Plant Physiology Preview
Published on January 13, 2006; 10.1104/pp.105.075721
Received December 16, 2005
Returned for revision January 5, 2006
Accepted January 5, 2006
A central role for the nitrate transporter NRT2.1 in the integrated morphological and physiological responses of the root system to N limitation in Arabidopsis thaliana
Tony Remans , Philippe Nacry *, Marjorie Pervent , Thomas Girin , Pascal Tillard , Marc Lepetit , and Alain Gojon
Laboratoire de Biochimie & Physiologie Moléculaire des Plantes UMR 5004 INRA/CNRS/ENSAM/UM2, 2 place Viala, F-34060 Montpellier cedex 1 France
* Corresponding author; email: nacry{at}ensam.inra.fr.
Up-regulation of high-affinity transport system (HATS) for NO3- and stimulation of lateral root (LR) growth are two important adaptive responses of the root system to N limitation. Up-regulation of the NO3- HATS by N starvation is suppressed in the atnrt2.1-1 mutant of Arabidopsis thaliana, deleted for both NRT2.1 and NRT2.2 nitrate transporter genes. We then used this mutant to determine whether lack of HATS stimulation affected the response of the root system architecture (RSA) to low NO3- availability. In Ws wild-type plants, transfer from high to low NO3- media resulted in contrasting responses of RSA, depending on the level of N limitation. Moderate N limitation (transfer from 10 mM to 1 or 0.5 mM NO3-) mostly led to an increase in the number of visible laterals, while severe N stress (transfer from 10 mM to 0.1 or 0.05 mM NO3-) promoted mean LR length. The RSA response of the atnrt2.1-1 mutant to low NO3- was markedly different. After transfer from 10 mM to 0.5 mM NO3-, the stimulated appearance of LRs was abolished in atnrt2.1-1 plants, while the increase in mean LR length was much more pronounced than in Ws. These modifications of RSA mimicked those of Ws plants subjected to severe N stress, and could be fully explained by the lowered NO3- uptake measured in the mutant. This suggests that the uptake rate of NO3-, rather than its external concentration, is the key factor triggering the observed changes in RSA. However, the mutation of NRT2.1 was also found to inhibit initiation of LR primordia in plants subjected to N limitation, independently of the rate of NO3- uptake by the whole root system, and even of the presence of added NO3- in the external medium. This indicates a direct stimulatory role for NRT2.1 in this particular step of LR development. Thus, it is concluded that NRT2.1 has a key dual function in coordinating root development with external NO3- availability, both indirectly through its role as a major NO3- uptake system that determines the N uptake-dependent RSA responses, and directly through a specific action on LR initiation under N-limited conditions.
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