| Summary: | Tartaric and malic acids are the predominant organic acids of grape
berries, and are important for fruit and wine quality. Tartaric acid, despite
having been found in several plant species, accumulates to a significant
level uniquely in the grape berry. It arises through the metabolism of
ascorbic acid (Vitamin C), and while many of the intermediates of the
tartaric acid biosynthesis pathway have been determined, the enzymes
responsible are still largely unknown. Malic acid is integrated in
complex primary metabolism, and displays developmental changes in
net accumulation and degradation through transport and metabolism
of the acid. The sensitivity of malic acid metabolism to environmental
conditions also causes seasonal variation in grape berry acidity. We
are investigating four aspects of organic acid metabolism in grapes
to advance the current knowledge of organic acid metabolism and
fruit acidity. Firstly, to uncover novel enzymes involved in tartaric acid
synthesis, we identified a candidate grapevine gene that can be used for
recombinant expression and functional characterisation. To determine
how the metabolism of tartaric and malic acids are controlled in grape,
we screened the concentration of these acids from numerous grapevine
populations, to assist the discovery of genes linked to acidity. To identify
transporters and transcription factors that regulate malate release from
the vacuole during berry ripening, we have cloned candidate genes
for functional characterisation. And fourthly, to determine the effect of
elevated temperature on organic acid metabolism, we have conducted
controlled atmosphere experiments using potted grapevines.
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