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 degrees Brix and placed at 10, 20, or 30 degrees 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 degrees C, acetaldehyde increased rapidly and then declined, while ethanol continued to rise. At 20 degrees C. acetaldehyde and ethanol increased significantly with the same pattern and declined at 40% wl. At 30 degrees 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 degrees C their values were low. At 30 degrees 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 degrees C, the ADH activity increased at 20% wl and continued to rise even at 40% wl, meaning that ethanol oxidation was delayed. At 20 degrees C, the behaviour was intermediate to the other temperatures. The relative expression of the VvAdh2 gene was the highest at 10 degrees 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 degrees 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 degrees 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. (C) 2011 Elsevier Ltd. All rights reserved.