Elevated CO2-induced production of nitric oxide differentially modulates nitrate assimilation and root growth of wheat seedlings in a nitrate dose-dependent manner

Abstract

Wheat is a major staple food crop worldwide contributing approximately 20% of total protein consumed by mankind. The nitrogen and protein concentration of wheat crop and grain often decline as a result of exposure of the crop to elevated CO (EC). The changes in nitrogen (N) assimilation, root system architecture, and nitric oxide (NO)-mediated N signaling and expression of genes involved in N assimilation and high affinity nitrate uptake were examined in response to different nitrate levels and EC in wheat. Activity of enzyme nitrate reductase (NRA) was downregulated under EC both in leaf and root tissues. Plants grown under EC displayed enhanced production of NO and more so when nitrate supply was high. Based on exogenous supply of NO, inhibitors of NO production, and NO scavenger, regulatory role of NO on EC mediated changes in root morphology and NRA was revealed. The enhanced NO production under EC and high N levels negatively regulated the transcript abundance of NR and high affinity nitrate transporters (HATS).

CO2 Elevation Accelerates Phenology and Alters Carbon/Nitrogen Metabolism vis-à-vis ROS Abundance in Bread Wheat

“…Wheat seedlings were raised in hydroponics as described in Adavi and Sathee (2018). Seeds were washed with double distilled water and then surface sterilized with 0.1% mercuric chloride (HgCl 2 ) for 5 min.…”

“…Expression of the following genes: TaNPF1.1, TaNPF2.1, TaNPF2.2, TaNPF2.3, TaNPF2.4, TaNPF6.1, TaNPF6.2, TaNPF6.5, TaNPF6.6, TaNPF7.1, TaGS2 and Ta Fd-GOGAT were studied. The procedure for plant growth and expression profiling was done as described in Adavi and Sathee (2018). qRT-PCR was done using gene specific primers ( Supplementary File 3).…”

“…CO 2 Elevation results in production of NO via nitric oxide synthase (NOS) pathway and regulates the NR activity (Du et al, 2016). Regulation of NR activity by NO is dependent on nitrate availability: low nitrate leads to up-regulation of NR activity whereas; high nitrate leads to downregulation of NR activity (Du et al, 2008;Adavi and Sathee, 2018). Reduced NR activity under CE is due to S-nitrosylation mechanism by NO (Du et al, 2016).…”

“…Recently, Foyer and Noctor (2020) also concluded that apoplastic ROS signals were increased at high CO 2 , and possibly due to the involvement NADPH oxidases ( Cheeseman, 2006 ; Qui et al, 2008 ; Mhamdi and Noctor, 2016 ). Although CE helps in the retention of chlorophyll pigment ( Li et al, 2019 ), it might also lead to production of toxic ROS and RNS (reactive nitrogen species) like nitric oxide (NO) ( Adavi and Sathee, 2018 ; Foyer and Noctor, 2020 ).…”

Present knowledge and controversies, deficiencies, and misconceptions on nitric oxide synthesis, sensing, and signaling in plants

“…Accordingly, NO-treated plants displayed less starch granules and increased sugar content (León, Costa, & Castillo, 2016). Regarding another primary metabolic pathway, nitrate assimilation seems to be also controlled by NO through negative transcriptional regulation on NR and high affinity nitrate transporter encoding genes in wheat (Adavi & Sathee, 2019), a process that seems to be dependent on the N compound source (Balotf et al, 2018). On the other hand, NR-mediated NO generation increases nitrogen uptake capacity by inducing lateral root formation under partial nitrate nutrition in rice (Sun et al, 2015).…”