Effects of water deficit on growth and proline metabolism in Sesuvium portulacastrum

Response to water deficit was studied in Sesuvium portulacastrum, a promising halophyte for saline soil stabilisation and covering. After their multiplication and ample irrigation, seedlings were cultivated for 4 weeks under optimal or limiting water supply (respectively, 100 and 25% of field capacity, FC). A subset of stressed plants was thereafter subjected to the optimal regime of irrigation. Weekly harvests were carried out during 70 days of treatment. Measured parameters were growth, tissue water and proline contents, as well as ornithine-δ-aminotransferase (δ-OAT, EC 2.6.1.13) and proline dehydrogenase (PDH, EC 1.5.1.2) activities. Water deficit reduced the growth (whole plant biomass and leaf number), increased root/shoot ratio and led to a significant decrease in leaf relative water content (RWC). In water-stressed plants, the concentration of K+, Na+, Cl− and proline, as well as δ-OAT activity increased significantly. Inversely, PDH activity was impaired. Rewatering stressed plants restored these parameters at values close to those of plants permanently irrigated with 100% FC.It can be assumed that ornithine pathway contributed via an increase in δ-OAT activity to proline synthesis in water-stressed plants of S. portulacastrum at the adult stage. Results suggest also that S. portulacastrum conserved its growth potentialities and nutrient acquisition systems during long-term water deficit stress, as shown by the re-establishment of the growth activity and leaf development, following relief of stress.