Effects of nitrate pulses on BnNRT1 and BnNRT2 genes: mRNA levels and nitrate influx rates in relation to the duration of N deprivation in Brassica napus L.
A de-repression mechanism based on the disappearance of 'signals' down-regulating N transporter activity has been proposed in the literature to explain the transient increase of NO(3)(-) uptake by the roots following N deprivation in higher plants. This hypothesis was investigated at the physiological and molecular levels by measuring NO(3)(-) influx into roots of Brassica napus L. grown under low or high external concentrations of KNO(3) following N deprivation. Parallel measurements were made of endogenous NO(3)(-), amino acid concentrations and abundance of mRNA for BnNRT1 and BnNRT2, genes encoding nitrate-inducible transport proteins. The effect of NO(3)(-) pulsing on NO(3)(-) transport components in N-deprived plants was also investigated by measuring influx of high- and low-affinity transport system (HATS and LATS) and assaying mRNA levels. Influx of NO(3)(-) via HATS and LATS, and transcript levels of BnNRT2 and BnNRT1 decreased with the duration of N deprivation. The results suggested that the absence of de-repression of NO(3)(-) influx and BnNRT2 gene expression following N starvation was related to a high amino acid status. Pulsing with NO(3)(-) induced a large increase in BnNRT2 mRNA level, but a comparatively small increase in NO(3)(-) influx via HATS. The level of BnNRT1 mRNA also increased, but there was no effect on LATS uptake activity. The absence of a strict correlation between the NO(3)(-) transport activity and the mRNA BnNRT1 and BnNRT2 levels is discussed in terms of possible post-transcriptional regulation by the amino acids.
Faure-Rabasse
Sandrine
S
Institut de Recherche en Biologie Appliquée, UMR INRA/UCBN de Physiologie et Biochimie Végétales, Esplanade de la Paix, Université de Caen, F-14032 Caen Cedex, France.
Le Deunff
Erwan
E
Lainé
Philippe
P
Macduff
James H
JH
Ourry
Alain
A
D000596:Amino Acids / Q000378:metabolism; D027321:Anion Transport Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D001693:Biological Transport, Active / Q000187:drug effects; D015152:Blotting, Northern; D029688:Brassica napus / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D003001:Cloning, Molecular; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D018698:Glutamic Acid / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism; D007700:Kinetics; D000091285:Nitrate Transporters; D009566:Nitrates / Q000378:metabolism / Q000494:pharmacology*; D009584:Nitrogen / Q000172:deficiency* / Q000494:pharmacology; D009587:Nitrogen Isotopes; D010940:Plant Proteins; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism; D018520:Plant Shoots / Q000187:drug effects / Q000378:metabolism; D012333:RNA, Messenger / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects
D000596:Amino Acids; D027321:Anion Transport Proteins; D029681:Arabidopsis Proteins; D018698:Glutamic Acid; D005973:Glutamine; D000091285:Nitrate Transporters; D009566:Nitrates; D009584:Nitrogen; D009587:Nitrogen Isotopes; D010940:Plant Proteins; D012333:RNA, Messenger; C101492:NRT1.1 protein, Arabidopsis; C477335:NRT2.1 protein, Arabidopsis