Effects of blue LED light irradiation on pigment metabolism of ethephon-degreened mandarin fruit

•Blue LED light improved peel color of ethephon-degreened mandarin fruit.•Blue LED light promoted chlorophyll degradation in ethephon-degreened fruit.•Blue LED light induced total carotenoid accumulation in ethephon-degreened fruit.•Induced β-cryptoxanthin accumulation might be the main reason for the deep color.•Genes expression related to pigments metabolism can partly explain this finding. To improve peel color of ethephon-degreened citrus fruit, in this study, the effects of blue light emiting diode (LED) light (450nm) irradiation on chlorophyll and carotenoid metabolism of ethephon-degreened mandarin fruit were evaluated. Deeper and faster coloration were observed in blue LED light-irradiated fruit, accompanied by the accumulation of carotenoid and the degradation of chlorophyll. Blue LED irradiation could shorten the degreening time of ethephon-degreened mandarin fruit. The accumulation of total carotenoid, lutein, violaxanthin, β-cryptoxanthin and zeaxanthin could well explain the faster coloration of the blue LED-irradiated mandarin fruit, while the accumulation of β-cryptoxanthin could well explain the deeper color of the blue LED-irradiated mandarin fruit. For chlorophyll metabolism, the increased expression of chlorophyll catabolism related genes (CitChlase, CitPao and CitRCCR), especially the increased expression of CitChlase might partly explain the sharply decrease of chlorophyll a and b in blue LED-irradiated fruit. However, it seems that both the expression levels of genes in metabolism of carotenoid and chlorophyll could only partly explain the changes in carotenoid and chlorophyll contents, more complex mechanisms might be interacting. Blue LED light may be a potential technique for improving the external color and commercial value of ethephon-degreened citrus fruit.