Cold Plasma Treatment Enhances Drought Tolerance of Alfalfa (Medicago sativa L.) Seeds by Modulating Physiological Responses and Transcriptomic Profiles

Drought stress is a major limiting factor for alfalfa (Medicago sativa L.) production in arid and semi-arid regions. Cold plasma treatment has emerged as a promising physical technology for improving seed germination and stress tolerance, but its underlying mechanisms remain poorly understood. In this study, alfalfa seeds were treated with cold plasma (plasma discharge voltage: 0, 5, 10, 15 kV) for 5 min and exposed to PEG 6000 stress at 0, 5, 10, and 15%. Results showed that cold plasma treatment significantly alleviated the inhibitory effects of drought stress on seed germination, with the Plasma-15 kV treatment exhibiting the highest germination potential and germination rate compared to the control (p < 0.05). Plasma treatment enhanced the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), while reducing malondialdehyde (MDA) content (p < 0.05), indicating mitigated oxidative damage under drought conditions. Transcriptomic analysis revealed that cold plasma regulated the expression of genes involved in the MAPK signaling pathway and other drought-responsive pathways, leading to metabolic reallocation (Q < 0.05) and enhanced drought tolerance. In conclusion, 5 min of Plasma-15 kV treatment effectively enhances drought tolerance via physiological and transcriptional regulation, providing an eco-friendly strategy for alfalfa cultivation in dry regions.