Comprehensive physiological, transcriptomic, and metabolomic analyses revealed that putrescine alleviates the response of grapes to salt-drought combined stress

Salt-drought combined (SD) stress presents substantial obstacles for grape cultivation. Polyamine compounds (PAs) are essential for boosting plant resilience against abiotic stressors. Herein, their role in alleviating SD stress and boost growth remains unexplored in grape plants. Here, we used 1-year-old ‘Sweet sapphire’ grape to investigate the effects of exogenous putrescine (Put), including the role of its biosynthetic precursors arginine (Arg) and ornithine (Orn), polyamine synthase inhibitors, dichloromethylarginine (DFMA), dichloromethylornithine (DFMO), and cycloethylamine (CHA) on SD responses. Under SD stress, grape leaves exhibited water loss, structural damage, membrane peroxidation, reduced photosynthesis, and inhibited growth. Conversely, the Arg, Orn, and Put treatments mitigated SD effects on grape growth by increasing photosynthesis, osmotic regulatory substances and endogenous PAs contents, and antioxidant enzymes activity. In contrast, DFMA, DFMO, and CHA further aggravated SD-induced damage to grapevines. Transcriptomic and metabolomic analyses indicated that SD activated the arginine and flavonoid biosynthetic pathways, whereas Put treatment further regulated the expression levels and metabolites of genes related to arginine and flavonoid biosynthesis in grapes, thereby alleviating the growth-limiting effects induced by SD stress. Overall, this study provides a crucial theoretical framework for enhancing SD stress resistance in grapes and advancing the development of the grape industry.