Elevated CO2 differentially regulates root nitrate transporter kinetics in a genotype and nitrate dose-dependent manner

The nitrogen (N) and protein concentration of wheat crop and grain often decline as a result of exposure of the crop to elevated CO2 (EC). In our earlier studies, it was found that the exacerbated production of nitric oxide (NO) represses the transcription of nitrate reductase (NR) and high affinity nitrate transporters (HATS) in EC grown wheat seedlings receiving high N. High N supply under EC also resulted in accumulation of reactive oxygen species (ROS), and reactive nitrogen species (RNS; NO and S-nitrosothiols) ensuing faster senescence and reduced N metabolite concentration in wheat. In this study, the effect of short-term exposure to EC on nitrate uptake kinetics was studied. The impact of EC on constitutive and inducible components of high affinity and low affinity nitrate uptake systems (HATS and LATS) were delineated in two wheat genotypes diverse in terms of nitrate uptake and assimilation capacities. Nitrate dose-response of NR was suppressed by EC in both leaf and root tissues. Plants grown under EC- displayed a marked reduction in nitrate uptake kinetic components of LATS. Wheat genotype with high leaf nitrate assimilation capacity was able to maintain considerably higher nitrate uptake rate under EC albeit at a lower rate in comparison to ambient CO2. Wheat leaves exposed to EC displayed a comparatively higher abundance of NO and showed incremental abundance depending on increase in nitrate supply. Exogenous NO supply significantly suppressed the nitrate uptake rate of EC grown plants. Hence, EC induced production of NO downregulates LATS kinetics in a genotype and nitrate dose-dependent manner.

Automated summary

Exposure of wheat plants to elevated CO2 can lead to a decrease in nitrogen and protein concentration, as well as disrupted nitrate uptake and nitrogen metabolism, due to the exacerbated production of nitric oxide. The study found that external supply of nitric oxide suppressed nitrate uptake in wheat plants under elevated CO2, affecting the kinetics of low affinity nitrate uptake. Different wheat genotypes displayed varying abilities to maintain nitrate uptake under elevated CO2, with high leaf nitrate assimilation capacity being a determining factor. Overall, elevated CO2-induced nitric oxide production downregulated the kinetics of nitrate uptake in a genotype and nitrate dose-dependent manner.