The antioxidant defense and glyoxalase systems contribute to the thermotolerance of

This study focused on the impact of the antioxidant defence and glyoxalase systems on extreme heat tolerance of the thermophilic plant Heliotropium thermophilum L. For this purpose, plants were exposed to 20, 40, 60 and 80 ± 5°C soil temperature gradually for 15 days under laboratory conditions. Our results showed that the hydrogen peroxide and superoxide levels of H. thermophilum were lower at 40 ± 5°C and higher at 80 ± 5°C compared with plants grown at 20 ± 5°C. Some antioxidant enzyme activities tended to increase in plants at 40, 60 and 80 ± 5°C compared with those at 20 ± 5°C and the protein contents responsible for the antioxidant enzymes were in parallel with these enzyme activities. The contents of both reduced and oxidised ascorbate and glutathione rose with increasing temperature. Methylglyoxal level was lower at 40 ± 5°C and higher at 80 ± 5°C compared with plants grown at 20 ± 5°C. Glyoxalase activities highly increased with rising of soil temperature from 20 ± 5°C to 80 ± 5°C. The results of this study suggest that differential modulations of enzymatic antioxidants and the increase in non-enzymatic antioxidants and glyoxalase activities can contribute to the development of the thermotolerance of H. thermophilum through the detoxification of reactive oxygen species and methylglyoxal.