Plant growth, ion accumulation, and antioxidant enzymes of endophyte-infected and endophyte-free tall fescue to salinity stress

Endophyte-mediated salinity tolerance is largely unknown in tall fescue [Schedonorus arundinaceus (Schreb.)]. The experiment was designed to characterize growth, ion accumulation, and antioxidant metabolism of tall fescue infected by the endophyte Epichloe coenophiala to different levels of salinity stress. Endophyte-infected (E+) and endophyte-free (E-) tall fescue (cv Kentucky 31) plants were exposed to 10 d of 0 (unstressed control), 100 and 200 mM NaCl treatments in a greenhouse, respectively. Salinity stress caused reductions in plant height, leaf fresh weight (LFW), leaf dry weight (LDW), and leaf water content (LWC), and increased Na+ concentration, but E + plants had significantly higher LFW, LDW, and LWC under both NaCl treatments and lower Na+ than E- plants under 200 mM NaCl. Salinity stress decreased K+ and Mg2+ and did not alter P, and increased Ca2+ in E + plants and caused no change in Ca2+ in E- plants; however, endophyte had no effects on these elements. Chlorophyll fluorescence (Fv/Fm), malondialdehyde (MDA) concentration, and activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) remained unchanged in E + plants, but Fv/Fm was reduced and MDA level and enzyme activities were elevated in E- plants under 200 mM NaCl, where E + plants had significantly higher Fv/Fm and lower MDA, SOD, and APX activities than E- plants. Peroxidase activities increased in E + plants under 200 mM NaCl and in E- plants under both NaCl treatments. The results indicated that endophyte promoted salinity tolerance in tall fescue through maintaining higher growth and photochemical efficiency and lowering Na+ accumulation and lipid peroxidation. The significantly induced antioxidant enzyme activities and lipid peroxidation in E- plants suggested a possible enhanced oxidative injury in endophyte-free plants exposed to a high level of salinity stress.