Abstract
Ascorbic acid (AsA), chlorophyll and carotenoid contents and their associated gene expression patterns were analysed in Actinidia chinensis ‘Hongyang’ outer pericarp. The results showed chlorophyll degradation during fruit development and softening, exposed the yellow carotenoid pigments. LHCB1 and CLS1 gene expressions were decreased, while PPH2 and PPH3 gene expressions were increased, indicating that downregulation of chlorophyll biosynthesis and upregulation of its degradation, caused chlorophyll degradation. A decrease in the expression of the late carotenoid biosynthesis and maintenance genes (LCYB1, LCYE1, CYP1, CYP2, ZEP1, VDE1, VDE2, and NCED2) and degradation gene (CCD1), showed biosynthesis and degradation of carotenoid could be regulatory factors involved in fruit development. Most genes expression data of L-galactose and recycling pathway were agreement with the AsA concentrations in the fruit, suggesting these are the predominant pathways of AsA biosynthesis. GMP1, GME1 and GGP1 were identified as the key genes controlling AsA biosynthesis in ‘Hongyang’ outer pericarp.
Highlights
The genus Actinidia shows a large variation in flesh colour
Ascorbic acid (AsA) content was highest at 30 days after anthesis (DAA) (215.15 mg 100 g-1fresh weight), declined rapidly until 100 DAA, and stabilised (Fig 1G), resembling the pattern of A. deliciosa ‘Hayward’ and A. eriantha [38]
The concentration of chlorophyll a, chlorophyll b and total chlorophyll decreased with fruit development but the concentration of total carotenoids did not markedly change, confirming that chlorophyll is degraded during fruit development and softening, leaving the yellow pigment of the carotenoids visible
Summary
The genus Actinidia (kiwifruit) shows a large variation in flesh colour. These colours are characteristic of the species or specific genotypes and have become an important feature of the fruit. The yellow- and red-fleshed cultivars have generated great interest throughout the industry worldwide. Previous report showed that the immature fruits of the yellowand red-fleshed kiwifruit cultivars are green [1]. In contrast to the green-fleshed species, chlorophyll degradation with the unmasking of the carotenoids, occurs in the yellow-fleshed Actinidia chinensis, concomitant with the fruit maturation and softening [2]. Some key genes involved in chlorophyll metabolism in kiwifruit are the chlorophyll biosynthesis gene
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