Heat tolerance and suppression of oxidative stress: Comparative analysis of 25 cultivars of the C3 grass Lolium perenne

Plants exposed to high temperatures frequently suffer from oxidative stress. A large difference was observed among cultivars of Lolium perenne L. in the extent to which their growth in field had been damaged during summer. This study seeks to clarify the relationships between the heat tolerance and tolerance to oxidative stress among the cultivars in this species. Twenty-five cultivars of L. perenne with different degrees of field tolerance to high summer temperatures were exposed to moderately high temperatures (36/30 °C) for 40 days in a growth chamber. The field tolerance showed a negative correlation with H2O2 content (r = −0.66**) and with the degree of lipid peroxidation (r = −0.65**) in leaves after 40 days of exposure to stress, which suggest involvement of oxidative stress in the field tolerance. The H2O2 content was positively correlated with electron transport rate (r = 0.56**) and negatively correlated with leaf thickness (r = −0.63**). Tetraploid cultivars, because of their thicker leaves, had higher field tolerance and lower H2O2 content than diploid cultivars. These results suggest that the balance between electron transport and CO2 reduction in photosynthetic response, which is largely influenced by leaf thickness, plays a pivotal role in determining H2O2 generation and resulting oxidative damage under prolonged exposure to moderate to high temperatures.

► Twenty-five cultivars of L. perenne with different degrees of field summer tolerance were examined in relation to tolerance to oxidative stress.
► All cultivars were exposed to 36/30 °C for 40 days in a growth chamber.
► Cultivars with low field tolerance had higher H2O2 content and higher degree of lipid peroxidation than those with high tolerance.
► The results showed that both H2O2 production and H2O2 scavenging contribute to cultivar differences in heat tolerance.