Temperature and water loss affect ADH activity and gene expression in grape berry during postharvest dehydration

Clusters of Aleatico wine grape were picked at 18 °Brix and placed at 10, 20, or 30 °C, 45% relative humidity (RH) and 1.5 m/s of air flow to dehydrate the berries up to 40% of loss of initial fresh weight. Sampling was done at 0%, 10%, 20%, 30%, and 40% weight loss (wl). ADH (alcohol dehydrogenase) gene expression, enzyme activity, and related metabolites were analysed. At 10 °C, acetaldehyde increased rapidly and then declined, while ethanol continued to rise. At 20 °C, acetaldehyde and ethanol increased significantly with the same pattern and declined at 40% wl. At 30 °C, acetaldehyde did not increase but ethanol increased rapidly already at 10% wl. At the latter temperature, a significant increase in acetic acid and ethyl acetate occurred, while at 10 °C their values were low. At 30 °C, the ADH activity (ethanol to acetaldehyde direction), increased rapidly but acetaldehyde did not rise because of its oxidation to acetic acid, which increased together with ethyl acetate. At 10 °C, the ADH activity increased at 20% wl and continued to rise even at 40% wl, meaning that ethanol oxidation was delayed. At 20 °C, the behaviour was intermediate to the other temperatures. lative expression of the VvAdh2 gene was the highest at 10 °C already at 10% wl in a synchrony with the ADH activity, indicating a rapid response likely due to low temperature. The expression subsequently declined. At 20 and 30 °C, the expression was lower and increased slightly during dehydration in combination with the ADH activity. This imbalance between gene expression and ADH activity at 10 °C, as well as the unexpected expression of the carotenoid cleavage dioxygenase 1 (CCD1) gene, opens the discussion on the stress sensitivity and transcription event during postharvest dehydration, and the importance of carefully monitoring temperature during dehydration.