Seed Priming with Chitosan Improves Germination Characteristics Associated with Alterations in Antioxidant Defense and Dehydration-Responsive Pathway in White Clover under Water Stress

Water stress decreases seed-germination characteristics and also hinders subsequent seedling establishment. Seed priming with bioactive compounds has been proven as an effective way to improve seed germination under normal and stressful conditions. However, effect and mechanism of seed priming with chitosan (CTS) on improving seed germination and seedling establishment were not well-understood under water-deficit conditions. White clover (Trifolium repens) seeds were pretreated with or without 5 mg/L CTS before being subjected to water stress induced by 18% (w/v) polyethylene glycol 6000 for 7 days of germination in a controlled growth chamber. Results showed that water stress significantly decreased germination percentage, germination vigor, germination index, seed vigor index, and seedling dry weight and also increased mean germination time and accumulation of reactive oxygen species, leading to membrane lipid peroxidation during seed germination. These symptoms could be significantly alleviated by the CTS priming through activating superoxide dismutase, catalase, and peroxidase activities. In addition, seeds pretreated with CTS exhibited significantly higher expression levels of genes encoding dehydration-responsive transcription factors (DREB2, DREB4, and DREB5) and dehydrins (Y2K, Y2SK, and SK2) than those seeds without the CTS priming. Current findings indicated that the CTS-induced tolerance to water stress could be associated with the enhancement in dehydration-responsive pathway during seed germination.