Photosynthesis, Membrane Stability and Proline Metabolism Enzyme Activity as Potential Indicators for Salt Tolerance in Wheat

An experiment was conducted to study the impact of differential physiological and biochemical indicators on salinity tolerance in wheat. Wheat cultivars Raj-3777 (salinity tolerant) and HD-2687 (salinity susceptible but widely cultivable) were grown in ceramic pots and filled with 15 kg soil mixed with recommended doses of manures and fertilizers. Seeds were sown in normal water and saline water was applied after the plant establishment. Saline water of electrical conductivity (EC) 0 (tap water), 4, 8 and 12 dSm(-1) were prepared by mixing chloride and sodium salts in 3 : 1 ratio using NaCl, Na2SO4, CaCl2 and MgCl2 and applied to plants as and when required to maintain the desired level of salinity. The result showed that the tolerant cultivar Raj-3777 exhibited a different pattern of responses compared to HD-2687 for most of the recorded parameters. Inhibition in photosynthetic rate, transpiration rate and stomatal conductance were lesser in Raj-3777 compared to HD-2687. The chlorophyll content, relative water content, cell membrane stability and protein content were higher in the leaves of tolerant cultivar under saline conditions. It exhibited higher sodium accumulation in root via managing restricted translocation of sodium on the cost of potassium. Thus, the potassium content was recorded higher in leaves than roots. The inhibition of pyrroline-5-carboxylate synthetase (P5CS), pyrroline-5-carboxylate reductase (P5CR), ornithine-delta-aminotransferase (OAT) and proline dehydrogenase (ProDH) activities were recorded higher in the tolerant cultivar. The study envisaged that the lesser reduction in net photosynthetic rate, lower electrolyte leakage, maintenance of higher leaf water status, retention of chlorophyll and high potassium content in leaves on the cost of low sodium transportation from roots might be the potential indicators for selection of salt-tolerant wheat cultivars, which can be used for its improvement through transgenic approaches. The observed negative relationship between the amount of proline accumulation and the level of salt tolerance did not support the widely advocated role of proline as an osmoprotectant under salt stress.