Oxidative stress and physiological damage under prolonged heat stress in C3 grass Lolium perenne

Improving tolerance to heat stress is a major challenge in many C-3 crops given the threat of global warming. Populations of perennial ryegrass (Lolium perenne L.) tolerant and sensitive to summer stress in the field were exposed to moderately high temperature stress (36 degrees C) or high temperature stress (40 degrees C). Physiological damage (maximal efficiency of photosystem II, cell membrane stability and lipid peroxidation) and contents of hydrogen peroxide (H2O2) in leaves were monitored during the exposure to stress. The tolerant populations showed significantly lower degree of physiological damage than the sensitive one only at moderate levels of stress (36 degrees C); the tolerant population had significantly lower amounts of H2O2 in leaves. The accumulated H2O2 content showed a linear relationship with the extent of physiological damage. These results suggest that population difference in heat tolerance is associated with tolerance to oxidative stress and the difference in sensitivity is due to accumulation of H2O2 rather than tolerance to H2O2.