Investigation of Nitrate uptake via nitrate transporter (iHATS) in transgenic tobacco (Nicotiana plumbaginifolia) line B-11

Nitrate influx across the plasma membrane by NO3- transport systems named LATS and HATS. Low affinity transport systems (LATS) act at high levels of external NO3- (in mM level) but high affinity transport systems (HATS) act at low levels of external NO3- (in M level). The members of the NRT2 gene family encode inducible high affinity nitrate transporters (iHATS) that among them NRT2.1 and NRT2.2 genes both are involved in nitrate uptake. It seems the role of NRT2.1 gene is more important than the other one. The activity of both genes also need the expression of another gene that so called NAR2. Therefore, in order to gain further insight into the mechanisms of nitrate uptake by inducible high affinity transport systems, the transgenic Nicotiana plumbaginifolia which was transformed by AtNRT2.1 and NAR2 genes (were isolated from Arabidopsis thaliana) together with kanomycine resistance marker gene was used. The rate of nitrate uptake in the medium containing different concentration of nitrate (10, 25, 50, 75 and 100 M) was studied in wild type and transgenic plants at hydroponic condition. The results revealed that almost in all different concentration of nitrate in the medium, wild type plant absorbed the nitrate with 2 to 3 hours delay. Whereas transgenic plants started to uptake the nitrate immediately. On the other hand the rate of nitrate uptake in transgenic plants was much higher than wild type plants at 10 and 25 M concentrations nitrate in the medium. By increase of nitrate concentration in the medium (from 50 to 100M) no significant difference in uptake in transgenic and wild type plants was observed. Furthermore, the results also showed that when the transgenic and wild type plant were grown in 50M nitrate in the medium in hydroponic condition, no significant difference on growth factors (root and shoot length, fresh weight and relative chlorophyll) was observed.