Epichloe endophyte infection improved drought and heat tolerance of tall fescue through altered antioxidant enzyme activity

Background of the study; Epichloe species are fungal endophytes of many cool season grass species. The Epichloe-tall fescue association is generally known to confer drought tolerance of tall fescue although the effect varied depending a lot of factors. Besides, few studies are focused on the effect of fungal endophyte on heat tolerance of tall fescue. Objectives: This study was to investigate the effect of fungal endophyte on drought and heat tolerance of tall fescue. Methods: In this study, endophyte infected (E+) and non-infected (E-) tall fescue plants were exposed to two separate experiments, drought tolerance experiment and heat tolerance experiment. Physiological parameters and antioxidant enzyme activity were measured. Results: Compared with E- plants, lower levels of electrolyte leakage, malondialdehyde content, and hydrogen peroxide (H2O2) content were observed in E+ plants during drought, re-watering and heat stress treatment. Lower level of superoxide (O-2-) content was also observed in E+ plants upon re-watering. In addition, endophyte infection promoted higher relative water content and higher superoxide dismutase (SOD) and ascorbate peroxidase (APX) activity at the end of drought treatment. E+ plants had higher levels of catalase (CAT), guaiacol peroxidase (POD) and APX activity than E- plants by the end of heat treatment. Conclusions: Our results support a protective role of the endophyte in conferring drought and heat tolerance of tall fescue. E+ plants appear to reduce ROS (reactive oxygen species, e.g., O-2- and H2O2) production in part by maintaining higher enzyme activity of SOD and APX under drought and CAT, POD and APX activity under heat stressed conditions.