Transfer of nodulated and non-nodulated plants grown in vermiculite to hydroponic culture without soil was used to study waterlogging and nitrogen transport in the xylem of soybean. Non-aeration, aeration or aeration with nitrogen gas were used to obtain different levels of oxygen in the culture solutions. Ureides, the principal form of nitrogen transport in nodulated plants, were considerably reduced in waterlogged plants or after transfer to water-culture, especially when not aerated or aerated with nitrogen gas. Aeration of the water-culture following a period of non-aeration allowed some recovery of ureides, as did the return of plants to drained vermiculite. Although smaller changes in the total amino acid fraction were observed for the different treatments, marked changes occurred in the composition depending on the treatment imposed. A high proportion of asparagine and low glutamine characterised non-nodulated plants grown on nitrate, or nodulated plants subsequently fed nitrate. A higher level of glutamine and lower level of asparagine characterised nodulated plants dependent on nitrogen fixation. High levels of aspartic acid characterised plants transferred to water-culture with aeration, especially in N-deficient solution, while alanine and serine were very prominent in non-aerated or hypoxic water-culture. These changes also occurred in non-nodulated plants and plants kept in vermiculite in a flooded condition. Some of the changes in transport were accompanied by similar changes in the free amino acid fraction of the roots. It is suggested that an alteration in asparagine metabolism may underlie the changes in amino acid transport in the xylem associated with waterlogging. (C) Editions scientifiques et medicales Elsevier SAS.3710767773