Mechanism of Carotenoid Accumulation in Citrus Fruit

Abstract

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.

Enzymatic Formation of β-Citraurin from β-Cryptoxanthin and Zeaxanthin by Carotenoid Cleavage Dioxygenase4 in the Flavedo of Citrus Fruit

“…According to changes in the color of the flavedo, the ripening process of citrus fruits can be divided into three stages: a green stage (September), a transition stage (from October to November), and a mature stage (from December to January; Kato, 2012). As shown in Figure 3A, two varieties of Satsuma mandarin, Yamashitabeni-wase and Miyagawa-wase, showed a color break gradually from the transition stage.…”

“…The pathway of carotenoid biosynthesis has been well documented in various plant species, including Arabidopsis (Arabidopsis thaliana; Park et al, 2002), tomato (Lycopersicon esculentum; Isaacson et al, 2002), pepper (Capsicum annuum; Bouvier et al, 1998), citrus (Citrus spp. ; Kato et al, 2004Kato et al, , 2006Rodrigo et al, 2004;Rodrigo and Zacarías, 2007;Kato, 2012;Zhang et al, 2012a), and apricot (Prunus armenaica; Kita et al, 2007). Genes encoding the enzymes in the carotenoid biosynthetic pathway have been cloned, and their expression profiles have also been characterized (Fig.…”

Pigments in Citrus

“…8.2a). The most common carotenes responsible for fruit and flower colors are α-carotene, β-carotene, and lycopene; and common xanthophylls are lutein, zeaxanthin, and violaxanthin [2,6,24,27,28]. In plants, carotenoids also serve as potent antioxidants against photooxidation, as essential precursors for biosynthesis of certain hormones, as attractive colorants for flower pollination and fruit/seed dispersal, and/ or as responsive substances for environmental adaptation [32][33][34].…”

“…Most carotenoid biosynthesis genes have been identified and the pathway well-characterized in model plants and major crops [32,35], and in citrus as well [28,43,47]. All the genes encoding catalytic enzymes in plants are from nuclear genomes, while the biosynthesis process takes place in plastids, as shown in a schematic diagram of the main steps in the carotenoid biosynthesis pathway ( Fig.…”

“…8.1 and 8.2). In general, phytoene is colorless, while α-carotene, β-cryptoxanthin, and zeaxanthin may contribute more toward yellow, β-carotene, lutein, and violaxanthin toward orange, and lycopene toward red in a range of light pink to dark red depending on its accumulated concentrations [2,5,24,[27][28][29][30][31].…”