Enzymatic Antioxidant Responses of Local and Improved Drought Tolerant Varieties of Maize (zea Mays L) to Water Stress

ABSTRACT Water stress is one of the major forms of abiotic stress factors that adversely affect the growth and yield of maize crops, especially in arid and semi-arid regions. Sustainable maize production under changing climatic conditions, especially water stress conditions, is one of the key challenges that need to be addressed. This study evaluated the impact of different levels of water stress on antioxidant enzyme activities of ascorbate peroxidase (APX), guaiacol peroxidase (GPX) and glutathione reductase GR) at vegetative stage in local (TZM 154, TZM 1389, TZM 1414 and TZM 1136) and an improved drought tolerant (SAMMAZ 45) varieties of maize using standard methods. Three stress treatments; T1 (100% WFC), T2 (50% WFC) and T3 (25% WFC) representing unstressed, moderately stressed and severely stressed conditions respectively were administered for four weeks after two weeks of growth establishment. Enzyme assays were conducted spectrophotometrically on the leaf samples. Generally, the antioxidant enzyme activity was observed to increase significantly (p˂0.05) as water stress treatment was intensified in all maize varieties with the highest antioxidant activity recorded in the improved drought tolerant variety (SAMMAZ 45) (54.57±0.15 and 80.24±0.04) for ascorbate peroxidase and glutathione reductase. However, among the local varieties, TZM 1414 and TZM 154 showed high antioxidant responses, particularly in terms of guaiacol peroxidase (GPX) activity (7.27±0.02 and 7.58±0.07 respectively) compared to the improved variety. Under severe stress treatment (T= 25%WFC), TZM 1414 showed a close level of ascorbate peroxidase activity as the improved variety (SAMMAZ 45). TZM 1414 and TZM 154 express close levels of glutathione reductase activity compared to the improved variety (SAMMAZ 45). This suggests these varieties have promising antioxidant potential which could be exploited for genetic improvement of maize genotype that are resilient to drought stress.