Abstract
Drought stress decreases crop growth, yield, and can further exacerbate pre-harvest aflatoxin contamination. Tolerance and adaptation to drought stress is an important trait of agricultural crops like maize. However, maize genotypes with contrasting drought tolerances have been shown to possess both common and genotype-specific adaptations to cope with drought stress. In this research, the physiological and metabolic response patterns in the leaves of maize seedlings subjected to drought stress were investigated using six maize genotypes including: A638, B73, Grace-E5, Lo964, Lo1016, and Va35. During drought treatments, drought-sensitive maize seedlings displayed more severe symptoms such as chlorosis and wilting, exhibited significant decreases in photosynthetic parameters, and accumulated significantly more reactive oxygen species (ROS) and reactive nitrogen species (RNS) than tolerant genotypes. Sensitive genotypes also showed rapid increases in enzyme activities involved in ROS and RNS metabolism. However, the measured antioxidant enzyme activities were higher in the tolerant genotypes than in the sensitive genotypes in which increased rapidly following drought stress. The results suggest that drought stress causes differential responses to oxidative and nitrosative stress in maize genotypes with tolerant genotypes with slower reaction and less ROS and RNS production than sensitive ones. These differential patterns may be utilized as potential biological markers for use in marker assisted breeding.
Highlights
Drought stress dramatically limits crop growth and development, and can trigger a significant decrease in crop yield and quality
Drought stress resulted in a visible loss of turgor with curling and wilting symptoms apparent in seedling leaves during the period of drought, and this phenotype gradually worsened with continuing decreases in soil water content (SWC) over time
Photosynthetic parameters were affected by drought treatment in all tested lines, decreases in photosynthesis rate (Pn), Gs and transpiration rate (Tr) and increase in Ci values may imply that the plant is subjected to stress conditions [54,55], and it can be proposed that the inhibition of photosynthesis was caused by the hypersensitive early stomata closure, with more pronounced occurrence in sensitive genotypes [56]
Summary
Drought stress dramatically limits crop growth and development, and can trigger a significant decrease in crop yield and quality. This is especially evident for maize grown as a summer crop in the Southern U.S as drought stress in combination with high temperatures aggravate stress severity, and exacerbate Aspergillus flavus colonization leading to pre-harvest aflatoxin contamination [1,2,3]. Plants can adapt to drought stress by regulating the homeostasis of many biochemical pathways related to water transport, transpiration, osmotic balance, signal transduction, antioxidant mechanisms, and the protection or degradation of proteins [1,5,6,7]. Despite the damaging potential of these molecules, ROS are continuously produced at a low level by some metabolic processes in plants [10]
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