L-tartaric acid synthesis from vitamin C in higher plants.
The biosynthetic pathway of L-tartaric acid, the form most commonly encountered in nature, and its catabolic ties to vitamin C, remain a challenge to plant scientists. Vitamin C and L-tartaric acid are plant-derived metabolites with intrinsic human value. In contrast to most fruits during development, grapes accumulate L-tartaric acid, which remains within the berry throughout ripening. Berry taste and the organoleptic properties and aging potential of wines are intimately linked to levels of L-tartaric acid present in the fruit, and those added during vinification. Elucidation of the reactions relating L-tartaric acid to vitamin C catabolism in the Vitaceae showed that they proceed via the oxidation of L-idonic acid, the proposed rate-limiting step in the pathway. Here we report the use of transcript and metabolite profiling to identify candidate cDNAs from genes expressed at developmental times and in tissues appropriate for L-tartaric acid biosynthesis in grape berries. Enzymological analyses of one candidate confirmed its activity in the proposed rate-limiting step of the direct pathway from vitamin C to tartaric acid in higher plants. Surveying organic acid content in Vitis and related genera, we have identified a non-tartrate-forming species in which this gene is deleted. This species accumulates in excess of three times the levels of vitamin C than comparably ripe berries of tartrate-accumulating species, suggesting that modulation of tartaric acid biosynthesis may provide a rational basis for the production of grapes rich in vitamin C.
School of Agriculture, Food, and Wine, University of Adelaide, Adelaide, SA 5005, Australia.
Seth
S
DeBolt
Douglas R
DR
Cook
Christopher M
CM
Ford
D001205:Ascorbic Acid / Q000378:metabolism*; D001483:Base Sequence; D002384:Catalysis; D003001:Cloning, Molecular; D017931:DNA Primers; D020224:Expressed Sequence Tags; D020869:Gene Expression Profiling; D017343:Genes, Plant; D008969:Molecular Sequence Data; D010944:Plants / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013644:Tartrates / Q000378:metabolism*; D014158:Transcription, Genetic
D017931:DNA Primers; D013644:Tartrates; D001205:Ascorbic Acid; C029768:tartaric acid