Foliar application of 1-methylcyclopropene (1-MCP) alleviates heat-induced yield loss in cotton by improving physiological function of the leaf subtending to cotton boll

Heat stress (HT) severely impairs the physiological activity of the leaf subtending to cotton boll (LSCB), causing severe yield loss. Although 1-methylcyclopropene (1-MCP) is known to potentially enhance heat tolerance in cotton, its physiological mechanisms involved remain unclear. To investigate this, a two-year pot experiment was conducted under normal temperature (NT, 32/24°C) and high temperature (HT, 42/34°C) conditions, during the flowering and boll forming stages, and LSCB were sprayed with distilled water or a 400 μmol L −1 concentration of 1-MCP. HT severely reduced seed cotton yield by 77.5–79.9% and increased the boll abscission rate compared to NT. The foliar application of 1-MCP effectively alleviated HT-induced yield loss, resulting in increases of 101.4–141.7% and a decrease in the boll abscission rate relative to HT. However, the final yield, boll weight, and boll number in the HT+ 1-MCP treatment group remained significantly lower than those in the NT group. Physiological analyses revealed that 1-MCP mitigated HT-induced photoinhibition in LSCB, enhanced photosynthetic efficiency by increasing Fv/Fm, ΦPSII, and the electron transport rate (ETR), and reduced non-stomatal limitations to photosynthesis. Additionally, 1-MCP improved carbon partitioning by promoting sucrose accumulation. Furthermore, HT+ 1-MCP enhanced the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), reduced oxidative damage, and modulated hormone homeostasis, notably suppressing the ethylene precursor 1‑aminocyclopropane‑1‑carboxylic acid (ACC) while elevating abscisic acid (ABA) and salicylic acid (SA) levels. Structural equation modeling indicated that 1-MCP enhanced yield by both directly and indirectly improving LSCB function, by which facilitating through osmotic adjustment, antioxidant activity, and hormone homeostasis. Consequently, antioxidant-mediated optimization could support sucrose accumulation and carbohydrate allocation to the cotton bolls. These findings elucidate how 1-MCP sustains the LSCB functions and carbohydrate supply under HT, providing a physiological basis for its application as a field strategy to enhance cotton's heat tolerance. • 1-Methylcyclopropene application increased seed cotton yield under high temperature. • 1-Methylcyclopropene protect the leaf subtending to cotton boll from photoinhibition. • 1-Methylcyclopropene optimize carbon partitioning, favoring sucrose allocation to bolls. • 1-Methylcyclopropene enhance antioxidant capacity and coordinate hormonal homeostasis. • 1-Methylcyclopropene can be used as a field-compatible strategy to enhance cotton thermotolerance.