The expression of carotenoid biosynthetic genes in sweet pepper (
Capsicum annuum L.) fruit during ripening and effects of light irradiation on fruit ripening were investigated. Fruits were harvested at the beginning of ripening, followed by light irradiation at a photosynthetic photon flux density of 100 μmol・m
−2・s
−1. Gene expressions of phytoene synthase (
Psy), β-carotene hydroxylase (
CrtZ-2), and capsanthin/capsorubin synthase (
Ccs) were markedly induced after 1 day of light irradiation. Each expression was 207, 8, and 6-times higher than the dark control, respectively. Other carotenoid biosynthetic genes: phytoene desaturase (
Pds), ζ-carotene desaturase (
Zds), lycopene β-cyclase (
LcyB), zeaxanthin epoxidase (
Ze), and violaxanthin de-epoxidase (
Vde), were also induced to 2–3-fold higher than the dark control. Light-irradiated fruits reached full redness in five days. These results suggest that light irradiation of harvested fruits induces a marked increase in the expression of
Psy and other carotenoid biosynthetic genes such as
CrtZ-2 and
Ccs, followed by the accumulation of capsanthin in the sweet pepper fruit.
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