Biochemical and Molecular Basis of Varietal Difference in Plant Salt Tolerance

Abstract

World agriculture is facing a lot of challenges like producing 70% more food for an additional 2.3 billion people by 2050. However, the productivity of crops is not increasing in parallel with the food demand. The lower productivity is attributable to various abiotic stresses, of which increased soil salinity is one of the foremost causes. The negative effect of salinity is caused by Na+ and Cl- ions producing the critical conditions for plant survival. The obvious outcome of salinity includes membrane damage, nutrient imbalance, altered levels of growth regulators, enzymatic inhibition and improper metabolic functions, including photosynthesis which ultimately leads to plant demise. Crops vary significantly in their threshold limits of salt tolerance. A well-focused approach combining the molecular, physiological, biochemical and metabolic aspects of salt tolerance is essential to alleviate the drastic effects of salinity and develop salt-tolerant crop varieties. The exploitation of genetic differences of available germplasm has the greatest significance, because it helps to identify the genotypes performing well even under saline conditions. Screening of crops for tolerance can strengthen the breeding programs by identifying genotypes with high salt tolerance and yield potential. This strategy involves comparative investigation of various morphological, physiological, biochemical, enzymatic and ionic responses, together with the study of differential expression pattern of genes/proteins concerned with salt tolerance at different developmental stages under salt stress in salt-sensitive and salt-tolerant cultivars. If the response is greater in the salt-tolerant line, it suggests a role in stress tolerance. Many pitfalls are associated with such approach, i.e., climatic variation, varied physiochemical properties of soil and amount of precipitation, which reduces the effectiveness of screening under field conditions. Even then, such studies can readily identify the salt-tolerant genotype, leading to the identification of novel genes or markers contributing towards salt tolerance, when overexpressed in the susceptible cultivars. The tolerant genotypes, thus screened can be recommended for cultivation in marginal salt-affected areas. This review focuses on the biochemical and molecular basis of varietal differences in salt tolerance among the cultivars of various plant species.