Effect of salicylic acid on photochemistry and antioxidant capacity in Salvia nemorosa plants subjected to water stress

Oxidative stress is commonly induced when plants are grown under drought stress conditions.To analyze how salicylic acid (SA) can partly alleviate drought-induced oxidative stress and negative impacts of drought on physiology and growth of Salvia nemorosa plants, we investigated the physiological responses of S. nemorosa to SA application under drought stress. The treatments were composed of Co (control, 100% field capacity), Dr (drought, 50% field capacity), SA (500 µM) and DSA (SA drought). Plant growth and relative water content (RWC) were negatively affected by drought stress; however, SA treatment significantly improved the growth rate and enhanced the drought tolerance of seedlings. This increased tolerance in SA-supplied plants was obtained by reduced damaging effect on performance index (PIabs) and maximal quantum yield of photosystem II (PSII) (Fv/Fm) through improvement of reaction centers (RC/CS) with associated changes in excitation energy trapping (TRo/CS) and electron transport (ET0/CS) per excited cross-section of leaf. Additionally, under drought condition, plants cultivated with SA exhibited better protection against oxidative damage because of higher catalase (CAT) and ascorbate peroxidase (APX) activities and lower levels of malondoialdehyde (MDA) and hydrogen peroxide (H2O2). The present study suggests that salicylic acid can play a protective role during drought stress by enhancing the photosynthetic capacity and the antioxidant defense system.