Physiological Modifications and Enzymatic Defense System of Amaranthus blitoides S. Watson and Amaranthus hybridus L. in Response to Water Deficit Stress

Amaranthus blitoides S. Watson and A. hybridus L. competes with summer crops and reduces their growth and yield. Drought stress as an environmental limiting factor can impair plant growth. The goal of the study was to investigate the effect of drought stress (no drought stress, light, moderate, high, and severe drought stress) on physiological characteristics and enzymatic defense system of A. blitoides and A. hybridus in two separate experiments. Drought stress reduced plant chlorophylls a and b content of A. blitoides and A. hybridus . Carotenoid content of both A. blitoides and A. hybridus decreased in response to the drought stress and reached to the maximum in severe drought stress condition. Drought stress increased the content of the activity of catalase (CAT), and superoxide dismutase (SOD), and proline in both years. The highest level of CAT (102.9 units/mg protein) and SOD activity (2333.3 units/mg protein) was observed in 2019 in response to severe stress. Drought stress decreased the soluble protein content of the plant. In the second year of the experiment, CAT, SOD, proline, and carotenoid showed a further enhancement compared to the first year because of higher temperature in the second year of the experiment. The results of the research showed that A. blitoides and A. hybridus can tolerate prolonged drought stress and survive by modification in biochemical activity and activation of the enzymatic defense system.