Résumé
Alcohol dehydrogenase (ADH; alcohol: NAD oxidoreductase; EC 1.1.1.1) is a dimeric-zinc enzyme which catalyses the inter-conversion of acetaldehyde to ethanol, using NAD/NADH as a cofactor. This is the terminal step of glycolysis, leading to fermentative metabolism in anaerobic conditions. In this context, the evolution of this enzyme’s activity, and gene expression have been widely investigated in response to anaerobiosis in the plant kingdom, especially in organs such as roots, tubers, seeds and fruit (Kadowaki et al. 1988, Matton et al. 1990, Sun Chen and Chase 1993, Millar et al. 1994, Ke et al. 1994, Chung and Ferl 1999). ADH activity is generally low under normal oxygen tension, but strongly increases when the absence of oxygen leads to ethanolic fermentation. It appears to play an important role in the plant response to anaerobiosis, as ADH induction was generally detected in organs adapted to this stress. In maize, Gerlach et al. (1983) showed that ADH is fundamental to anaerobic survival for ADH null mutants. Paul and Ferl (1991) described the enhanced transcription of two genes responsible for an increased ADH synthesis. During oxygen deprivation, the assumed role of ADH is to reduce toxic acetaldehyde to ethanol and to recycle NADH to NAD, thereby allowing anaerobic glycolysis to be used as an energy-generating pathway. It could also be involved in cytoplasmic homeostasis, as the level of ADH activity is tightly regulated by pH, and as uncontrolled cytoplasmic acidosis is lethal (Roberts et al. 1984). ADH has also been implicated in the response to a wide range of other stresses, elicitors and also to abscisic acid (Christie et al. 1991, Constabel et al. 1990, Jarillo et al. 1993, Matton et al. 1990, de Bruxelles et al. 1996, Peters and Frenkel 2004).