Involvement of nitrate reduction in the tolerance of tomato (<Emphasis Type="Italic">Solanum lycopersicum</Emphasis> L.) plants to prolonged root hypoxia

The putative role of nitrate and nitrate reductase in the tolerance to prolonged hypoxia was investigated in tomato plants. Nitrogen nutrition has been modified either by deprivation of nitrate or by addition of tungstate—an inhibitor of nitrate reductase (NR)—in the culture medium. In the absence of nitrate as well as in the presence of tungstate, plant growth was significantly disturbed. In the presence of nitrate, the growth of hypoxic plants maintained, nitrate absorption and NR activity increased and a significant release of nitrite into the medium was observed. This mechanism of nitrate reduction, called nitrate respiration, could be an alternative pathway to oxygen-dependent respiration during root hypoxia and a transient adaptation of tomato roots to hypoxic conditions.