Oak (Quercus robur L.) seedlings were grown in pots under controlled conditions and submitted to 34 days of flooding followed by two-week drainage. Roots were significantly affected with reduced extension and dry weight accumulation. After drainage, biomass production of adventitious roots markedly increased in flooded seedlings. Flooding induced a sharp decrease in NO3--N content in the soil especially in the bottom of pots. NH4+-N concentrations increased significantly but at less level compared to NO3--N decreases. During flooding, root nitrate reductase activity (NRA) was similar to controls while leaf NRA was always below that of controls. The flooded roots maintained amino acid synthesis despite the nitrate depletion in soil. By contrast, leaf amino acid content decreased significantly in flooded seedlings especially at day 34. In flooded seedlings, the transfer of amino acid from cotyledons was disrupted but the transfer capacity was restored after drainage. Relationships between nitrate reduction and changes in soil mineral nitrogen availability are discussed.