The alleviating effect of gibberellin seed soaking on salt stress in alfalfa
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Graphical Abstract
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Abstract
With the accelerating development and utilization of saline-alkali land resources in China, the cultivation area for alfalfa (Medicago sativa L.) in salinized soils has been continuously expanding. Enhancing salt tolerance during the seedling stage is crucial for successful establishment of alfalfa in challenging environments. Therefore, this study established three salt stress concentrations (0.3%, 0.6%, and 0.9%) combined with three gibberellic acid (GA3) seed soaking concentrations (50, 100, and 150 mg·L–1) to investigate the alleviative effects and mechanisms of exogenous GA3 on alfalfa under varying salt stress levels, while determining the optimal GA3 concentrations corresponding to different salinity conditions. The results demonstrated that: Under 0.3% salt stress, maximum shoot length (21.13% increase) and root length (18.96% increase) were achieved at 150 mg·L–1 GA3, while 100 mg·L–1 GA3 significantly enhanced fresh weight (10.49% increase) and dry weight (10.56% increase) compared to the control. Under 0.6% salt stress, 100 mg·L–1 GA3 optimized shoot length (14.88% increase) and dry weight (8.84% increase), whereas 50 mg·L–1 GA3 produced the longest roots (18.82% increase). Under 0.9% salt stress, 50 mg·L–1 GA3 significantly improved shoot length (15.7% increase), root length (10.75% increase), and dry weight (0.36% increase). Mechanistically, optimal GA3 concentrations alleviated salt stress by: 1) Enhancing antioxidant enzyme activities (superoxide dismutase, peroxidase, catalase). 2) Increasing endogenous phytohormone levels (auxin and salicylic acid). 3) Reducing stress markers — malondialdehyde (MDA), abscisic acid (ABA), chloride ions (Cl–), and sodium ions (Na+). A distinct inverse proportional relationship was observed between optimal GA3 concentrations and salt stress intensity. Specifically, under low salinity (0.3%), GA3 concentrations of 100–150 mg·L–1 were most effective. For moderate salinity (0.6%), 100 mg·L–1 GA3 proved optimal, while under high salinity (0.9%), a lower concentration of 50 mg·L–1 GA3 was sufficient to alleviate stress. This study confirmed that exogenous GA3 seed soaking effectively mitigates salt-induced phytotoxicity and promotes alfalfa seedling growth, with superior efficacy under low-to-moderate salt stress compared to severe stress conditions. These findings provide both a theoretical foundation and practical guidance for improving alfalfa cultivation efficiency in saline-alkali regions.
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