Mechanism of nitrogen release from roots of intact wheat plants (Triticum aestivum L.)

Abstract

It is hypothesised that a substantial proportion of nitrogen released by roots of entire plants into the soil are amino acids which are transported from shoot to root via phloem and from the phloem released into the root apoplast. From here amino acids may diffuse directly into the outer solution (soil or nutrient solution). Alternatively, amino acids extruded into the root apoplast may be retrieved via proton H+/co-transport This membrane transport is dependent on H+ which are provided by the plasmalemma H+ ATPase. Consequently, in line with our hypothesis conditions which influence the activity of the plasmalemma H+ pump may also influence the nitrogen release from roots into the outer medium. Thus, vanadate which inhibits the plasmalemma H+ pump or conditions which impair ATP provision for the H+ ATPase (high temperature or waterlogging), led to an increased nitrogen release. Conversely, fusiccocin which stimulates the H+ ATPase led to a depressed nitrogen release. We suggest that amino acids play a major role in nitrogen release by roots of entire plants and in line with our hypothesis the release of amino acids is mainly a diffusion, of which the rates mainly depend on the amino acid concentration in the root apoplast.