Low-Frequency Polarized Electric Field Enhances Postharvest Disease Resistance in Grapes by Activating Ca²⁺-Dependent Signaling and Phospholipid Metabolism, and Promoting Ca²⁺-Mediated Reinforcement of Cellular Structure

This study investigated the effects of a low-frequency polarized electric field (LFPEF) on postharvest disease resistance and storage quality of grapes. LFPEF treatment (3 h/d) significantly reduced weight loss, suppressed Botrytis cinerea lesion expansion, and maintained fruit firmness by reinforcing cell wall integrity and enhancing defense-related enzyme activities. Mechanistic analyses indicated that LFPEF activated Ca²⁺ signaling, promoted calcium accumulation, and upregulated calcium sensor genes, thereby contributing to membrane stabilization. Moreover, transient overexpression of Calcineurin B-like protein 2 (CBL2) enhanced fruit resistance, and yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays suggested a potential interaction between CBL2 and phospholipase A2 (PLA2). In line with this, LFPEF stimulated phospholipid metabolism, as reflected by elevated PLA and PLC activities and accumulation of phosphatidic acid, phosphatidylinositol, phosphatidylcholine, and phosphatidylethanolamine, alongside reduced phosphatidylglycerol and PLD activity. Collectively, these results demonstrate that LFPEF enhances grape resistance and storage quality through coordinated activation of Ca²⁺ signaling and phospholipid metabolic pathways.