Fermentation Rates and Ethanol Accumulation in Relation to Flooding Tolerance in Rhizomes of Monocotyledonous Species

Fermentation capacity as measured by alcohol dehydrogenase (ADH) and lactate dehydrogenase (LDH) activity were estimated together with ethanol and lactate accumulation over a period of 15 d anoxia in rhizomes of six monocotyledonous species. With the exception of Iris germanica, all the species were characteristic wetland plants.
Under anoxia, an accumulation of ethanol took place in all species. Lactic fermentation was found to be of less importance in every case. The amount of ethanol accumulated depended on the ability of the rhizome to eliminate it from its tissues. Despite great variations in fermentative capacity as seen in the ADH measurements, the wetland species did not accumulate ethanol to concentrations greater than 30 µmol g-1 fresh weight. This represented a plateau above which the ethanol concentration did not rise even with continued anaerobic incubation. No such plateau of ethanol accumulation was found in the dryland species Iris germanica that accumulated ethanol steadily reaching concentrations of 70 µmol g-1 fresh weight.
If ethanol is toxic to higher plant tissues then the steady state condition of low ethanol accumulation found in wetland species will minimize this danger.