Abstract
The contents of flavonoids and other related components, in addition to the activities of related enzymes, such as phenylalanine ammonia-lyase (PAL), peroxidase (POD), chalcone synthase (CHS), and UDP-glucose:flavonoid 3-O-glucosyltransferase (UFGT), were determined in Ginkgo biloba L. leaves during leaf development. The results indicated that POD activity increased gradually in the early stages and reached its first activity peak in the beginning of Jul., the second one in late Aug., and the third one (the highest peak) in the middle of Oct. The changes in POD activity were irregular, and its activity was maintained at a low level in the early stages. However, it increased rapidly from the middle of Sep., and reached its highest value in the middle of Oct. Three peaks were obtained for PAL activity. The first peak, with the highest value was in early to middle Jul. The second one, with the lowest value, was in late Aug., and the last one, with a higher value and the longest period, was after the middle of Sep. UFGT activity had a speedy increase in the early stages and continued to increase after May. However, the net increase remained low. CHS activity was enhanced during all stages and showed two obvious peaks. The first time was in early Jul., and the other, with a higher value, was in the middle of Nov. Although PAL activity had a close relationship with the flavonoid content, no notable correlation could be identified between them. A significant correlation between CHS activity and the flavonoid content showed that CHS was one of the key enzymes involved in flavonoid biosynthesis. The relationship between flavonoid content and other related enzymes is discussed in this study.
Highlights
Ginkgo biloba L. is one of the most popular functional plants, especially used as a medicinal plant
When the highest peak appeared during Nov., the net change of flavonoid content (FC) was less than 1.5% in the first fifteen days
PPO and POD had some influences on flavonoid formation (FF), whereas UDP-glucose:flavonoid 3-O-glucosyltransferase (UFGT) seems to have no effect on flavonoid biosynthesis (FB)
Summary
Ginkgo biloba L. is one of the most popular functional plants, especially used as a medicinal plant. Extracts of G. biloba leaves contain some active compounds, such as flavonoids and terpene lactones, and can increase peripheral and cerebral blood flows (Rice-Evans et al, 1997; Smith and Luo, 2004). Numerous studies have focused on G. biloba leaf because flavonoid content (FC) in G. biloba leaf is higher than that in G. biloba seed. Approximately 38 types of flavonoids present in the leaf have been isolated (van Beek and Montoro, 2009). According to the knowledge gathered from other plant systems, more than 10 enzymes take part in the conversion process from phenylalanine to flavonoids in a plant. No direct data on flavonoid biosynthesis (FB) in G. biloba leaves are available, and only the changes of phenylalanine ammonia-lyase (PAL) activity in G. biloba leaf has been studied so far (Xu et al, 2008a)
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