Salicylic acid changes plant growth parameters and proline metabolism in Rauwolfia serpentina leaves grown under salinity stress.

Salicylic acid (SA, 50µM) improved key plant growth parameter, osmolytes (proline, glycinebetaine) accumulation and proline metabolism in leaves of medicinally important Rauwolfia serpentina plants grown under salinity stress (100 mM NaCl). SA induced significantly plant growth in terms of dry weight, water content (%), photosynthetic pigments and protein contents in both saline and non-saline conditions. The proline accumulation and proline synthesis enzymes like, pyrroline-5-carboxylate reductase, -glutamyl kinase were increased significantly in presence of NaCl but highly significant was found in presence of SA under NaCl stress. The proline oxidase activity was inhibited in all treatments than the non-saline control. Therefore, the application of SA under NaCl stress, proline metabolism was significantly altered and the extent of alteration varied between the SA and salt stress, leading to the maintenance of the turgor by accumulating significant higher levels of proline accumulation in R. serpentina, supporting its protection from salinity stress. Further, with addition of SA under salt stress of R. serpentina was evident from the higher level of glycinebetaine (GB) over that of non-saline control or/others treatments. Hence, SA interaction with salt had a cumulative effect on proline metabolism.