Coumarin alleviates copper toxicity in citrus leaves by reducing damage to growth, cell walls, plasma membranes, and related metabolism, while maintaining copper and calcium homeostasis

Using sweet orange (Citrus sinensis (L.) Osbeck cv. Xuegan) seedlings as materials, the study investigated the effects of COU supply on gene expression and metabolite profiling, CW Fourier transform infrared (FTIR) spectra, and some related physiological parameters in leaves, as well as Ca and Cu homeostasis in leaves and CWs. The aim of this study was to corroborate the hypothesis that COU supply alleviated Cu toxicity in citrus leaves through the coordinated actions of following several aspects: (a) maintaining the homeostasis of Ca and Cu, as well as the structure and function of CWs and plasma membrane in leaves; (b) alleviating Cu excess-induced leaf senescence and inhibition of growth and reducing the impairment of Cu excess to primary and secondary metabolisms in leaves; and (c) enhancing the ability to maintain a balance between ROS production and scavenging.