Salt-induced changes in photosynthetic activity and oxidative defense system of three cultivars of mustard (Brassica juncea L.)

Abstract

A greenhouse experiment was conducted to assess salt-induced modulation in gas exchange attributes and some key enzymes of oxidative defense system in three cultivars of mustard (Brassica juncea L.), Varuna, RH-30 and Rohini, under saline conditions. After 21 days of seed germination, three salt treatments (0, 100 and 200 mM NaCl) were applied to the root growing medium. Salt treatments for three weeks significantly decreased the biomass, shoot and root lengths, CO2-assimilation rate (A), transpiration rate (E), stomatal conductance (gs), chlorophyll a and b pigments and relative water contents (RWC), while electrolyte leakage, proline, H2O2,malondialdehyde (MDA) and activities of superoxide dismutase (SOD), peroxidise (POD), catalase (CAT) and glutathione reductase (GR) enzymes increased in all three mustard cultivars. In comparison with the two other cultivars, cv. Varuna had higher shoot fresh and dry weight, proline content and activities of SOD, ascorbate peroxidase (APX), CAT and GR, while RH-30 and Rohini were higher in electrolyte leakage, H2O2 and MDA levels. Overall, the differential growth of all three mustard cultivars under saline conditions was found to be attributable to differential photosynthetic and transpiration rates, stomatal conductance, chlorophyll pigments and relative water contents, hence these could be used as potential selection criteria for screening mustard germplasm for salt tolerance. Key words: Salt stress, Brassica juncea, antioxidant enzymes, proline.