Proline Metabolism Under Water Stress in the Leaves and Roots of Brassica juncea Cultivars Differing in Drought Tolerance

Plant water relations, proline content and activities of pyrroline-5-carboxylate synthetase (P5CS) and proline oxidase (PO) were studied in five Brassica juncea genotypes differing in drought response. Under water stress, drought tolerant cv Varuna showed maximum osmotic adjustment value (1/b) of 3.21. In this variety, proline content increased from 8.4 and 5.3 μmol g−1 dry weight under normal conditions to 128.2 and 44.5 μmol g−1 dry weight under stress conditions in the leaves and roots respectively. The increase in proline content in less drought tolerant variety Prakash was from 7.0 and 1.8 μmol g−1 dry weight In the absence of stress to 62.9 and 13.4 μmol g−1 dry weight in the presence of stress in leaves and roots respectively. Compared to the respective controls, increase in the activity of proline biosynthetic enzyme P5CS of roots and leaves under water stress was maximum (∼ 94%) in Varuna and minimum in Prakash (∼16%). Reduction in the activity of proline degrading enzyme PO due to stress was also maximum in the leaves (75%) and roots (87%) of Varuna. These results showed genotype dependent effect of water stress on plant water relations and proline metabolism.