During the anaerobic germination of rice (Oryza sativa L.), nitrate is translocated from the caryopsis and assimilated into the coleoptile (R. Reggiani, M. Mattana, N. Aurisano, A. Bertani [1993] Plant Cell Physiol 34: 379-383). Using antibodies against nitrate and nitrite reductases, proteins with the expected molecular mass were recognized by western blot analysis in extracts from 8-d-old rice coleoptiles. Both enzymes are de novo synthesized in 6- to 8-d-old seedlings, as shown by immunoprecipitation of radiolabeled proteins from young plants grown in the presence of [35S]methio-nine. The anaerobic synthesis of both enzymes was enhanced by the addition of 5 mM KNO3. The effect of exogenous nitrate on the expression of the corresponding genes in anaerobic rice coleoptiles was revealed by the analysis of their transcripts. The importance of the expression of these enzymes during the anaerobic development of rice seedlings is discussed.