Comparative response of maize and rice genotypes to heat stress: status of oxidative stress and antioxidants

In the present study, two genotypes each of maize and rice were compared for their response to varying degrees of temperature stress (35/30, 40/35, 45/40A degrees C) with controls growing at 30/25A degrees C. At elevated temperatures of 40/35 and 45/40A degrees C, the rice genotypes were inhibited to a significantly higher extent, especially for their shoot growth compared to maize genotypes. The stress injury measured as damage to membranes, loss of chlorophyll and reduction in leaf water status was significantly higher in rice plants, especially at 45/40A degrees C. The components of oxidative stress particularly the level of malondialdehyde was significantly greater in rice plants while the differences for hydrogen peroxide concentrations were small at 40/35 and 45/40A degrees C. The expression of enzymatic antioxidants like catalase, ascorbate peroxidase and glutathione reductase was found to be higher in maize plants compared to rice plants while no variations existed for superoxide dismutase at 45/40A degrees C. In addition, the non-enzymatic antioxidants like ascorbic acid, glutathione and proline were maintained at significantly greater levels at 45/40A degrees C in maize than in rice genotypes. These findings suggested that maize genotypes were able to retain their growth under high-temperature conditions partly due to their superior ability to cope up with oxidative damage by heat stress compared to rice genotypes. Since, maize and rice belong to C-4 and C-3 plant groups, respectively, these observations may also reflect the relative sensitivity of these plant groups to heat stress.