Low-NaCl pretreatment promotes seedling growth of Chinese white radish under water deficit via osmotic and energy regulation

Pretreatment with sodium chloride (NaCl) has been reported to enhance plant tolerance to subsequent water deficit; however, the underlying energy-related mechanisms, particularly during early seedling development, remain insufficiently understood. This study aimed to (1) evaluate the effects of low NaCl and water-deficit conditions on growth, water status, chlorophyll and proline contents in Chinese white radish seedlings, and (2) investigate the influence of NaCl pretreatment on photosynthetic activity, respiratory CO₂ production, sugar accumulation, and cellular energy status under water-deficit condition. Seeds were germinated in sand culture and watered with 0, 10, or 20 mM NaCl for 4 days, followed by transferring the seedlings to 0, − 0.5, or − 1.0 MPa mannitol solutions for 3 days. Growth parameters, water status, chlorophyll and proline contents were assessed in 7-day-old seedlings. Low-NaCl pretreatment enhanced shoot height, fresh weight, yield, water content, degree of succulence and proline content under water deficit. The optimal conditions (10 mM NaCl and − 0.5 MPa) were subsequently used to evaluate Hill’s reaction activity, CO₂ production, sugar contents, and energy status. NaCl-pretreated seedlings exhibited increased CO₂ production; higher fructose, glucose, and sucrose contents; elevated ATP/ADP and ATP/AMP ratios; and a higher adenylate energy charge under water deficit. Overall, the findings demonstrate that 10 mM NaCl pretreatment enhances the growth of Chinese white radish seedlings under water-deficit condition by improving osmotic regulation and maintaining energy homeostasis.