Abstract
Ascorbic acid (AsA), known as vitamin C, is an essential nutrient for humans and mainly absorbed from food. Tea plant (Camellia sinensis (L.) O. Kuntze) leaves can be a dietary source of AsA for humans. However, experimental evidence on the biosynthesis, recycling pathway and distribution of AsA during leaf development in tea plants is unclear. To gain insight into the mechanism and distribution of AsA in the tea plant leaf, we identified 18 related genes involved in AsA biosynthesis and recycling pathway based on the transcriptome database of tea plants. Tea plant leaves were used as samples at different developmental stages. AsA contens in tea plant leaves at three developmental stages were measured by reversed-phase high-performance liquid chromatography (RP-HPLC). The correlations between expression levels of these genes and AsA contents during the development of tea plant leaves were discussed. Results indicated that the l-galactose pathway might be the primary pathway of AsA biosynthesis in tea plant leaves. CsMDHAR and CsGGP might play a regulatory role in AsA accumulation in the leaves of three cultivars of tea plants. These findings may provide a further glimpse to improve the AsA accumulation in tea plants and the commercial quality of tea.
Highlights
(PMI)[18], phosphomannose mutase (PMM)[19], GDP-d-mannose-3′,5′-epimerase (GME)[20], GDP-d-mannose pyrophosphorylase (GMP)[21], GDP-l-galactose phosphorylase (GGP)[22], l-galactose-1-P phosphatase (GPP)[23]; l-galactose dehydrogenase (GalDH)[24], and l-galactono-1,4-lactone dehydrogenase (GalLDH)[25]
The ascorbic acid (AsA) content was measured at three leaf developmental stages in three tea plant cultivars by RP-HPLC (Figs 2 and 3)
By analyzing the expression levels of 18 genes, which were involved in the AsA biosynthesis and recycling pathways
Summary
(PMI)[18], phosphomannose mutase (PMM)[19], GDP-d-mannose-3′,5′-epimerase (GME)[20], GDP-d-mannose pyrophosphorylase (GMP)[21], GDP-l-galactose phosphorylase (GGP)[22], l-galactose-1-P phosphatase (GPP)[23]; l-galactose dehydrogenase (GalDH)[24], and l-galactono-1,4-lactone dehydrogenase (GalLDH)[25]. Arabidopsis lines overexpressing miox[4], a key gene in the myo-inositol pathway, showed an obvious increase in the AsA content[16]. Overexpressing a strawberry GalUR gene in Arabidopsis resulted in a two- to three-fold increase in AsA levels[14]. L-Gal pathway played a predominant role in AsA biosynthesis in peel and pulp of citrus fruits[40]. Based on the different contents of AsA, the three tea plant cultivars (‘Huangjinya’, ‘Anjibaicha’, and ‘Yingshuang’) were used as suitable samples for this research, and were used as samples in gene expression analyses. The related genes that involved in the biosynthesis and recycling pathways of AsA were identified from the tea plant transcriptome database[41]. The AsA content in tea plant leaves at three developmental stages in ‘Yingshuang’, ‘Huangjinya’, and ‘Anjibaicha’ were recorded. This study will provide useful information for exploring of improving the content of AsA in the tea plants
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