Changes in antioxidant enzymes activities and alkaloid amount of Catharanthus roseus in response to plant growth regulators under drought condition

• Drought stress improved production of vinblastine and vincristine contents in Catharanthus roseus . • Salicylic acid improved the vinblastine and vincristine contents in drought and good irrigation conditions. • Jasmonic acid reduced the improvement impact of salicylic acid on the pigments under good irrigation and moderate drought. • Salicylic acid low concentrations and jasmonic acid had a synergistic positive effect on total fresh and dry weights. • Drought stress increased the plant antioxidant activity in Catharanthus roseus. Drought stress affects plant growth and is considered as one of the most important issues in In Middle East. In order to manage the critical water, it is essential to develop strategies to improve plant growth and biochemical characteristics. Plant growth regulators may afford a safe solution to increasing crop productivity via several mechanisms. Thus, the current study investigated the influence of salicylic acid and jasmonic acid on some physiological and antioxidant responses of Catharanthus roseus to drought stress under field conditions in Ahvaz and Tehran, Iran. The results indicated drought stress decreased total fresh and dry weights, relative water content, and concentration of photosynthetic pigments. In contrast, the activity of antioxidant enzymes and alkaloid contents would be increased. Foliar application of salicylic acid had a significant impact on all studied traits, but jasmonic acid had an effect only on total fresh and dry weights, concentration of photosynthetic pigments, and alkaloid contents. The activity of antioxidant enzymes including peroxidase, ascorbate peroxidase, superoxide dismutase, and polyphenol oxidase enhanced by spraying salicylic acid in deficit and good irrigation conditions. Foliar application of salicylic acid 10 mM on activity of antioxidant enzymes and salicylic acid 1 mM on relative water content and photosynthetic pigment content were more effective than other salicylic acid concentrations. Foliar application of jasmonic acid increased total fresh and dry weights also carotenoid content, but decreased total chlorophyll contents under stress conditions, in both places. Application of salicylic acid 0.1 mM + jasmonic acid increased total fresh and dry weights in any irrigation regimes, while this treatment increased carotenoid contents only under drought conditions in Ahvaz. Application of salicylic acid alone and with jasmonic acid significantly increased the alkaloid contents under severe drought stress. Salicylic acid improved C. roseus physiological performance and alkaloid contents, also it could be a way for periwinkle to alleviate the adverse effects of drought stress.