Effect of Postharvest Temperature and Ethylene on Carotenoid Accumulation in the Flavedo and Juice Sacs of Satsuma Mandarin (Citrus unshiu Marc.) Fruit

The effect of postharvest temperature (5, 20, and 30 °C) and ethylene at different temperatures (20 and 5 °C) on carotenoid content and composition and on the expression of the carotenoid biosynthesis-related genes was investigated in the flavedo and juice sacs of Satsuma mandarin (Citrus unshiu Marc.) fruit. Under an ethylene-free atmosphere, storage at 20 °C rapidly increased the carotenoid content in flavedo and maintained the content in juice sacs. In contrast, storage at 5 and 30 °C gradually decreased the content in juice sacs but slowly increased that in flavedo. Under an ethylene atmosphere, storage at 20 °C enhanced the carotenoid accumulation in flavedo more dramatically than found under an ethylene-free atmosphere with distinct changes in the carotenoid composition but did not noticeably change the content and composition in juice sacs. In contrast, storage at 5 °C under an ethylene atmosphere repressed carotenoid accumulation with changes in the carotenoid composition in flavedo but did not clearly change the carotenoid content in juice sacs. Under an ethylene-free atmosphere, differences in the gene expression profile among the temperatures were observed but were not well-correlated with those in the carotenoid content in flavedo and juice sacs. Under an ethylene atmosphere, in flavedo, the gene expression of phytoene synthase (PSY) and phytoene desaturase (PDS) was slightly higher at 20 °C but lower at 5 °C than under an ethylene-free atmosphere. At 20 °C, the gene expression of several carotenoid biosynthetic enzymes promoted by ethylene seemed to be responsible for the enhanced accumulation of carotenoid in flavedo. In contrast, at 5 °C, the repressed gene expression of PSY and PDS by ethylene seemed to be primarily responsible for the repressed accumulation of carotenoid in flavedo. In juice sacs, the small response of the gene expression to ethylene seemed to be responsible for small changes in carotenoid accumulation under an ethylene atmosphere.