Abstract
Modern agriculture is facing twin challenge of ensuring global food security and executing it in a sustainable manner. However, the rapidly expanding salinity stress in cultivable areas poses a major peril to crop yield. Among various biotechnological techniques being used to reduce the negative effects of salinity, the use of arbuscular mycorrhizal fungi (AMF) is considered to be an efficient approach for bio-amelioration of salinity stress. AMF deploy an array of biochemical and physiological mechanisms that act in a concerted manner to provide more salinity tolerance to the host plant. Some of the well-known mechanisms include improved nutrient uptake and maintenance of ionic homeostasis, superior water use efficiency and osmoprotection, enhanced photosynthetic efficiency, preservation of cell ultrastructure, and reinforced antioxidant metabolism. Molecular studies in past one decade have further elucidated the processes involved in amelioration of salt stress in mycorrhizal plants. The participating AMF induce expression of genes involved in Na+ extrusion to the soil solution, K+ acquisition (by phloem loading and unloading) and release into the xylem, therefore maintaining favorable Na+:K+ ratio. Colonization by AMF differentially affects expression of plasma membrane and tonoplast aquaporins (PIPs and TIPs), which consequently improves water status of the plant. Formation of AM (arbuscular mycorrhiza) surges the capacity of plant to mend photosystem-II (PSII) and boosts quantum efficiency of PSII under salt stress conditions by mounting the transcript levels of chloroplast genes encoding antenna proteins involved in transfer of excitation energy. Furthermore, AM-induced interplay of phytohormones, including strigolactones, abscisic acid, gibberellic acid, salicylic acid, and jasmonic acid have also been associated with the salt tolerance mechanism. This review comprehensively covers major research advances on physiological, biochemical, and molecular mechanisms implicated in AM-induced salt stress tolerance in plants. The review identifies the challenges involved in the application of AM in alleviation of salt stress in plants in order to improve crop productivity.
Highlights
Worldwide, soil salinity is becoming a significant problem as it is encountered in all climates
The ability of plants to tolerate salinity stress is usually evaluated in terms of biomass produced
M plants showed higher concentration of these micronutrients than NM plants (Table 1). This may be credited to – (i) widespread root-hyphal system that shortens the path of nutrients’ entry into plant (Subramanian et al, 2009); (ii) fungal mycelium serving as a substrate for nutrients to bind; (iii) arbuscular mycorrhizal fungi (AMF)-induced changes in the pH of the rhizosphere, which modulates nutrient solubility and their availability (Li and Christie, 2001); (iv) increase in sink size of Cu and Zn due to higher shoot P, which subsequently instigate nutrient uptake and translocation to shoots (Liu et al, 2000); (v) up regulation of the expression of transporter gene of these nutrients, for example, a plasma membrane Zn transporter gene, MtZIP2 is up regulated upon colonization by AMF (Burleigh et al, 2003)
Summary
Soil salinity is becoming a significant problem as it is encountered in all climates. Formation of AM has been reported to – (i) improve nutrient acquisition and maintain ionic homeostasis; (ii) improve water uptake and maintain osmotic equilibrium in plants; (iii) induce antioxidant system to prevent damage by ROS; (iv) protect photosynthetic apparatus and enhance photosynthetic efficiency; and (v) modulate phytohormone profile to minimize salt effects on growth and development (Figure 1) (Evelin et al, 2009, 2012; Ruiz-Lozano et al, 2012; Augé et al, 2014; Khalloufi et al, 2017) These effects act in coordination to improve plant’s resilience to salinity stress. It identifies the gaps in the understanding of the mechanisms, and presents the research challenges to be met in the future studies
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
