Improvement in drought stress tolerance of safflower during vegetative growth by exogenous application of salicylic acid and sodium nitroprusside

Drought is a major abiotic stress limiting the agricultural production of safflower (Cardicanus tinctorius L.). To mitigate stress, the effects of salicylic acid and sodium nitroprusside on the growth of Carthamus tinctorius L. under normal and water deficit conditions were studied to understand the underlying stress tolerance mechanisms. Nitric oxide is an important signaling molecule in the regulation of diverse physiological processes specially stress tolerance. Salicylic acid is a growth regulator playing important roles in mitigating both biotic and abiotic stresses. The plants aged 23-days old were irrigated with different field capacity volumes of water (25% and 100%) with or without salicylic acid (0 and 250 mu M) and sodium nitroprusside (0 and 25 mu M). The plants were harvested and characterized by spectrophotometer and gel electrophoresis for certain physiological and biochemical features. The salicylic acid caused rapid activation of non-enzymatic defense system accompanied by increased production of osmolytes and such non-enzymatic scavengers as proline. The sodium nitroprusside application was more activated the enzymatic defense system, promoted the superoxide dismutase and catalase activities and gene expression of two subunits of Fe- and Cu-superoxide dismutase. Both of these adaptive mechanisms reduced free radicals as well as lipid peroxidation and improved the membrane stability and water deficit tolerance of the plants. Their combined applications brought the plant to nearly normal growth conditions. The simultaneous or separate application to plants under normal growth conditions are not suggested as they will act as stress and impair plant growth.