Heat stress injury in relation to membrane lipid peroxidation in creeping bentgrass

Understanding physiological and biochemical factors involved in heat-stress injury would help improve heat tolerance of cool-season grasses. The objective of this study was to investigate lipid peroxidation of cell membranes in relation to heat-stress tolerance in creeping bentgrass (Agrostis palustris Huds.). Two creeping bentgrass cultivars differing in heat tolerance, L-93 (heat tolerant) and Penncross (heat sensitive) were grown under two temperature regimes: 22/16 degrees C (day/night) and 35/25 degrees C for 56 d in growth chambers. Photochemical efficiency (Fv/Fm) and chlorophyll content of leaves; and electrolyte leakage (EL); content of the lipid peroxidation product, malondialdehyde (MDA); and activities of antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) in leaves and roots were determined biweekly during heat stress. Leaf Fv/Fm ratio and chlorophyll content decreased, whereas EL and MDA contents of both leaves and roots increased under heat stress in both cultivars, but to a greater extent in Penncross. The activities of SOD and CAT decreased, whereas POD activity increased in both leaves and roots, which occurred to a greater extent for Penncross. The increases in MDA content and POD activity under heat stress were greater for leaves than for roots in both cultivars. These results suggest that decreased activities of antioxidant enzymes could result in an increased level of lipid peroxidation. Thus, decreased activities of antioxidant enzymes could contribute to damage of cell membranes and to leaf senescence as demonstrated by increased EL and reduced Fv/Fm, and by decreased chlorophyll content during heat stress. Cultivar variations in antioxidant enzyme activities were associated with their differences in heat tolerance as evidenced by Fv/Fm ratio, chlorophyll content, and EL.