Methionine explains the dehydration sensitivity and tolerance in the seeds of two sister Panax species

Seed dehydration tolerance is a critical physiological trait determining post-harvest survival and species dispersal. While methionine (Met) enhances plant stress adaptation, its role in seed dehydration tolerance remains poorly defined. This study employed integrated transcriptomic and metabolomics analyses to compare Met metabolism during seed development in dehydration-tolerant Panax vietnamensis var. fuscidiscus and dehydration-sensitive Panax notoginseng, sister species exhibiting similar morphology but divergent dehydration tolerance despite equivalent maturity timing. Present study identified significantly higher (P < 0.01) Met accumulation in tolerant seeds at maturity. This divergence was driven by developmentally upregulated expression of key Met biosynthesis enzymes-cystathionine γ-synthase (CGS), methionine synthase (MS), and S-adenosylmethionine synthetase (SAMS) in P. vietnamensis var. fuscidiscus, contrasting with downregulation in P. notoginseng. Consequently, tolerant seeds exhibited superior antioxidant enzyme (SOD, POD, CAT) activity and glutathione-mediated reactive oxygen species (ROS) scavenging capacity during dehydration. Crucially, exogenous application of the Met synthesis inhibitor DL-propargylglycine (PAG) to tolerant P. vietnamensis var. fuscidiscus seeds suppressed Met accumulation, reduced antioxidant enzyme activity, impaired glutathione system function, compromised membrane integrity (increased electrolyte leakage), and diminished seed vigor and germination under dehydration stress. These results demonstrate that developmentally regulated Met metabolism, mediated by CGS, MS, and SAMS, critically governs seed dehydration tolerance. Met acts as a critical metabolite, enhancing tolerance primarily by bolstering redox homeostasis (via elevated antioxidant and glutathione system activity) and contributing to osmotic adjustment. This study elucidates a key molecular mechanism underlying dehydration tolerance variation in seeds and provides a theoretical foundation for improving storage strategies, particularly for recalcitrant species.