Morpho-physiological, Biochemical, and Transcript Analysis Revealed Differential Behavior of Chickpea Genotypes Towards Salinity.

Abstract

Till now, limited information was available on salt tolerance chickpea genotypes. Therefore, in comparison to CSG 8962 (check for salinity tolerance), an experiment on nine chickpea genotypes with different background (BG 1103, DCP 92-3, S7, ICCV 10, BG 256, KWR 108, JG 16, K 850, and ICC 4463) was conducted under medium salt stress of EC_iw ~ 6 dS m^-1 and high salt stress of 9 dS m^-1 to evaluate their salt tolerance potential. Different morphological, physiological, biochemical, and molecular traits were studied to characterize these genotypes. It was also noted that growth of all the genotypes was affected by salinity, but more reduction was shown by the genotypes BG 256, DCP 92-3, and ICC 4463. Irrigation water loaded with salts disrupted the water relations as displayed by the reducing values of RWC, water potential, and osmotic potential. Chlorophyll content, when compared with control, reduced in the range of 7.06 to 28.93% at moderate salinity level (EC_iw ~ 6 dS m^-1) and 23.71 to 55.83% at higher salinity level (EC_iw ~ 9 dS m^-1). S7, ICCV 10, KWR 108, and CSG 8962 (salt-tolerant check) maintained optimum gas exchange traits, i.e., photosynthetic rate, stomatal conductance, and transpiration rate with increasing salinity and osmoregulatory compounds, imino acid proline, and total soluble sugars were also higher in these genotypes. Na⁺/K⁺ ratio at control was 0.084 and it enhanced with increasing salinity and noted mean genotypic values of 0.399 and 0.758 at moderate and higher salinity levels, respectively. Antioxidative defense mechanism was quite active in the genotypes (S7, ICCV 10, KWR 108, and check CSG 8962) because higher values of antioxidative enzymes and low increment in the content of hydrogen peroxide and malondialdehyde were noted in these genotypes. Based on the results, genotypes with salinity contrasting response (KWR 108 as tolerant and ICC 4463 as sensitive) were selected, and gene expression studies were conducted along with CSG 8962 (the check). It was found that KWR 108 showed higher expression of Δ1-pyrroline-5-carboxylate synthetase (P5CS), pyrroline-5-carboxylate reductase (P5CR), Na⁺/H⁺ antiporter (NHX1), and sodium transporter HKT1 and downregulation of proline dehydrogenase gene than the genotype CSG 8962 (salt-tolerant check). So, it was concluded that genotypes, i.e., S7, KWR 108, and ICCV 10, maintained higher physiological and biochemical efficiency in terms of lower ψ_w, ψ_s, and membrane stability, higher RWC, photosynthetic rate, and osmolyte accumulation as well as antioxidative enzyme activities in comparison to the salt-tolerant check used in the study. Further, these results were validated through gene expression studies which revealed similar results that categorized these genotypes to be salt tolerant.