Abstract: Early-season Satsuma mandarin fruit produced in Chongqing are usually harvested when the flesh reaches the acceptable internal maturity standards, while the peel is still green. In order to solve this problem, ethylene degreening treatment is widely used in the citrus industry. However, the light color and poor organoleptic quality of ethylene-degreened Satsuma mandarin fruit affect its acceptance by consumers. The effect of light on the coloration of ethylene-degreened Satsuma mandarin fruit was investigated in our previous study, and we found that treatment with 300 lx, 450 nm blue light-emitting diode (LED) irradiation was effective in improving the coloration of ethylene-degreened Satsuma mandarin fruit. The underlying mechanism was explored from the perspective of carotenoid metabolism. Since the color formation of mandarin fruit is determined by both chlorophyll and carotenoids, the effect of blue LED irradiation on chlorophyll metabolism in ethylene-degreened mandarin fruit was investigated in this study. The results showed that combined treatment with blue light and ethylene promoted the degradation of chlorophyll a, chlorophyll b, pheophytin a, pheophorbide a, and pheophorbide b and thus accelerated fruit color change by up-regulating the expression of the chlorophyll degradation-related genes CcRCCR and CcNYC1 and down-regulating the expression of the chlorophyll synthesis-related genes CcCAO, CcChIH and CcMPEC in Satsuma mandarin fruit. These results provide a theoretical reference for understanding the regulation mechanism of blue LED light irradiation on the coloration of ethylene-degreened Satsuma mandarin fruit.

Key words: Satsuma mandarin fruit; blue light-emitting diode irradiation; ethylene degreening; chlorophyll