Antioxidant Defences under Hyperoxygenic and Hyperosmotic Conditions in Leaves of Two Lines of Maize with Differential Sensitivity to Drought

The effects of hyperoxygenic and hyperosmotic stress on several aspects of antioxidant defences were studied in the leaves of a drought-sensitive (LG11) and a drought-tolerant (LIZA) line of maize (Zea mays L.). When leaf disks were subjected to the severest stress conditions (100% O2 and 0.5 M mannitol), the activities of antioxidant enzymes, such as superoxide dismutase (SOD), catalase (Cat), ascorbate peroxidase (Asc-Px) and glutathione reductase (GSSG-Red), remained higher in disks of LIZA than in disks of LG11. The ratios of activities of SOD to Cat, SOD to Asc-Px and SOD to GSSG-Red were much higher in leaf disks from LG11 than in those from LIZA. Damage, as indicated by, for example, the extend of lipid peroxidation, the destruction of chlorophyll and carotenoids, the decrease in levels of protein sulfhydryl groups and the leakage of electrolytes from cells was apparent in leaf disks of both LIZA and LG11 as consequence of the applied stresses. However, the damage was less marked in LIZA than in LG11.