Physiological changes and expression characteristics of ZIP family genes under zinc deficiency in navel orange (Citrus sinensis)

Zinc (Zn) deficiency is widespread among citrus plants, but information about the mechanisms for Zn deficiency response in these plants is scarce. In the present study, different navel orange (Citrus sinensis (L.) Osbeck) leaves with various yellowing levels were sampled in our experimental orchard, and upon estimation of nutrient contents, Zn deficiencies were diagnosed as mild, moderate, and severe. Further analysis of chlorophyll content, photosynthetic characteristics, antioxidant enzyme activities, and expression levels of Zn/Iron-regulated transporter-like protein (ZIP) family genes were conducted in the sampled Zn-deficient leaves. The results showed that chlorophyll contents and net photosynthetic rate (Pn) seemed to decrease with reduced Zn contents. In addition, comparison of severe Zn-deficient and normal leaves revealed that activities of peroxidase (POD) and catalase (CAT) increased significantly, whereas that of Zn-containing enzymes such as Cu/Zn superoxide dismutase (Cu/Zn-SOD) significantly reduced with decreasing Zn contents. As expected, expression of the ZIP family genes, ZIP1, ZIP3, and ZIP4, was induced by Zn deficiencies. These results deepen our understanding of Zn deficiency in citrus plants as well as provide useful preliminary information for further research.