Phytohormone Response to Exogenous Nitric Oxide in Cucumber Under Low-Temperature Stress

To elucidate the comprehensive mechanism by which nitric oxide (NO) enhances low-temperature tolerance in cucumber, we utilized two cucumber cultivars (Jinyan No. 4 and Jinyou No. 1) as experimental materials. By integrating transcriptomic analysis with physiological indicators, we investigated the physiological and molecular mechanisms underlying the NO-mediated improvement of cold tolerance. Both molecular and physiological data revealed that phytohormone signal transduction and alpha-linolenic acid metabolism were significantly affected by low-temperature stress alone and in combination with exogenous SNP treatment in both cultivars. Under low-temperature stress, most transcripts associated with abscisic acid (ABA) biosynthesis, ABA signal transduction, and flavonoid biosynthesis were coordinately downregulated in cucumber. In contrast, transcripts related to secondary metabolism, lipid metabolism, glutathione biosynthesis, and hormone signal transduction-including salicylic acid (SA), ethylene (ETH), gibberellin (GA), and jasmonic acid (JA) pathways-were coordinately upregulated. Additionally, exogenous SNP was found to regulate both phytohormone signal transduction and endogenous hormone levels. These results suggest that exogenous NO improves low-temperature tolerance in cucumber seedlings primarily by modulating phytohormone signaling and secondary metabolism.