NaHS immersion alleviates the stress effect of chromium(III) on alfalfa seeds by affecting active oxygen metabolism.

Objective: This study aimed to investigate the regulatory effects of exogenous hydrogen sulfide (H ₂ S) on seed germination, seedling growth, and reactive oxygen species (ROS) homeostasis in alfalfa under chromium (Cr) ion (III) stress.
Methods: The effects of 0-4 mM Cr(III) on the germination and seedling growth of alfalfa were first assessed. Subsequently, following seed NaHS immersion, the influence of H ₂ S on alfalfa seed germination and seedling growth under 2 mM Cr(III) stress was investigated, and the substance contents and enzyme activities associated with ROS metabolism were quantified.
Results: Compared to the control group, alfalfa plant germination was delayed under 2 mM Cr(III) stress for up to 48 h ( p  < 0.05). At 120 h, the total seedling length was approximately halved, and the root length was roughly one-third of the control. Treatment with 0.02-0.1 mM NaHS alleviated the delay in germination and root growth inhibition caused by 2 mM Cr(III) stress, resulting in an increased ratio of root length to hypocotyl length from 0.57 to 1 above. Additionally, immersion in 0.05 mM NaHS reduced hydrogen peroxide (H ₂ O ₂ ) and oxygen-free radicals (O ₂ ^{· -} ) levels ( p  < 0.05), boosted glutathione (GSH) levels ( p  < 0.05), and notably enhanced catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) activities ( p  < 0.05) compared to the 2 mM Cr(III) stress treatment group.
Conclusion: Seed immersion in NaHS mitigated the delay in germination and inhibition of root elongation under 2 mM Cr(III) stress. This effect is likely attributed to the regulation of intracellular ROS homeostasis and redox balance through enzymatic and non-enzymatic systems; thus, providing a potential mechanism for combating oxidative stress.