Effects of exogenous jasmonic acid on growth and physiological indices of alfalfa under chromium stress

Soil contamination by heavy metals is increasingly severe, particularly in eastern Inner Mongolia, China, where chromite mining has resulted in significant environmental issues due to heavy metal residues. Alfalfa, a common forage crop in the region, is considered an effective crop for remediating heavy metal contamination. However, the effectiveness of alfalfa alone in this context is limited. Jasmonic acid (JA), as a major phytohormone, plays an important role in regulating various physiological processes in plants; therefore, in this study, JA was added to remediate chromium contamination synergistically with alfalfa. The objective of this study was to investigate the synergistic effects of JA in combination with alfalfa for the remediation of Cr contamination. Specifically, the functional role of JA in modulating alfalfa growth and physiological responses under different Cr concentrations (1, 10, and 30 mg/L) was elucidated. JA application significantly reduced Cr accumulation in alfalfa seedlings by 49.70-87.37%, with mitigation efficacy dependent on Cr stress intensity: at 1 mg/L Cr, (0.1-1 μM) JA reduced the inhibitory effects on roots and stems by 74.86% and 270.91%, respectively. At 10 mg/L Cr, (0.5-1 μM) JA inhibited oxidative damage and reduced the levels of H₂O₂ and O₂^- by 61.19% and 14.91%, respectively. For 30 mg/L Cr, 0.5 μM JA maximized total chlorophyll synthesis (2.03-fold increase) and root cell viability (36.76%) while reducing MDA accumulation by 48.27%. Cluster analysis indicated that JA concentrations between 0.1-1 μM were most effective in alleviating 1 mg/L Cr stress, while 0.5-1 μM JA optimally mitigated the effects under 10 mg/L Cr stress, and 0.5 μM JA was most beneficial under 30 mg/L Cr stress. JA was found to be essential for maintaining normal metabolic functions and alleviating Cr-induced damage in alfalfa. This study highlights the potential of jasmonic acid as an effective agent for mitigating chromium stress in alfalfa and advances the understanding of its role in plant stress physiology. These findings provide valuable insights for improving crop resilience in heavy metal-contaminated environments. Future research should focus on the broader application of JA in different plant species and under different environmental stress conditions.