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Background: Drought is the main restricted agent for growth and development of soybean and the physiological characteristics of different parts of soybean leaves changed significantly. Methods: To explore the impacts of drought stress on the physiological characteristics of leaves in different parts of soybean, in this study, Williams 82 was used as the experimental material and drought stress was simulated by a watering nutrient solution containing 10% PEG-6000. Under different treatment time conditions, the superoxide dismutase (SOD) activity and proline (Pro) content in different parts of soybean leaves were determined. Result: The results indicate that the SOD activity and Pro content in the upper and bottom leaves of soybean increased significantly under drought stress conditions and with the increase in drought stress time, the SOD activity in the upper and bottom leaves of soybean increased first and then declined and the content of Pro increased gradually. In general, soybean relief drought damage by increasing SOD activity and Pro content under drought stress. This study offered the theoretical foundation for exploring the mechanism of soybean drought resistance. [ABSTRACT FROM AUTHOR]

Introduction: Soybean is the world's most important cultivated crop, and drought can affect their growth and, eventually, yields. Foliar application of mepiquat chloride (MC) can potentially alleviate the damage caused by drought stress in plants; however, the mechanism of MC regulation of soybean drought response has not been studied. Methods: This study investigated the mechanism of soybean drought response regulation by mepiquat chloride in two varieties of soybean, sensitive Heinong 65 (HN65) and drought-tolerant Heinong44 (HN44), under three treatment scenarios, normal, drought stress, and drought stress + MC conditions. Results and discussion: MC promoted dry matter accumulation under drought stress, reduced plant height, decreased antioxidant enzyme activity, and significantly decreased malondialdehyde content. The light capture processes, photosystems I and II, were inhibited; however, accumulation and upregulation of several amino acids and flavonoids by MC was observed. Multi-omics joint analysis indicated 2-oxocarboxylic acid metabolism and isoflavone biosynthetic pathways to be the core pathways by which MC regulated soybean drought response. Candidate genes such as LOC100816177, SOMT-2, LOC100784120, LOC100797504, LOC100794610, and LOC100819853 were identified to be crucial for the drought resistance of soybeans. Finally, a model was constructed to systematically describe the regulatory mechanism of MC application in soybean under drought stress. This study fills the research gap of MC in the field of soybean resistance. [ABSTRACT FROM AUTHOR]

Soybean is highly sensitive to drought stress during its flowering period. Heinong84 (HN84) and Hefeng46 (HF46) were planted in clay loam, silty loam, and sandy clay. We studied the effects of drought stress on the content of membrane lipid peroxides in flowering soybean leaves, the activity of antioxidant enzymes, and the activity of key enzymes of nitrogen metabolism under different soil conditions. Our results showed that soybean had clear physiological responses to drought stress. With increasing drought stress, the malondialdehyde, glutathione reductase, and glutathione peroxidase levels in soybean leaves increased continuously. Superoxide dismutase, peroxidase, glutamine synthase, and glutamate synthase levels increased with drought stress, reaching a maximum under moderate drought stress and then decreased; nitrate reductase activity decreased continuously. Under the condition of sufficient water, the performance of soybean in the three soils is almost the same, but there are differences under drought stress; particularly, soybean grown in clay loam shows the strongest drought resistance. In summary, the physiological state of soybean is easily affected by drought stress, which varies greatly among different cultivars and in different soil types. [ABSTRACT FROM AUTHOR]