Arbuscular mycorrhizal fungi and tolerance of salt stress in plants

Abstract

Soil salinity has become a serious land degradation problem and is increasing steadily in many parts of the world, particularly in arid and semiarid areas. Increased salinization of arable land is expected to have devastating global effects and would lead to 30% land loss within the next 25 years and up to 50% by the middle of the twenty-first century. Plants growing in saline conditions generally last to three distinct stresses, ionic, osmotic, and oxidative. The toxic effects of specific ions such as Na+ and Cl-, prevalent in saline soils, disrupt the structure of enzymes and other macromolecules, damage cell organelles, disrupt general metabolic activities, inhibit protein synthesis, and induce ion deficiency. Plants exposed to low water potential face the problem of physiological drought condition. Moreover, salinity creates nutrient imbalance in the plant due to decreased and differential uptake of nutrients and/or their translocation to the shoot and leaf tissues, rendering the plants weak and unproductive. Arbuscular mycorrhizal fungi (AMF) are ubiquitous soil microorganisms that build up symbiotic associations with the majority of higher plants, establish a direct physical link between soil and plant roots, constitute an integral component of the natural ecosystems, and predominantly exist in the saline environment. The extraradical hyphae of AMF run several meters away from the depletion zone, increase root surface area and facilitate nutrient absorption by the plant. Indeed, AMF improve physiological processes and general metabolic activities of the plant and help in the mitigation of physiological drought, which is often imposed under saline conditions. Therefore, the application of AMF could offer a cheaper and cost-effective alternative to counteract the problem of salinity. In this review chapter, we have discussed the factors influencing soil salinization and possible approaches to overcome the problem of salinity stress. The underlying physiological, biochemical and molecular mechanisms by which mycorrhizal plants could improve salt tolerance has also been described.