Accumulation of red apocarotenoid β-citraurin in peel of a spontaneous mutant of huyou (Citrus changshanensis) and the effects of storage temperature and ethylene application

Red-peeled huyou has a distinct red peel color due mainly to the presence of red apocarotenoid β-citraurin as well as the increase in amount of total carotenoids. The expression level of carotenoid cleavage dioxygenase 4b1 (CCD4b1) accounted for 99.0% of total transcript abundance of CCD4s in red-peeled huyou peel and was nearly 100 times higher than that in ordinary huyou. β-Citraurin accumulation and peel coloration was mostly favored at 15 °C but strongly inhibited at moderately high temperatures 20 °C and 25 °C. Exogenous ethylene application for 3 d had no obvious effect on β-citraurin accumulation in red-peeled huyou but holding fruit at moderately higher temperatures (20 °C and 25 °C) for 3 d had a significant adverse effect on β-citraurin accumulation. The expression of phytoene synthase 1 (PSY1) and CCD4b1 was higher at 10 °C and 15 °C and significantly lower at 20 °C and 25 °C. The mechanisms governing the accumulation of β-citraurin are discussed.