, longitudinal, and/or random arrangements as the cells matured. The reorientation of cortical actin in maturing root cells mimics the behavior of cortical microtubules reported in other studies. Furthermore, roots treated with the microtubule-stabilizing drug taxol improved the quality of actin preservation as evidenced by the thicker bundles of cortical actin. This suggested that taxol was also capable of stabilizing the cortical actin networks. The elongation of roots exposed to 1 micromole Latrunculin B, an actin-disrupting drug, was inhibited, and after 24 h the roots exhibited moderate swelling particularly along the elongation zone. Latrunculin B also caused microtubules to reorient from transverse to oblique arrays. The results from this study provide evidence that cortical microtubules and actin filaments respond in a coordinated way to environmental signals and may well depend on both elements of the cytoskeleton.

We studied the effect of 4,4,4-trifluoro-3-(indole-3-)butyric acid (TFIBA), a recently described root growth stimulator, and 5,6-dichloro-indole-3-acetic acid (DCIAA) on growth and microtubule (MT) organization in roots of Lactuca sativa L. DCIAA and indole-3-butyric acid (IBA) inhibited root elongation and depolymerized MTs in the cortex of the elongation zone, inhibited the elongation of stele cells, and promoted xylem maturation. Both auxins caused the plane of cell division to shift from anticlinal to periclinal. In contrast, TFIBA (100 micromolar) promoted elongation of primary roots by 40% and stimulated the elongation of lateral roots, even in the presence of IBA, the microtubular inhibitors oryzalin and taxol, or the auxin transport inhibitor naphthylphthalamic acid. However, TFIBA inhibited the formation of lateral root primordia. Immunostaining showed that TFIBA stabilized MTs orientation perpendicular to the root axis, doubled the cortical cell length, but delayed xylem maturation. The data indicate that the auxin-induced inhibition of elongation and swelling of roots results from reoriented phragmoplasts, the destabilization of MTs in elongating cells, and promotion of vessel formation. In contrast, TFIBA induced promotion of root elongation by enhancing cell length, prolonging transverse MT orientation, delaying cell and xylem maturation.

In shoots, polar auxin transport is basipetal (that is, from the shoot apex toward the base) and is driven by the basal localization of the auxin efflux carrier complex. The focus of this article is to summarize the experiments that have examined how the asymmetric distribution of this protein complex is controlled and the significance of this polar distribution. Experimental evidence suggests that asymmetries in the auxin efflux carrier may be established through localized secretion of Golgi vesicles, whereas an attachment of a subunit of the efflux carrier to the actin cytoskeleton may maintain this localization. In addition, the idea that this localization of the efflux carrier may control both the polarity of auxin movement and more globally regulate developmental polarity is explored. Finally, evidence indicating that the gravity vector controls auxin transport polarity is summarized and possible mechanisms for the environmentally induced changes in auxin transport polarity are discussed.

Recent studies on a variety of organisms point to the ubiquity of RNA interference (RNAi) as a means to induce a gene-specific block to translation. RNAi has gained popularity in the last few years in the study of a number of problems in development. In this review, we highlight recent findings with RNAi using several different kinds of animals and fungi, and we show how these responses parallel cosuppression effects described in plants nearly a decade earlier. We then point to the efficacy of RNAi in studying minor and regulatory components of the plant cytoskeleton, and we highlight some recent studies using this approach with the water fern, Marsilea vestita.

Ceratopteris richardii is an aquatic fern grown in tropical and subtropical regions of the world. It is proven to be a productive model system for studies in the genetics, biochemistry, and cell biology of basic biologic processes that occur in early gametophytic development. It provides several advantages to biologists, especially those interested in gravitational biology, polarity development, and in the genetics of sexual development. It is easy to culture, has a relatively short life cycle, and offers an array of attractive features that facilitate genetic studies. The germination and early development of large populations of genetically identical spores are easy to synchronize, and both the direction of polarity development and cell-level gravity responses can be measured and readily manipulated within the first 24 h of spore development. Although there is no reliable transformation system available yet in Ceratopteris, recent studies suggest that the technique of RNA interference can be used to block translation of specific genes in a related fern, Marsilea, and current studies will soon reveal the applicability of this approach, as well as of other transformation approaches, in Ceratopteris. A recently completed expressed sequence tag (EST) sequencing project makes available the partial sequence of more than 2000 cDNAs, representing a significant percentage of the genes being expressed during the first 24 h of spore germination, when many developmentally interesting processes are occurring. A microarray of these ESTs is being constructed, so especially for those scientists interested in basic cellular phenomena that occur early in spore germination, the availability of the ESTs and of the microarray will make Ceratopteris an even more attractive model system.

A computer-based video digitizer system is described which allows automated tracking of markers placed on a plant surface. The system uses customized software to calculate relative growth rates at selected positions along the plant surface and to determine rates of gravitropic curvature based on the changing pattern of distribution of the surface markers. The system was used to study the time course of gravitropic curvature and changes in relative growth rate along the upper and lower surface of horizontally-oriented roots of maize (Zea mays L.). The growing region of the root was found to extend from about 1 mm behind the tip to approximately 6 mm behind the tip. In vertically-oriented roots the relative growth rate was maximal at about 2.5 mm behind the tip and declined smoothly on either side of the maximum. Curvature was initiated approximately 30 min after horizontal orientation with maximal (50 degrees) curvature being attained in 3 h. Analysis of surface extension patterns during the response indicated that curvature results from a reduction in growth rate along both the upper and lower surfaces with stronger reduction along the lower surface.

Leaf-sheath pulvini of excised segments from oat (Avena sativa L.) were induced to grow by treatment with 10 micromoles indole-3-acetic acid (IAA), gravistimulation, or both, and the effects of calcium, EGTA, and calcium channel blockers on growth were evaluated. Unilaterally applied calcium (10 mM CaCl2) significantly inhibited IAA-induced growth in upright pulvini but had no effect on growth induced by either gravity or gravity plus IAA. Calcium alone had no effect on upright pulvini. The calcium chelator EGTA alone (10 mM) stimulated growth in upright pulvini. However, EGTA had no effect on either IAA- or gravity-induced growth but slightly diminished growth in IAA-treated gravistimulated pulvini. The calcium channel blockers lanthanum chloride (25 mM), verapamil (2.5 mM), and nifedipine (2.5 mM) greatly inhibited growth as induced by IAA (> or = 50% inhibition) or IAA plus gravity (20% inhibition) but had no effect on gravistimulated pulvini. Combinations of channel blockers were similar in effect on IAA action as individual blockers. Since neither calcium ions nor EGTA significantly affected the graviresponse of pulvini, we conclude that apoplastic calcium is unimportant in leaf-sheath pulvinus gravitropism. The observation that calcium ions and calcium channel blockers inhibit IAA-induced growth, but have no effect on gravistimulated pulvini, further supports previous observations that gravistimulation alters the responsiveness of pulvini to IAA.

The influence of putrescine (Put) and AgNO(3) on shoot multiplication, in vitro flowering and endogenous titers of polyamines in Cichorium intybus L. cv. Lucknow local was investigated. Exogenous administration of Put at a concentration of 40 mM resulted in maximum tissue response in terms of shoot numbers (34.6 +/- 2.61) and shoot lengths (7.6 +/- 0.57 cm) on MS media supplemented with 2-iP (2.0 mg L(-1)) and GA(3) (0.5 mg L(-1)) as observed on the 35(th) day. Exogenous application of 40 µM AgNO(3) resulted in maximum shoot number (36.8 +/- 2.63) and shoot lengths (7.9 +/- 0.76 cm) on day 35 on the same media. Endogenous titers of conjugated spermidine decreased sharply from day 7-21, whereas endogenous conjugated spermine levels peaked on day 28 (1265 +/- 94.9 nmoles g(-1) FW), after treatment with 40 mM Put. Whereas, AgNO(3) (40 µM) fed samples resulted in higher titers of endogenous conjugated spermine (1405 +/- 105.6 nmoles g(-1) FW, 3.62 fold over control) on day 14. All other treatments showed decreasing endogenous levels during the whole culture period. Both Put (40 mM) and AgNO(3) (40 µM) resulted in floral initiation and floral development on day 28 and 14 (3.76 +/- 0.16, 4.2 +/- 0.21 flowers per shoot apices), respectively. To investigate the role of Put (40 mM) and AgNO(3) (40 µM) on morphogenetic response and endogenous conjugated polyamine titers in shoots of chicory, polyamine inhibitors (DFMA and DFMO) were used. The morphogenetic response and the endogenous conjugated pool of polyamines were diminished in DFMA and DFMO treatments, but could be restored by addition of Put (40 mM) and AgNO(3) (40 µM). Under exogenous Put feeding, ethylene production was reduced in shoot cultures of chicory. This study shows for the first time the influence of polyamines on multiple shoot initiation from axillary buds of C. intybus L. cv. Lucknow local and also indicates the promotive effect of Put and AgNO(3) on autoregulation of polyamine biosynthesis, thereby regulating in vitro flowering, the endogenous pool of polyamines and shoot multiplication.

The effect of purine (BA) and phenylurea (CPPU) cytokinins on apical dominance release in in vitro cultured Rosa hybrida L., cv. Madelon and Motrea was evaluated. Cv. Madelon shows stronger natural apical growth and fewer branches than cv. Motrea in vivo and in vitro. We examined the effects under three conditions, without the addition of the auxin IBA, in the presence of IBA, and in material pretreated with a pulse of IBA. Results were scored weekly for 4 weeks. BA and CPPU stimulated axillary bud break, and higher numbers of open buds were recorded in the presence of CPPU. When CPPU cytokinin was added to culture medium, physiologic features such as bud sprouting and shoot fresh and dry weight were enhanced. CPPU was also highly efficient for overcoming IBA inhibition of bud outgrowth. Different cultivar responses were observed.

Parasitic strategies within the angiosperms generally succeed by tightly coupling developmental transitions with host recognition signals in a process referred to as xenognosis. Within the Scrophulariaceae, Striga asiatica is among the most studied and best understood parasitic member with respect to the processes of host recognition. Specific xenognosins regulate seed germination, the development of the host attachment organ, the haustorium, and several later stages of host-parasite integration. Here we discuss the signals regulating the development of the haustorium, the critical vegetative/parasitic transition in the life cycle of this obligate parasite. We provide evidence for the localized production of H(2)O(2) at the Striga root tip and suggest how this oxidant is used to exploit host peroxidases and cell wall pectins to generate a simple benzoquinone signal. This benzoquinone xenognosin proves to be both necessary and sufficient for haustorial induction in cultured seedlings. Furthermore, evidence is provided that benzoquinone binding to a redox active site completes a "redox circuit" to mediate signal perception. This redox reaction regulates the time-dependent expression of specific marker genes critical for the development of the mature host attachment organ. These studies extend the emerging series of events necessary for the molecular regulation of organogenesis within the parasitic plants and suggest novel signaling features and molecular mechanisms that may be common across higher plants.

Plant responses to herbivores are complex. Genes activated on herbivore attack are strongly correlated with the mode of herbivore feeding and the degree of tissue damage at the feeding site. Phloem-feeding whiteflies and aphids that produce little injury to plant foliage are perceived as pathogens and activate the salicylic acid (SA)-dependent and jasmonic acid (JA)/ethylene-dependent signaling pathways. Differential expression of plant genes in response to closely related insect species suggest that some elicitors generated by phloem-feeding insects are species-specific and are dependent on the herbivore's developmental stage. Other elicitors for defense-gene activation are likely to be more ubiquitous. Analogies to the pathogen-incompatible reactions are found. Chewing insects such as caterpillars and beetles and cell-content feeders such as mites and thrips cause more extensive tissue damage and activate wound-signaling pathways. Herbivore feeding is not equivalent to mechanical wounding. Wound responses are a part of the induced responses that accompany herbivore feeding. Herbivores induce direct defenses that interfere with herbivore feeding, growth and development, fecundity, and fertility. In addition, herbivores induce an array of volatiles that creates an indirect mechanism of defense. Volatile blends provide specific cues to attract herbivore parasites and predators to infested plants. The nature of the elicitors for volatile production is discussed.

Plant parasitic nematodes are ubiquitous and cosmopolitan pathogens of vascular plants and exploit all parts of the roots and shoots, causing substantial crop damage. Nematodes deploy a broad spectrum of feeding strategies, ranging from simple grazing to the establishment of complex cellular structures (including galls) in host tissues. Various models of feeding site formation have been proposed, and a role for phytohormones has long been speculated, although whether they perform a primary or secondary function is unclear. On the basis of recent molecular evidence, we present several scenarios involving phytohormones in the induction of giant cells by root-knot nematode. The origin of parasitism by nematodes, including the acquisition of genes to synthesize or modulate phytohormones also is discussed, and models for horizontal gene transfer are presented.

The term "actinorhiza" refers both to the filamentous bacteria Frankia, an actinomycete, and to the root location of nitrogen-fixing nodules. Actinorhizal plants are classified into four subclasses, eight families, and 25 genera comprising more than 220 species. Although ontogenically related to lateral roots, actinorhizal nodules are characterized by differentially expressed genes, supporting the idea of the uniqueness of this new organ. Two pathways for root infection have been described for compatible Frankia interactions: root hair infection or intercellular penetration. Molecular phylogeny groupings of host plants correlate with morphologic and anatomic features of actinorhizal nodules. Four clades of actinorhizal plants have been defined, whereas Frankia bacteria are classified into three major phylogenetic groups. Although the phylogenies of the symbionts are not fully congruent, a close relationship exists between plant and bacterial groups. A model for actinorhizal specificity is proposed that includes different levels or degrees of specificity of host-symbiont interactions, from fully compatible to incompatible. Intermediate, compatible, but delayed or limited interactions are also discussed. Actinorhizal plants undergo feedback regulation of symbiosis involving at least two different and consecutive signals that lead to a mechanism controlling root nodulation. These signals mediate the opening or closing of the window of susceptibility for infection and inhibit infection and nodule development in the growing root, independently of infection mechanism. The requirement for at least two molecular recognition steps in the development of actinorhizal symbioses is discussed.

Under nitrogen-limiting conditions, bacteria from the family Rhizobiaceae establish a symbiosis with leguminous plants to form nitrogen-fixing root nodules. These organs require a coordinated control of the spatiotemporal expression of plant and bacterial genes during morphogenesis. Both plant and bacterial signals are involved in this regulation in the plant host. Plant genes induced during nodule development, the so-called nodulin genes, have been extensively characterized. Products of several of these genes show homologies to known regulators of signal transduction pathways in other plant or animal systems. Initial functional analysis of the molecular mechanisms implicated in nodulation have been undertaken using model legumes. Insertion mutagenesis and transgenic technologies to modify nodulin gene expression, as well as pharmacologic approaches, have been used to analyze molecular mechanisms involved in morphologic responses induced by the bacterial symbiont in the plant. G protein-mediated transduction mechanisms have been implicated, and the nin transcription factor appears to be required for early steps in nodule development. ENOD40, a gene coding for an RNA that contains only short ORFs, seems to be closely tied to nodule primordium formation. In addition, a vascular-associated Krüppel-like transcription factor and small Rab type G-proteins affect bacteroid differentiation and the function of the nitrogen-fixing zone. These initial results presage a wealth of information that will be obtained from the application of genomic approaches to legumes.

Most land plant species that have been examined exist naturally with a higher fungus living in and around their roots in a symbiotic partnership called a mycorrhiza. Several types of mycorrhizal symbiosis exist, defined by the host/partner combination and the morphology of the symbiotic structures. The arbuscular mycorrhiza (AM) is ancient and may have co-evolved with land plants. Emerging results from gene expression studies have suggested that subsets of AM genes were co-opted during the evolution of other biotrophic symbioses. Here we compare the roles of phytohormones in AM symbiosis and ectomycorrhizas (EC), a more recent symbiosis. To date, there is little evidence of physiologic overlap between the two symbioses with respect to phytohormone involvement. Research on AM has shown that cytokinin (CK) accumulation is specifically enhanced by symbiosis throughout the plant. We propose a pathway of events linking enhanced CK to development of the AM. Additional and proposed involvement of other phytohormones are also described. The role of auxin in EC symbiosis and recent research advances on the topic are reviewed. We have reflected the literature bias in reporting individual growth regulator effects. However, we consider that gradients and ratios of these molecules are more likely to be the causal agents of morphologic changes resulting from fungal associations. We expect that once the individual roles of these compounds are explained, the subtleties of their function will be more clearly addressed.

Plants accumulate a diverse array of natural products, which can serve either to defend the plant against various microbes in its environment or to attract various microbes, both beneficial and pathogenic. Plants must also attract pollinators, repel or poison herbivores, compete with other plant species, and protect themselves from environmental dangers such as high light intensities. Some compounds have been implicated in playing a role in multiple interactions. Although the structures vary immensely in size and complexity, most are derived from a limited number of core biosynthetic pathways. This review briefly summarizes the biosynthetic origins of phenylpropanoid (including simple phenolics, flavonoids, anthocyanins and isoflavonoids), polyacetate, terpenoid, and alkaloid classes of metabolites. Compounds reported to be important in plant-microbe, plant-animal, and plant-plant interactions will be given as examples of each of these classes. Other aspects of biosynthesis also will be discussed, including the timing or location of biosynthesis, the potential for genetic manipulation of these pathways, and various questions regarding the biosynthesis of these compounds.

The legume-Rhizobium symbiosis and that between Euprymna scolopes and Vibrio fischeri show some surprising physiological similarities as well as differences. Both interactions rely on exchange of signal molecules, some of which are derived from bacterial cell surface molecules. Although the legume-Rhizobium symbiosis is nutritionally based as are many animal-microbe symbioses, it is not obligate because the plant initiates nodule formation only when the soil is deficient in nitrogen. In contrast, the squid-Vibrio symbiosis is obligate for the squid but is not nutritionally based. Rather, the bacteria produce light, which enables the animal to evade predators. These similarities and differences are described and discussed in term of the overall question of whether or not these two symbiotic relationships have evolved from commensal or pathogenic/parasitic interactions between prokaryotes and eukaryotes.

The role of abscisic acid (ABA) in banana fruit ripening was examined with the ethylene binding inhibitor, 1-methylcyclopropene (1-MCP). ABA (0, 10(-5), 10(-4), or 10(-3) mol/L) was applied by vacuum infiltration into fruit. 1-MCP (1 µL/L) was applied by injecting a measured volume of stock gas into sealed glass jars containing fruit. Fruit ripening, as judged by ethylene evolution and respiration associated with color change and softening, was accelerated by 10(-4) or 10(-3) mol/L ABA. ABA at 10(-5) mol/L had no effect. The acceleration of ripening by ABA was greater at 10(-3) mol/L than at 10(-4) mol/L. ABA-induced acceleration of banana fruit ripening was not observed in 1-MCP treated fruit, especially when ABA was applied after exposure to 1-MCP. Thus, ABA's promotion of ripening in intact banana fruit is at least partially mediated by ethylene. Exposure of ABA-treated fruit to 0.1 µL/L ethylene for 24 h resulted in increased ethylene production and respiration, and associated skin color change and fruit softening. Control fruit (no ABA) was unresponsive to similar ethylene treatments. The data suggest that ABA facilitates initiation and progress in the sequence of ethylene-mediated ripening events, possibly by enhancing the sensitivity to ethylene.

A "double-water-film electrode technique" has been developed for the long-term characterization of the electrical properties across the interface between the nodal (N) and internodal (A or B) cells and the vacuole along the length of an internode of Chara as a function of time and temperature. The electrode unit consisted of a pair of the water-film electrodes described elsewhere (Chilcott 1988; Chilcott and others 1983; Coster and others 1984; Lucas 1985; and Ogata 1983). The distance between two water-film probes was fixed at 1.0 cm. By scanning the electrode unit, the spatial variations in electrical resistance and capacitance along the longitudinal axis of Chara were observed. Analysis was performed by applying an electrical equivalent circuit for the biomembrane (Philippson 1921). Across the internode (-A or -B)/central nodal cells interface, the specific parallel resistance (Rm) and the parallel capacitance (Cm) at 20 degrees C were 30 +/- 5 x 10(-3) Omegam(2) and 1.5 +/- 0.5 x 10(-1)Fm(-2) (at 30 Hz), respectively. And the series resistance, corresponding to the vacuole of the internode was 8 x 10(-3) Omegam(2). Study of temperature dependencies of Rm and Cm suggested that a dynamic homeostatic regulation was operating at the interface where numerous plasmodesmata were observed with an electron microscope (Pickett-Heaps 1967; Spanswick and Costerton 1967). Assuming that the individual cylinder of plasmodesma was filled only with cytoplasm, the number of plasmodesma per interface was estimated at 2.6 x 10(5).

Two methods of analyses were used to investigate tooth development in serrate (se) mutant and wild-type Columbia-1 (Col-1) Arabidopsis thaliana leaves. There were almost twice as many teeth with deeper sinuses and two orders of toothing on the margins of serrate compared with Columbia-1 leaves. The main objective of this study was to test three hypotheses relative to the source of polymorphism in tooth development: (i) Teeth share similar growth rates and initial sizes, but the deeper teeth are initiated earlier in leaf development. (ii) Teeth share similar timing of initiation and growth rates, but the deeper teeth have a larger initial size. (iii) Teeth share similar timing of initiation and initial sizes, but the deeper teeth have a faster growth rate. Leaf plastochron index (LPI) was used as the time variable for leaf development. Results showed teeth in se were initiated at -27 LPI, 15 plastochrons earlier than those of Col-1. Serrate leaf expansion was biphasic, with the early phase expanding at half the relative plastochron rate of the later phase, which equaled the constant relative expansion rate of Col-1 leaves. Allometric analyses of tooth development obscured the interactions between time of tooth and leaf initiation and the early phase of leaf expansion characteristic of serrate leaves and teeth. Timing of developmental events that allometric analysis obscured can be readily detected with the LPI as a developmental index.

The effects of sandy soil pH on the distribution of growth velocities and on cation concentrations and deposition rates in root growth zones of Zea mays L. seedlings were investigated. The pH values of the rooting medium varied between 4.2 and 8.6 in sand culture (70% saturated) without external supply of nutrients. At all pH values, densities (in µmoles per g fresh weight) of potassium, magnesium, and calcium increased toward the root tip. Lower pH in the medium increased calcium tissue density fivefold and magnesium density 1.7-fold, whereas the density of potassium, the overall elongation rate, and the growth velocity distribution did not show any significant pH dependence. Throughout the growth zone the deposition rates of the divalent cations, as calculated on the basis of the continuity equation, increased with lower pH. The data are consistent with the hypothesis that the effects of pH on the cation deposition rates are due to the increase in the divalent cation concentration of the soil solution at low pH and that the abundant uronic acid residues of the young walls of the meristem provide a reservoir of storage capacity for Ca and Mg under conditions of low nutrient availability.

Drift of mutated sectors in sectorial or mericlinal plant chimeras has been interpreted as indirect evidence of initial impermanence at the apex. However, the same effect may result from mutation in noninitial cells positioned close to the vertex of the apical dome. Clonal analysis of the cell packets present in the superficial layer of spruce and magnolia apices provided the library of patterns suggesting that the position and the number of initial cells, and in some cases also the meristem axis inclination, may change over time. Multicellular clones originating from a single cell have been found in the geometric center of some apices, whereas in other apices the cellular center (where three or four clonal borders meet) did not correspond to the geome