Salicylic acid restrains nickel toxicity, improves antioxidant defence system and enhances the production of anticancer alkaloids in Catharanthus roseus (L.).

Salicylic acid (SA) has been reported to ameliorate various stresses in plants. In order to explore the role of SA under nickel (Ni) stress, thirty-days old plants of periwinkle (Catharanthus roseus L.) were supplied with eight treatments comprising basal application of Ni (0, 50, 100 and 150 mg kg(-1)) and foliar application of SA (0 and 10(-5)M) under net house conditions. Ni application significantly reduced the growth attributes including plant height, leaf-area index and fresh and dry weights of shoot and root. Increasing Ni concentration led to a gradual decrease in photosynthetic parameters and activities of nitrate reductase and carbonic anhydrase. The plants, undergoing Ni stress, exhibited a significant increase in the activity of superoxide dismutase, catalase and peroxidase together with an increase in electrolyte leakage and proline content. Total alkaloid content was also declined in Ni-treated plants. Foliar application of SA (10(-5)M) reduced the deleterious effects of Ni on plant growth, accelerating the restoration of growth processes. SA also improved the total alkaloid content under normal as well as adverse conditions. Foliar spray of SA significantly improved the content of anticancer alkaloids vincristine (by 22.2%) and vinblastine (by 50.0%) in plants treated with 150 mg kg(-1) of Ni.