Organic acid metabolism during grape berry development

The research conducted within the present project will result in a greater understanding of grape berry acidity, how it is achieved and how it is regulated during berry development. Berry acidity, the composition of tartaric (TA) and malic (MA) acids present in the berry during ripening, is critical for ensuring the suitability of berries for winemaking purposes, and in addition provides important organoleptic properties in wines of all ages.

Our earlier CRC Viticulture funded research identified a gene involved in TA synthesis, which was present only in berries that accumulate tartaric acid and switched on (transcribed) only during the period of TA accumulation. Moreover, when tested in the laboratory, the enzyme encoded by the gene was capable of specifically catalysing a key step in the conversion of L-ascorbic acid to TA. We sought to extend this work in the present project by undertaking further investigations of grapevine genes associated with tartaric acid synthesis and metabolism. We have used molecular and biochemical tools, in conjunction with extensive fieldwork over three growing seasons, to identify candidate genes for additional steps in the TA synthesis pathway. In addition, we have investigated the processes responsible for TA movement within berry cells, and thereby identified four candidate proteins that will in future be investigated more fully for their function in controlling vacuolar acid levels.