Proline and Proline Metabolising Enzymes in in-vitro Selected NaCl-tolerant Brassica juncea L. under Salt Stress

Abstract The effect of salt stress was studied on proline accumulation and the activities of proline metabolic pathway enzymes in seedling and leaf tissue of two genetically stable lines (SR2P1-2 and SR3P6-2) of in vitro selected NaCl-tolerant plants and parent cultivar Prakash of Brassica juncea L. Salt stress caused differential enhancement in proline level in both seedlings and leaf tissue of plants at different developmental stages. The magnitude of increase in proline content was higher in SR3P6-2 line in seedlings (34 fold at 140 meq -1 NaCl) as well as leaves (16 fold at 40 d after sowing at 100 meq -1 NaCl) compared to the parent cv. Prakash (29 fold in seedlings and five fold in leaves) and SR2P1-2 (21 fold in seedlings and five fold in leaves) at similar stress levels. Salt stress also resulted in changes in the activities of enzymes of proline metabolism. The activities of proline biosynthetic enzymes, pyrroline-5-carboxylate reductase and ornithine aminotransferase, increased under salt stress both in the seedlings and leaves. The range of increase in the activities of the two enzymes was relatively higher in SR3P6-2 (3·3-3·9 fold) compared to the SR2P1-2 (1·8-2·8 fold) and parent cv. Prakash (1·5-2·8 fold). The activity of proline degrading enzyme, proline oxidase, decreased under salt stress in both the tissues of all the lines; the reduction in activity was relatively greater in SR3P6-2 compared to SR2P1-2 or cv. Prakash. The trend of changes in the enzyme activities was in tune with the increase in proline level, the magnitude of change did not match the extent of increase in proline level.