Effect of symbiosis with arbuscular mycorrhizal fungi on salt stress tolerance in GF677 (peach×almond) rootstock
Introduction
Salinity is one of the most damaging degradation processes affecting agricultural soils, especially in arid and semi-arid regions. In these areas salinization is considered as one of the major causes of soil desertification (Romero-Munar et al., 2019). Unfortunately, observed soil salinity is rapidly increasing with an estimated increment of 0.3–1.5 million ha of farmland per year and consequently, crop production is decreasing by more than 20 % (Evelin et al., 2019). In saline soils, high concentrations of specific ions like sodium and chloride display toxic effects on plants by increasing reactive oxygen species (ROS) levels, disturbing the structure of macromolecules (especially enzymes), damaging cell organelles and membranes, causing metabolic disorders, impaired nutrient uptake, decreased nutrient transport to the shoot, disrupting photosynthesis and respiration, finally restricting plant growth and development (Amanifar et al., 2019; Porcel et al., 2016). However, nonhazardous biological approaches involving symbiotic microorganisms, like rhizobacteria and mycorrhizal fungi, in combination with cultivation of moderately salt-tolerant plants, seems to be able to mitigate negative effects of salinity stress (Bencherif et al., 2019). Recent research showed that arbuscular mycorrhizal fungi (AMF) could facilitate plant salinity tolerance by forming mutualistic relationships with plants and enhancing plant growth and yield under salt stress (Ye et al., 2019). Somehow symbiosis with AMF enables increased phosphorus uptake in root (Romero-Munar et al., 2019), higher K+/Na + ratios in plant tissues and accumulation of compatible solutes (like proline, glycine betaine or soluble sugars) which facilitate better osmotic adjustment, improved photosynthetic and water use efficiency in symbiotic plants exposed to salt stress. Furthermore, symbiosis with AMF enhances activity of antioxidant enzymes (like superoxide dismutase (SOD), catalases (CAT), ascorbate peroxidase (APX), monodehydro ascorbate reductase (MDHAR), dehydro ascorbate reductase (DHAR), etc.), which are necessary to cope with reactive oxygen species (ROS) generated by salinity (Li et al., 2017; Porcel et al., 2012; Romero-Munar et al., 2019; Wu et al., 2016). However, even though the association with AMF often enhances growth and yield of host plants by increasing their tolerance to salt stress (Kumar et al., 2014), its effect highly depends on the type of host plant and fungal species (Amanifar et al., 2019).
Understanding physiological and molecular mechanisms involved in plant-fungi symbiosis under abiotic stresses is of high importance to enable application of AMF bioprotective property in raising plant tolerance to abiotic stresses (Singh et al., 2011). Plants responses to combined mycorrhiza symbiosis and salt stress have been analyzed in several studies (mostly related to crops physiology) (Kumar et al., 2014; Bencherif et al., 2019). Little attention has been given to the effect of AMF on salt stress tolerance in trees, especially at molecular level. Since trees are of great significance for numerous reasons (i.e. for providing main life’s essentials like food and oxygen, preventing land erosion and air pollution, etc.), shedding more light to this subject is an important task. Genus Prunus comprising ca. 430 species of trees and shrubs, majority of which are of considerable agricultural and horticultural importance (cultivated for edible seeds and fruits, ornamental qualities, timber) (Poonam et al., 2012), also contains species sensitive to salt stress. Most of the stone fruits and almonds display sensitivity to salt concentrations above 1.5 dS m−1, which can cause yield reduction for ca. 50 % at salt concentration of 4 dS m−1 (Dejampour et al., 2012). In the modern fruit production rootstocks represent essential component used for cultivars adaptation to diverse environmental conditions and cultural practices. Moreover, rootstocks display several traits that are absent in the scion, such as resistance to soil’s pest and disease, better anchorage, improved nutrient uptake as well as better tolerance to drought, high salinity or other limiting soil conditions (Muñoz et al., 2015). One of the economically important rootstock used in almond and peach production is GF677. This rootstock was produced in 1965 by Bernhard as a hybrid of Prunus dulcis × Prunus persica at the Grand Ferrad Research Station, France. It displays the ability of adaptation to poor soil fertility and drought conditions (Nezami et al., 2014; Tsipouridis and Thomidis, 2017; Baránek et al., 2019), which along with its economic importance makes GF677 an excellent candidate for testing the effect of AMF symbiosis on tree’s salinity stress tolerance. In this research we examined the most important physiological parameters of GF677 rootstock response to combined mycorrhiza inoculation and exposure to different salt concentrations. Bioinformatics analysis of freely available online data was used to identify genes common to AMF symbiosis and salt stress response. Among genes identified as common for both responses, two most prominent ones were selected for the expression analysis in leaves and roots of GF677 plants inoculated/not inoculated with AMF under the salt stress/without salt stress. Obtained results are discussed in the light of effects of symbiosis with arbuscular mycorrhiza fungi on alleviation of salt stress impact in GF677 plants.
Section snippets
Plant, soil and fungi materials
GF677 rootstocks, obtained from Dr. Nourbakhsh's nursery greenhouse (Saman County, Iran), were propagated through single node cuttings. Soil collected from the village of Chelvan (32°29′15.56′'N;50°55′49.75′'E) in Saman County, Chaharmahal va Bakhtiari Province, Iran, was used for research upon its 2 mm sieving. Some of the physical and chemical properties of this soil were previously determined using conventional laboratory methods (Aghababaei et al., 2014). Two species of AMF were used for
Physiological and biochemical analysis
Inoculation of GF677 plants with arbuscular mycorrhiza fungi was confirmed by the colonization test (Fig. S1). Results in the form of the significance of two-way ANOVA test output, performed to assess the influence of independent variables like NaCl concentration and AMF inoculation and their interaction on photosynthesis pigments (chlorophyll a, chlorophyll b, total chlorophyll and carotenoids), total soluble sugars (TSS), proline, lipid peroxidation (MDA), H2O2 and antioxidant enzymes (SOD,
Discussion
Chlorophyll content, as a key factor of plant photosynthesis, closely reflects photosynthetic ability of plant (Ruiz-Lozano et al., 2018) and since it is reduced under the salt stress (Abdelhamid et al., 2019; Porcel et al., 2012; Ruiz-Lozano et al., 2018), it was the first parameter to be tested. Results showed that total chlorophyll, chlorophyll a and b levels were higher in AMF inoculated GF677 plants than in control plats at majority of tested NaCl concentrations, which was in particular
Conclusion
The results of this study showed that under salinity stress inoculation of GF677 rootstock with arbuscular mycorrhizal fungi improves many of plant physiological parameters (like chlorophyll, soluble sugars and proline content) and increases activity of antioxidant enzymes. Observed changes as a response to salt stress are usually a part of a physiological profile noticed in saline tolerant genotypes in different plant species, thus our findings suggest that the salinity tolerance of trees from
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
CRediT authorship contribution statement
Roohollah Shahvali: Investigation, Methodology, Formal analysis, Visualization, Writing - original draft. Behrouz Shiran: Conceptualization, Investigation, Supervision, Resources. Rudabeh Ravash: Project administration, Funding acquisition. Hossein Fallahi: Data curation, Validation, Software. Bojana Banović Đeri: Writing - original draft, Writing - review & editing.
Acknowledgments
This research was partially supported by Shahrekord University. We would like to acknowledge the Biotechnology Research Institute of Shahrekord University, which assisted in the realization of this project. We also thank Dr. H. Nourbakhsh for providing GF677 rootstocks.
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