## 4 Discussion
Both green-fleshed kiwifruit and yellow-fleshed kiwifruit are green in color when immature, and their carotenoid content is stable [36]. As the fruit matures, chlorophyll in the mesocarp of yellow-fleshed kiwifruit is degraded into colorless metabolites, and the mesocarp color changes to yellow as carotenoids become dominant. However, in green-fleshed kiwifruit, the degree of chlorophyll degradation is far less than that in yellow-fleshed kiwifruit, and therefore green-fleshed kiwifruit contains higher chlorophyll at maturity and the mesocarp remains green in color [36; 37]. In conclusion, the main factor contributing to the yellow color of kiwifruit mesocarp is the degradation of chlorophyll rather than carotenoid synthesis. In this study, chlorophyll content decreased during fruit development and ripening, and bagging treatment accelerated the rate of chlorophyll degradation. Carotenoid content was relatively stable in the later stages of development, and bagging reduced the accumulation of carotenoids. Notably, chlorophyll and carotenoid contents increased after debugging, indicating that light plays an important role in chlorophyll and carotenoid metabolism. Recent studies on chlorophyll and carotenoid metabolism have also been reported. The metabolism of chlorophyll and carotenoids in plants is a dynamic process involving synthesis and degradation [11]. Chlorophyll degradation was shown to result in chlorosis of the mesocarp, in response to the combined effect of downregulated chlorophyll-synthesis genes and upregulated chlorophyll-degradation genes [6]. In this study, with the development of kiwifruit, the expression of chlorophyll-synthesis genes was slightly upregulated, whereas its degradation genes were significantly upregulated. Although bagging treatment inhibited the expression of chlorophyll-synthesis and -degradation genes, the upregulation trend of chlorophyll-degradation genes remained unchanged, which may be the reason for chlorosis during the development of 'jinyan' kiwifruit. Studies have shown that SGR proteins play a key role in the degradation of plant chlorophyll [38]. Chlorophyll degradation in kiwifruit is regulated by SGR proteins [10]. The chlorophyll content and expression of chlorophyll-metabolism genes in green and yellow kiwifruit during development showed that \(SGR\) was positively correlated with chlorophyll degradation [6]. In this study, it was also found that the upregulation of \(AcSGR\) expression during fruit development was much higher than that of other chlorophyll-degradation genes, which once again proved that chlorophyll degradation in kiwifruit is regulated by the \(SGR\) gene. Similar to chlorophyll metabolism, carotenoid synthesis and degradation are also regulated by the associated genes. In this study, bagging reduced the expression of most genes related to carotenoid metabolism, which is consistent with previous research results of studies on peaches [39]. Previous studies on kiwifruit have shown that \(\beta\)-carotene is the main carotenoid in kiwifruit [40], and its content is positively correlated with the expression of the \(LCYB\) gene [40], indicating that \(LCYB\) may play an important role in the process by which light affects the accumulation of carotenoids in kiwifruit. The effect of light on AsA content has been confirmed in many plants. A bagging study on kiwifruit showed that bagging reduces the AsA content of _A. deliciosa, A. chinensis_, and _A. eriantha_[4]. The results of the present study also support this conclusion. The L-galactose pathway is the dominant biosynthesis pathway of AsA in plants, and all structural genes in this pathway have been identified [16]. Analysis of the promoter sequences of these structural genes revealed that light-responsive elements were distributed on most gene promoters and their activity could be induced by light [18]. Studies on kiwifruit showed that only _GallDH_, _GalUR_, and _DHAR_ expression were affected by bagging, while a study on 'Jinyan' (_A.