Physiological and molecular adaptations of Citrus grandis roots to long-term copper excess revealed by physiology, metabolome and transcriptome. Citrus maxima

Little information is available on the physiological and molecular adaptations of plant roots to long-term copper (Cu) excess revealed by combined analysis of physiology, widely targeted metabolome and RNA-Seq. Citrus grandis seedlings were supplied six times weekly with nutrient solution at a Cu concentration of 400 (excessive Cu) or 0.5 (control) micromole for six months. Thereafter, excessive Cu impacts on gene expression, metabolites, cell wall (CW) materials and components, as well as some other physiological parameters in roots were examined. Although the abundances of many metabolites and the expression levels of some genes related to the detoxification of reactive oxygen and nitrogen species were elevated in RCu400, they could not protect these roots from oxidative damage. Also, we observed some similarities and differences in excessive Cu-responsive genes and metabolites between leaves and roots.