Dependence of Ethanolic Fermentation, Cytoplasmic pH Regulation, and Viability on the Activity of Alcohol Dehydrogenase in Hypoxic Maize Root Tips

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Abstract
We examined the role of alcohol dehydrogenase (ADH) in the metabolism and survival of hypoxic maize (Zea mays L.) root tips. The dependence of the rate of ethanolic fermentation, cytoplasmic pH, and viability on the activity of ADH in maize root tips during extreme hypoxia was determined. Maize lines with ADH activities differing over about a 200-fold range were studied. Effects of genetic background were controlled by comparing pairs of F4 progeny of crosses between mutant (low ADH activity) and reference inbred lines. The capacity of hypoxic root tips to perform ethanolic fermentation exhibited a dependence on ADH activity only at activities found in Adh 1 nulls. The ability of maize root tips to withstand prolonged and extreme hypoxia was like-wise independent of ADH activity, except at the lowest activities. Root tips that exhibited lower tolerance of hypoxia had more acidic cytoplasm during extreme hypoxia. We conclude that the activity of ADH in normal maize root tips does not limit the capacity for energy production via fermentation, and does not determine viability under extreme hypoxia. The significance of the induction of ADH activity in plants by hypoxia is discussed.