RESPONSE OF MAIZE TO FIELD DROUGHT STRESS: OXIDATIVE DEFENSE SYSTEM, OSMOLYTES' ACCUMULATION AND PHOTOSYNTHETIC PIGMENTS

The study was performed to determine as to whether antioxidant potential (enzymatic and non-enzymatic antioxidants) as well as some other attributes could be used as potential drought resistance markers in two maize lines (B-73 and MO17). Under water deficit conditions, growth traits, relative water content (RWC), chlorophyll a, total chlorophyll and carotenoids as well as grain yield decreased significantly in both lines compared to those under control conditions. In contrast, water deficit caused a significant increase in the activities of superoxide dismutase (SOD) and catalase (CAT) isozymes as well as levels of glycine betaine (GB), proline and malondialdehyde (MDA), whereas total phenolics, total soluble protein, H2O2, chlorophyll b, chlorophyll a/b ratio, anthocyanin and peroxidase (POX) isozyme activity remained unaffected in both maize lines. Although water deficit stress induced oxidative stress in both maize lines, the enzymatic and non-enzymatic antioxidants and key organic osmolytes increased significantly in both maize lines. For example, SOD isozyme activities, and GB and proline contents were considerably greater in relatively drought resistant MO17 than those in relatively drought sensitive B-73. However, in contrast, CAT activity was higher in B-73. Overall, SOD isozyme activities, and GB and proline contents were found to be potential biochemical indicators of drought resistance in the two maize lines used in the present study.