Alisma plantago-aquatica L. (Alismataceae) and Sium latifolium L. (Apiaceae) can grow both under flooding and moderate water deficit. Activity of alcohol dehydrogenase (ADH) plays a critical role in the metabolism of plants under hypoxia participating in fermentation of sugars to ethanol - the primary mechanism of energy production in hypoxic roots. This study was aimed to characterize localization of ADH activity and its isozyme spectrum in roots of the aerial-aquatic and terrestrial plants. Cytochemical localization revealed that the ADH activity was associated with the root tip in aerial-aquatic plants. The ADH spectrum consisted of two isozymes in the A. plantago-aquatica roots and three isozymes in the S. latifolium ones. At the same time ADH activity was not observed in the roots of terrestrial plants. However, the weak ADH activity appeared in the roots of terrestrial plants after temporary flooding in time-dependent manner. The established changes in ADH gene expression in different water environment demonstrate its significant role in plant phenotypic plasticity.