Effects of light and plant hormones on regreening in flavedos of Ponkan mandarin in vitro

In this study, the regulation of regreening in the flavedos of citrus fruit was investigated in vitro. The results showed blue light was much more effective than red light for inducing regreening in citrus fruit. In the blue light treatment, the up-regulation of chlorophyll biosynthetic genes and the down-regulation of chlorophyll degradation genes led to the re-accumulation of chlorophyll in the flavedos of mature fruit. In addition, we found that blue light was a necessary factor for GA-induced regreening in citrus fruit. Under blue light, GA treatment accelerated the re-accumulation of chlorophyll in the flavedos. In contrast to GA, ABA treatment did not induce regreening under blue light, and the flavedos kept in orange color. Compared with the blue light treatment alone, the contents of chlorophyll a, chlorophyll b, and total chlorophyll were decreased by the combination of ABA and blue light treatments. The results presented in this study suggested that blue light and GA are positive regulators for inducing regreening, while ABA is a negative regulator of regreening in the flavedo of mature citrus fruit.