Effect of the combination of ethylene and red LED light irradiation on carotenoid accumulation and carotenogenic gene expression in the flavedo of citrus fruit

The effects of ethylene and red light-emitting diode (LED) light (660 nm) on the accumulation of carotenoid and expression of genes related to carotenoid biosynthesis were investigated in the flavedo of Satsuma mandarin. The results showed that the contents of β-cryptoxanthin, all-trans-violaxanthin, 9-cis-violaxanthin and lutein were simultaneously increased along with the total carotenoid accumulation by the red LED light. With the ethylene treatment, the contents of β-carotene and β-cryptoxanthin were increased, while the content of lutein was decreased in the flavedo. The suppression of lutein accumulation by ethylene was inhibited when the ethylene treatment was performed under the red LED light. With the combination of ethylene and red LED light treatments, the contents of β-cryptoxanthin and lutein were simultaneously increased. Gene expression results showed that simultaneous increases in the expression of CitPSY, CitPDS, CitZDS, CitCRTISO, CitLCYb1, CitLCYb2, CitLCYe, CitHYb, and CitZEP contributed to the accumulation of β-cryptoxanthin and lutein in the treatment of ethylene combined with red LED light. The results presented might provide new strategies to enhance the commercial and nutritional value of citrus fruit.