Changes in antioxidant enzymes activities and physiological traits of ajowan in response to water stress and hormonal application

Two separate field experiments (split plot with RCB design) with three replications were undertaken in 2014 and 2015, to evaluate the effects of salicylic acid (SA) (0 and 1 mM) and abscisic acid (ABA) (0 and 50 mu M) on enzymes activities, soluble sugars, anthocyanin content and physiological traits of ajowan (Carum copticum L.) under different irrigation intervals (irrigation after 70, 100, 130 and 160 mm evaporation). Ajowan plants responded to different levels of water limitation by increasing the activities of antioxidant enzymes such as ascorbate peroxidase (APX), catalase (CAT), peroxidase (POX) and polyphenol oxidase (PPO) against free radicals. Soluble sugars and anthocyanin contents and leaf temperature (LT) were also increased, but percentage of ground green cover (PGC), leaf water content (LWC), membrane stability index (MSI), chlorophyll a (Chl a), chlorophyll b (Chl b) and carotenoid content decreased with increasing water stress. All traits were significantly enhanced by SA treatment. Application of ABA significantly increased PGC, LWC and MSI, but had no significant effects on Chl b and carotenoid contents. However, treatment with ABA resulted in reduction of Chl a under severe stress. LT declined as a result of SA and ABA applications. Improving physiological performance and carbohydtate metabolism due to foliar spray of SA and ABA was also a way for ajowan plants to cope with adverse environmental conditions such as water deficit.