Morphological, physiological, enzymatic and molecular responses of maize varieties to drought stress

Maize subspecies of commercial importance, including popcorn (Zea mays everta), sugar maize (Zea mays saccharata), and dent maize (Zea mays indentata), are widely produced and consumed. Given that maize is a plant with high water demand, drought is the main factor limiting maize production. The present study examined the effects of drought stress on maize plants, including plant height, leaf area, fresh and dry weight of the plant, chlorophyll content, membrane durability index, malondialdehyde and hydrogen peroxide and leaf relative water content, turgor loss, proline content, antioxidant enzyme activities and HSP70 and HSP90 gene expression characteristics. These were examined according to differences between subspecies. In response to increasing drought stress, plant height, leaf area, fresh and dry weight, and chlorophyll content decreased, while electrolyte leakage increased. The greatest decrease in plant height was observed in sugar maize. The least negative change in leaf area was observed in dent maize under moderate drought conditions, followed by sugar and popcorn maize. While severe drought resulted in over 50% weight loss in plants, dent maize exhibited the least dry matter loss. Furthermore, dent maize showed the highest chlorophyll content at all irrigation levels. The effects of severe drought were more pronounced in sugar maize, which exhibited relatively high water content and turgor loss, membrane damage, enzyme activities, and HSP90 gene expression. Dent maize demonstrated the capacity to maintain its water content and turgor in both moderate and severe droughts, and exhibited effective utilization of its defense mechanism, evidenced by the maintenance of antioxidant enzyme activities at a consistent level despite a reduction in MDA and H2O2 accumulation. Despite the high levels of MDA and H2O2 in popcorn, the upregulation of antioxidant enzyme activities and HSP70 gene and protein expression indicates that the drought coping mechanism is activated. In particular, the positive correlation between HSP70 and proline, also HSP90 and enzyme activities is a significant finding for studies examining the relationships between HSPs and other stress response systems. Upon comprehensive evaluation of all examined characteristics, it was observed that dent maize had greater drought tolerance than other maize subspecies.