In order to test the hypothesis that GABA could up-regulate nitrate uptake, the effect of exogenous supply of different amino acids was compared with control plants. Gln, Glu and Asn are known to act as inhibitors of nitrate uptake at the millimolar range in many species when supplied to the root nutrient solution ( Muller & Touraine 1992 ; Vid ). Therefore, roots were supplied with either 1 m m Gln, 1 m m Glu or 1 m m Asn, whereas two concentrations were tested for the GABA treatment, 100 µ m and 1 m m (Fig. 5). A positive and significant effect on 15 NO3 – influx was observed for 100 µ m (P < 0.05) and no significant effect for 1 m m GABA (P > 0.05)-treated plants compared with the control plants, whereas 15 NO3 – influx was significantly reduced by the Gln, Glu and Asn root treatments (Fig. 5a). The strongest negative effect on nitrate uptake was due to Glu (38% inhibition) followed by Asn (37% inhibition) and Gln (33% inhibition). In parallel, Northern blot analyses performed with mRNA extracted from the same amino acid treated plants confirmed previous results for all of the amino acids tested. Thus, BnNrt2 mRNA abundance was enhanced by 1.6- and 1.3-fold in response to 100 µ m and 1 m m GABA treatments, respectively. The Gln, Glu and Asn treatments reduced BnNrt2 mRNA abundance by 0.5-, 0.9- and 0.8-fold, respectively (Figs 5b & c).
Dialogue
Effects of exogenous supply of GABA, Gln, Glu and Asn on nitrate influx (a) and BnNrt2 gene expression (b and c) on 12 h nitrate deprived plants. Plants were supplied with 1 m m nitrate plus either 100 µ m or 1 m m GABA, 1 m m Gln, 1 m m Glu or 1 m m Asn for 12 h before measurement of 15 NO3 – influx and BnNrt2 transcript abundance. Influx and BnNrt2 transcript expression values are the means of six and two pots of 25 plants, respectively. Vertical bars indicate ± SE of the mean for n = 6 when larger than the symbol.
Endogenous concentrations out-of sources proteins was quantified for each treatment so you can find out if GABA inserted the root also to influence you’ll be able to relationship anywhere between endogenous amino acidic membership and you can nitrate increase otherwise Nrt2 mRNA peak (Desk 1). After a dozen h of exogenous have, endogenous intensity of each amino acid applied enhanced from the sources. For example, step 1 m yards GABA treatment improved supply GABA of the dos.24-fold compared with the new handle flowers (Table step one). But not, one hundred µ meters GABA and you may 1 meters meters Glu solutions unsuccessful to improve density quantities of most of the five amino acids used (Desk step 1). No correlation try found anywhere between alter out of increase or BnNrt2 transcript account and supply amino acid levels otherwise proportion among them.
- Viewpoints revealed certainly are the technique of Milwaukee hookup apps three separate replicates ± SD of suggest.
Relationship between glutamine when you look at the phloem latex and you will nitrate uptake through the N-deprivation and over the development years
It is well established that N-deprivation leads to a transient ‘de-repression’ of high-affinity nitrate influx and Nrt2 gene expression in plants with a low N status ( Lejay et al. 1999 ; Forde 2002 ). In plants with a high N status, ‘de-repression’ seems to be bypassed, leading to a direct decline of nitrate uptake interpreted as ‘de-induction’ ( Clarkson 1986 ; Siddiqi et al. 1989 ; Faure-Rabasse et al. 2002 ). Our results for 15 NO3 – influx and BnNrt2 gene expression (Fig. 1a & c) are consistent with these previous studies.