Résumé
The metabolic changes of mature grape berries during periods of anoxia and upon return to air were examined using two cultivars. Glutamate declined during anoxia, together with a corresponding accumulation of γ-aminobutyrate (GABA). The reverse occurred during a 24 h period of air. Total adenine nucleotide (AdN), ATP level, and adenylate energy charge (AEC) all declined during periods of anoxia but showed a reversible pattern upon subsequent aeration. However, aerobic recovery of metabolite levels was not observed when the duration of anoxia at 30°C exceeded 6 d. Accumulated ethanol during anoxia (up to 0.22 M) triggered a further increase in the rate of ethanol synthesis when stressed berries were returned to air. Ethanol may be the principal determinant governing the ability of grapes to withstand and recover from anoxic stress. We propose that the imbalance between aerobic and fermentative pathways may be due to the ability of ethanol to impair mitochondrial membrane function and uncouple oxidative phosphorylation, the rate of anaerobic respiration being insufficient to meet energy requirements.