Modulation of defence responses by improving photosynthetic activity, antioxidative metabolism, and vincristine and vinblastine accumulation in Catharanthus roseus (L.) G. Don through salicylic acid under water stress

A pot experiment was conducted to find out whether the foliar spray of salicylic acid (SA) could successfully ameliorate the adverse effects of water stress on periwinkle. Pots were irrigated with ground water regularly as a control and other treatments were given as 15 and 30 days interval drought (DID) at 30 DAS. Plants were uprooted randomly at 46 and 61 DAS, washed carefully and separated into root, stem and leaf for analyses. A uniform concentration (10−5 mol/l) of salicylic acid (SA) was applied as a foliar spray at the vegetative stage. Water stress significantly reduced the growth attributes including plant height, leaf-area index, shoot and root fresh weights, shoot and root dry weights. Long term water stress led to a gradual decrease in photosynthetic parameters and activities of nitrate reductase and carbonic anhydrase. Ascorbic acid, total alkaloids and antioxidant enzymes: superoxide dismutase, catalase and peroxidase increased in stress faced plants. Foliar application of SA (10−5 M) reduced the damaging effect of stress on plant growth and accelerated the restoration of growth processes. It not only improved the growth parameters but also partially reversed the effects of salinity. Total alkaloid content was improved by SA application both in unstressed and stressed plants. Foliar spray of SA not only overcame the adverse effect of stress but also improved the content of vincristine and vinblastine in stressed plants.