Abstract: Improvement of plant architecture is an important way to fully exploit the potential of environmental resources of light, heat, and water in maize (Zea mays) production, and it is the basis of breeding targeting ideal plant type. This research studied the response mechanisms of drought tolerance related to plant architecture in maize. The plant architecture traits, stomatal morphologies, physiological metabolisms and photosynthesis characteristics of ear leaf, and yield were recorded for three different maize genotypes (Langhuang, Chang7-2, and TS141) with differing plant architecture under drought stress during the flowering stage. It was found that: 1) Leaf length, leaf width, leaf size, and leaf angle were decreased significantly, and leaf shape value and leaf orientation value of the three maize genotypes were increased significantly under drought stress. Moreover, genotype TS141, characterized as ‘flat’, had larger changes of these six plant architecture traits than genotypes characterized as ‘compact’ (Langhuang and Chang 7-2); 2) Drought stress increased the numbers of upper and lower epidermal stomata of all three maize genotypes, but decreased stomatal length and width. The change in stomatal number of TS141 was greater than for the other cultivars, and the size reduction was smaller; 3) Chlorophyll a, b, and (a+b) contents, and chlorophyll a:b ratio of TS141 were significantly decreased by drought. For the tested genotypes, chlorophyll a:b ratio had a smaller increase, and the other three traits had a smaller decrease in Langhuang and Chang 7-2 after drought stress than in TS141; 4) Stomatal conductance, net photosynthetic rate, the temperature of leaf thermocouples, transpiration rate, and RuBPCase activity decreased to different degrees in different genotypes, and intercellular CO₂ concentration increased to different degrees in the three tested maize genotypes under drought stress. However, compared with TS141, Langhuang and Chang 7-2 had smaller changes; 5) Yield per plant, ear weight, grain weight, 1000-seed weight, ear length, and kernel ratio of all three maize genotypes were decreased significantly under drought stress, and TS141 was affected more severely than Langhuang and Chang 7-2; 6) Principal component analysis and a heat map with hierarchical cluster analysis indicated that the relationships among these traits in maize under drought stress were complex and interrelated with each other, and could completely account for the differences in drought tolerance between the different plant architecture genotypes. Therefore, it is deduced from these results that plant architecture may be an important drought regulator that can be co-regulated with stomatal morphologies, physiological metabolisms, and photosynthetic characteristics to form the response mechanisms of drought tolerance. Moreover, because 'compact' maize genotypes displayed stronger drought tolerance, these types have better drought tolerance potential for use in future breeding work.

Key words: maize, plant architecture, drought stress, stomatal morphology, chlorophyll, photosynthetic characteristics, yield