, Volume 196, Issue 2, pp 191-199

Regulation of mineral nitrogen uptake in plants

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Abstract

In the biosphere plants are exposed to different forms of N, which comprise mineral and organic N forms in soils as well as gaseous NH3, NOx, and molecular N2 in the atmosphere. The form of N uptake is mainly determined by its abundance and accessibility, which make \({\text{NO}}_{{\text{3}}^{\text{1}} } \) and \({\text{NH}}_{{\text{4}}^{\text{ + }} } \) the most important N forms for plant nutrition under agricultural conditions. With minor importance, the form of N uptake is also subject to plant preferences, by which plants maintain their cation/anion balance during uptake. However, some species seem to have an obligatory preference which even prevents their growth on certain other N sources. In general, uptake of a certain N form closely matches the growth-related demand of the plant, at least when N transport to the root surface is not limiting. In addition, many plants accumulate large pools of N during vegetative growth which are remobilized in the generative stage. As a consequence, systems responsible for N transport need to be tightly regulated in their expression and activity upon sensing N availability and plant demand. Employing the tools of molecular genetics, the first plant genes encoding transporters for inorganic N have recently been isolated and characterized. These data can now complete the wealth of physiological and nutritional studies on N uptake. The present article will focus on the uptake of \({\text{NO}}_{{\text{3}}^{\text{1}} } \) and \({\text{NH}}_{{\text{4}}^{\text{ + }} } \) into root cells and tries to link data derived from physiological, genetic and molecular studies.