Drought affects crop developmentnand growth. To explore the physiological effects of drought stress on soybean, HeiNong44 (HN44) and HeiNong65 (HN65) varieties were used as experimental materials and PEG-6000 was used as the osmotic medium. The antioxidant enzyme activity, osmotic adjustment substance content, antioxidant capacity, and endogenous hormone content of the two soybean varieties were studied under different drought degrees and different treatment durations. Drought stress caused significant physiological changes in soybean. The antioxidant enzyme activities, osmoregulation substance content, and total antioxidant capacity (T-AOC) of HN65 and HN44 showed an increasing trend under mild and moderate drought, however, they first increased and then decreased under severe drought conditions. Following the extension of treatment time, malondialdehyde (MDA) showed an increasing trend. As drought increased, gibberellin (GA) content showed a decreasing trend, while abscisic acid (ABA), salicylic acid (SA), and zeatin nucleoside (ZA) content showed an increasing trend. The auxin (IAA) content of the two varieties showed opposite change trends. In short, drought had a significant impact on the physiology of these two soybean varieties; however, overall, the drought resistance of HN65 was lower than that of HN44. This study provides a research theoretical basis for addressing the drought resistance mechanism and the breeding of drought resistant soybean varieties.

Excessive plant height is an important factor that can lead to lodging, which is closely related to soybean yield. Gibberellins are widely used as plant growth regulators in agricultural production. Gibberellic acid (GA₃), one of the most effective active gibberellins, has been used to regulate plant height and increase yields. The mechanism through which GA₃ regulates internode elongation has been extensively investigated. In 2019 and 2020, we applied GA₃ to the stems, leaves, and roots of two soybean cultivars, Heinong 48 (a high-stalk cultivar) and Henong 60 (a dwarf cultivar), and GA₃ was also applied to plants whose apical meristem was removed or to girded plants to compare the internode length and stem GA₃ content of soybean plants under different treatments. These results suggested that the application of GA₃ to the stems, leaves, and roots of soybean increased the internode length and GA₃ content in the stems. Application of GA₃ decreased the proportion of the pith in the soybean stems and primary xylem while increasing the proportion of secondary xylem. The apical meristem is an important site of GA₃ synthesis in soybean stems and is involved in the regulation of stem elongation. GA₃ was shown to be transported acropetally through the xylem and laterally between the xylem and phloem in soybean stems. We conclude that the GA₃ level in stems is an important factor affecting internode elongation.

Soybean stem elongation and thickening are related to cell wall composition. Plant morphogenesis can be influenced by blue light, which can regulate cell wall structure and composition, and affect stem growth and development. Here, using proteomics and metabolomics, differentially expressed proteins and metabolites of hypocotyls grown in the dark and under blue light were studied to clarify the effects of blue light on the cell wall structure and carbohydrate metabolism pathway of soybean hypocotyls. Results showed that 1120 differential proteins were upregulated and 797 differential proteins were downregulated under blue light treatment, while 63 differential metabolites were upregulated and 36 differential metabolites were downregulated. Blue light promoted the establishment of cell wall structure and composition by regulating the expression of both the enzymes and metabolites related to cell wall structural composition and nonstructural carbohydrates. Thus, under blue light, the cross-sectional area of the hypocotyl and xylem were larger, the longitudinal length of pith cells was smaller, elongation of the soybean hypocotyl was inhibited, and diameter was increased.

Increasing planting density is among the most effective ways to increase soybean yield, but high planting density increases lodging risks in soybean plants. To examine the effects of shading on soybean plant lodging, the tall cultivar Heinong 48 (HN48) and dwarf cultivar Henong 60 (HN60), two soybean cultivars with large plant height differences (approximately 40 cm), were selected, and their internode lengths were measured under different planting densities in 2019 to determine the key internode influencing lodging. In 2020, we treated soybean plants with different shading treatments to examine the morphology, anatomical structure and stem fiber composition of the fifth internode, changes in the GA₃ (gibberellic acid) content, and relative expression of GA₃-related enzyme genes in the stem under different shading conditions. The results showed that as the planting density increased, the lengths of the internodes changed significantly, starting from the fifth internode. Under different shading conditions, the length of the fifth internode increased for both cultivars, but the diameter and the diameter-to-length ratio decreased; the area of the xylem decreased, and the pith cells stretched more longitudinally and were more orderly; the lignin, cellulose, and hemicellulose contents decreased; the GA₃ content in the stem increased, and the expression levels of GmGA3ox6, GmGA20ox1-D, and GmGA2ox4 enzyme genes were all upregulated; and the change in PSN treatment was more significant than other treatments. Therefore, the fifth internode was the key internode that affected lodging in soybean plants, shading could increase the GA₃ content significantly in soybean stems, and the increase in GA₃ content was positively correlated with the shaded area. This study provides a new direction for future research on lodging resistance in densely planted or intercropped soybean plants.

Blue light serves as a critical environmental cue regulating Glycine max (soybean) stem morphology, yet the hormonal mechanisms underlying varietal differences remain unclear. Previous studies have highlighted the role of blue light in modulating plant architecture, but the specific hormone interactions driving morphological divergence between soybean varieties remain underexplored. Two soybean varieties with contrasting stem phenotypes—Henong 60 (HN60, tall) and Heinong 48 (HN48, dwarf)—were subjected to 0% (full light) and 30% (shade) transmittance conditions, supplemented with blue light (450 nm, 45.07 ± 0.03 μmol·m⁻²·s⁻¹). Stem anatomical traits (xylem area, cell length), hormone profiles, and proteomic changes were analyzed. Grey correlation analysis quantified relationships between hormone ratios and plant height. Blue light increased soybean stem xylem area and diameter while reducing plant height and cell longitudinal length. This treatment concurrently reduced growth-promoting hormones (gibberellin A₃ (GA₃), indole-3-acetic acid (IAA), brassinolide (BR)) and increased growth-inhibiting hormones (salicylic acid (SA), jasmonic acid (JA), strigolactones (SLs)), thereby inhibiting stem elongation. Although exogenous GA₃ promoted hypocotyl elongation, it failed to counteract blue-light-induced inhibition. Proteomic analysis identified 16 differentially expressed proteins involved in hormone signal transduction pathways. Grey correlation analysis highlighted cultivar-specific hormone ratio impacts: GA₃/JA, GA₃/SA, and BR/SLs significantly influenced HN60 plant height, while GA₃/SLs, IAA/SLs, and BR/SLs were critical for HN48, demonstrating highly significant positive correlations. The differential sensitivity of growth-promoting/inhibiting hormone ratios to blue light drives varietal morphological divergence in soybean stems. This study establishes a hormonal regulatory framework for blue-light-mediated stem architecture, offering insights for crop improvement under light-limited environments.