Expression studies of Nrt2:1Np, a putative high‐affinity nitrate transporter: evidence for its role in nitrate uptake |
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| Authors: | Anne Krapp Vincent Fraisier Wolf&#;Rüdiger Scheible Alberto Quesada Alain Gojon Mark Stitt Michel Caboche Françoise Daniel&#;Vedele |
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| Institution: | ;1Biologie Cellulaire, INRA de Versailles, Route de St Cyr, F‐78026 Versailles Cedex, France,, ;2Botanisches Institut, Universität Heidelberg,Im Neuenheimer Feld 360, D‐69120 Heidelberg, Germany,,;3Departamento de Biología Experimental, Universidad de Jaén, 23071‐Jaén, Spain, and, ;4Biochimie et Physiologie Moleculaire des Plantes,ENSA‐M/INRA/UM2/CNRS URA 2133, F‐34060 Montpellier Cedex 1, France |
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| Abstract: | Expression of the gene Nrt2Np, which encodes a putative high-affinity nitrate transporter of Nicotiana plumbaginifolia was studied under variable physiological conditions. Nrt2Np is rapidly induced by very low nitrate concentrations and repressed by reduced nitrogen metabolites. Furthermore, Nrt2Np is expressed in coordination with other genes involved in nitrate assimilation (Nia, Nii). A deficiency in nitrate reductase activity, which is accompanied by high internal nitrate concentration and low levels of nitrogen metabolites, e.g. glutamine, leads to an overexpression of Nrt2Np, showing that high nitrate concentration per se does not repress Nrt2Np expression. By investigating plants with altered nitrate uptake properties, we showed a correlation between Nrt2 mRNA accumulation and 15N nitrate influx rates, providing the first evidence that the expression of Nrt2 correlates with the rate of nitrate uptake. In situ hybridization revealed a tissue-specific expression pattern. Nrt2Np mRNA accumulation is localized throughout all layers of the root tip, being highest in epidermal and endodermal cells. However, in mature root tissue, Nrt2 expression was detected mainly in the lateral root primordia and in the epidermis. |
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