Physiological, biochemical, and transcriptomic analysis characterized high-temperature and high-humidity combined stress response mechanisms in cucumber (Cucumis sativus L.)

In protected cultivation systems, high-temperature and high-humidity (HTHH) conditions frequently co-occur during spring, summer, and autumn seasons, severely compromising cucumber yield and quality. Most previous studies focused on heat stress as an isolated factor, while the interactive effects of temperature-humidity combined stress remained poorly characterized, particularly regarding underlying molecular mechanisms. This study systematically investigated the physiological, biochemical and molecular responses of cucumber seedlings to individual and combined temperature-humidity stresses. Integrated physiological and molecular analyses revealed that HTHH synergistically impaired tissue integrity through vascular bundle disorganization and mesophyll collapse, disrupted stomatal regulation via abnormal guard cell dynamics, and induced chloroplast ultrastructural degradation. These structural alterations correlated with exacerbated oxidative damage and irreversible organelle dysfunction. Our findings established a physiological-structural framework explaining cucumber seedling susceptibility to concurrent HTHH stress, providing critical insights for enhancing stress resilience in crops under multifactorial environmental constraints.