Ascorbic acid (AsA), an essential non-enzymatic antioxidant in plants, regulates development growth and responses to abiotic and biotic stresses. However, research on AsA’s role in cold tolerance remains largely unknown. Here, our study uncovered the positive role of AsA in improving cold stress tolerance in tomato seedlings. Physiological analysis showed that AsA significantly enhanced the enzyme activity of the antioxidant defense system in tomato seedling leaves and increased the contents of proline, sugar, abscisic acid (ABA), and endogenous AsA. In addition, we found that AsA is able to protect the photosynthetic system of tomato seedlings, thereby relieving the declining rate of chlorophyll fluorescence parameters. qRT-PCR analysis indicated that AsA significantly increased the expression of genes encoding antioxidant enzymes and involved in AsA synthesis, ABA biosynthesis/signal transduction, and low-temperature responses in tomato. In conclusion, the application of exogenous AsA enhances cold stress tolerance in tomato seedlings through various molecular and physiological responses. This provides a theoretical foundation for exploring the regulatory mechanisms underlying cold tolerance in tomato and offers practical guidance for enhancing cold tolerance in tomato cultivation.

Non-heading Chinese cabbage (NHCC) is a highly economically valuable leafy vegetable widely grown in Asian regions. However, it undergoes rapid leaf yellowing and wilting during postharvest storage, which subsequently cause rapid quality decline and loss of nutritional components. Abscisic acid (ABA) promotes postharvest leaf senescence, while hydrogen-rich water (HRW) is widely used in postharvest preservation due to its excellent antioxidant properties; yet, the mechanism through which they interact to regulate postharvest senescence in NHCC remains unclear. Herein we found that exogenous HRW effectively delayed dark- and ABA-induced postharvest leaf senescence in NHCC, significantly maintained chlorophyll content, inhibited oxidative damage, and preserve nutritional components such as soluble sugars and vitamin C. The underlying mechanism was HRW inhibiting chlorophyll degradation by repressing the expression of chlorophyll catabolic genes like NYC1, NYE1, and PPH1. Meanwhile, HRW effectively lowered the accumulation of MDA and H₂O₂, elevated both the enzymatic activities and transcript abundance of SOD and CAT, and downregulated the transcript levels of RbohB, RbohC, RbohD, and RbohE, thereby maintaining reactive oxygen species (ROS) homeostasis. In addition, HRW negatively regulated ABA biosynthesis by inhibiting the transcript levels of ABA1, ABA2 and ABA3, while promoting the transcription of CYP707A1, CYP707A2 and CYP707A3. It also dampened the transcript abundance of ABA signaling components including PYL5, ABI1, and ABF3, thus blocking ABA signal transduction and alleviating its senescence-promoting effect. Collectively, this study confirms that HRW mitigates leaf senescence induced under dark and ABA conditions in NHCC via multiple synergistic pathways.