Mechanism of Carotenoid Accumulation in Citrus Fruit

Citrus is a complex source of carotenoids with the largest number of carotenoids found in any fruit. Carotenoid concentration and composition vary greatly among citrus varieties. Satsuma mandarin (Citrus unshiu Marc.) predominantly accumulates β-cryptoxanthin in the juice sacs. Valencia orange (Citrus sinensis Osbeck) predominantly accumulates violaxanthin isomers in the juice sacs. Lisbon lemon (Citrus limon Burm.f.) accumulates low level of carotenoids in the juice sacs. To elucidate the carotenoid accumulation in citrus fruit maturation, the expression of genes related to carotenoid biosynthesis and catabolism was investigated in the three citrus varieties exhibited different carotenoid profile. The results showed that the carotenoid accumulation during citrus fruit maturation is highly regulated by the coordination of the expression for the genes related to carotenoid biosynthesis and catabolism in both flavedo and juice sacs. ‘Tamami’ is a hybrid between ‘Kiyomi’ tangor (Citrus unshiu Marc. × Citrus sinensis Osbeck) and ‘Wilking’ mandarin (Citrus nobilis Lour. × Citrus deliciosa Ten.). To elucidate the mechanism of the accumulation of β-cryptoxanthin in ‘Tamami’, a variety accumulating higher β-cryptoxanthin than Satsuma mandarin, the expression of genes related to carotenoid biosynthesis and catabolism was investigated in the juice sacs of ‘Tamami’. The results showed that the mechanism of β-cryptoxanthin accumulation in ‘Tamami’ was similar to that in Satsuma mandarin. Furthermore, in the recent studies, possible factors, which regulate carotenoid concentration and composition in citrus juice sacs were investigated in vitro.