Phosphorus availability alleviates chilling injury through modulation of phosphorus metabolism and cold-responsive gene expression in cucumber (Cucumis sativus L.) fruit

Chilling stress is a major constraint in cucumber (Cucumis sativus L.) fruit, often causing chilling injury (CI) on the peel during low-temperature handling. This study investigated how phosphorus (P), an essential nutrient for plant metabolism, modulates fruit responses to chilling stress. Chilling stress induced the expression of multiple inorganic P (Pi)-responsive genes and altered P allocation toward organic P (Po), suggesting crosstalk between the chilling response and P homeostasis. To further examine the role of P in modulating the chilling response, exogenous KH₂PO₄ was applied to cucumber fruits. P-treated fruits showed significant CI mitigation, largely due to reducing oxidative stress without a concomitant increase in antioxidant activity. P supply increased Po levels, with no significant difference in Pi, suggesting that enhanced allocation to Po is a key acclimation strategy. Among Po fractions, metabolite P showed the most prominent accumulation, likely contributing to improved metabolic stability under chilling stress. Additionally, P-supplemented fruits exhibited elevated expression of cold-responsive genes (CsMPK3-like, CsICE1s, and CsCBF) and Pi-related regulators (CsPHR1-1 and CsSPX1-2), suggesting their coordinated regulation by P availability. Overall, these findings suggest P as a potential modulator of chilling stress responses and demonstrate its role in alleviating CI through coordinated metabolic and signaling adjustments in cucumber fruit.