Transcriptional and physiological insights into calcium-mediated waterlogging tolerance in peach

Waterlogging (WL) stress severely affects the growth and productivity of fruit crops. Cytosolic calcium (Ca 2+ ) is recognized as a secondary messenger that initiates adaptive responses to environmental stresses. However, the mechanisms by which exogenously applied Ca 2+ enhances WL tolerance remain poorly understood. In this study, we investigated whether exogenous Ca 2+ , applied as calcium chloride (CaCl 2 ) and calcium oxide nanoparticles (CaO-NPs), might mitigate WL-induced damage in peach ( Prunus persica ) seedlings. We found that both Ca 2+ formulations significantly alleviated WL-induced growth inhibition, restored photosynthetic efficiency, and maintained root system architecture and metabolic activity. Two Ca 2+ treatments markedly reduced intracellular superoxide (SOD) and hydrogen peroxide accumulation, thus attenuating membrane lipid peroxidation and electrolyte leakage. Hormonal profiling demonstrated that Ca 2+ suppressed excessive abscisic acid and salicylic acid accumulation while restoring jasmonate homeostasis under WL conditions. Furthermore, at the transcriptional level, Ca 2+ enhanced stress tolerance by upregulating the expression of genes encoding antioxidant ( PpSOD ; and peroxidase , PpPOD ), photosynthetic ( photosystem II subunit Q , PpPsbQ ; and photosystem I subunit K , PpPsaK ), and Ca 2+ ( CBL-interacting protein kinases , PpCIPK5 and PpCIPK11 ). In line with reduced oxidative stress, Ca 2+ also adaptively downregulated genes related to the fermentative pathway ( alcohol dehydrogenase , PpADH ; and lactate dehydrogenase , PpLDH ), indicating a shift away from anaerobic metabolism. Notably, comparative analysis revealed that ionic Ca 2+ and CaO-NP treatments resulted in largely similar outcomes under WL conditions, with only marginal differences in some parameters. Taken together, these results indicate that Ca 2+ -associated signaling is a putative regulatory network underlying adaptive responses to WL stress in woody fruit crops.