Nitric Oxide Synthase-Dependent Nitric Oxide Production Is Associated with Salt Tolerance in Arabidopsis

Abstract

Nitric oxide (NO) has emerged as a key molecule involved in many physiological processes in plants. To characterize roles of NO in tolerance of Arabidopsis (Arabidopsis thaliana) to salt stress, effect of NaCl on Arabidopsis wild-type and mutant (Atnoa1) plants with an impaired in vivo NO synthase (NOS) activity and a reduced endogenous NO level was investigated. Atnoa1 mutant plants displayed a greater Na 1 to K 1 ratio in shoots than wild-type plants due to enhanced accumulation of Na 1 and reduced accumulation of K 1 when exposed to NaCl. Germination of Atnoa1 seeds was more sensitive to NaCl than that of wild-type seeds, and wild-type plants exhibited higher survival rates than Atnoa1 plants when grown under salt stress. Atnoa1 plants had higher levels of hydrogen peroxide than wild-type plants under both control and salt stress, suggesting that Atnoa1 is more vulnerable to salt and oxidative stress than wild-type plants. Treatments of wild-type plants with NOS inhibitor and NO scavenger reduced endogenous NO levels and enhanced NaCl-induced increase in Na 1 to K 1 ratio. Exposure of wild-type plants to NaCl inhibited NOS activity and reduced quantity of NOA1 protein, leading to a decrease in endogenous NO levels measured by NO-specific fluorescent probe. Treatment of Atnoa1 plants with NO donor sodium nitroprusside attenuated the NaCl-induced increase in Na 1 to K 1 ratio. Therefore, these findings provide direct evidence to support that disruption of NOSdependent NO production is associated with salt tolerance in Arabidopsis.

Hunting for Plant Nitric Oxide Synthase Provides New Evidence of a Central Role for Plastids in Nitric Oxide Metabolism

“…Consistent with the proposed role of NOS1 in NO synthesis, mutant nos1 plants showed decreased NO accumulation in response to ABA, salicylic acid, salt, and elicitor treatments (Guo et al, 2003;Zeidler et al, 2004;Bright et al, 2006;Zhao et al, 2007a;Zottini et al, 2007). Similarly, a decreased NO burst was observed after elicitation of NOS1-silenced N. benthamiana plants (Asai et al, 2008).…”

“…It remains unclear how altered levels of the NOA1/RIF1 protein in loss-of-function or overexpressing lines of eukaryotic algae, plants, and animals result in concomitant changes in NOS activity and NO accumulation (Guo et al, 2003;He et al, 2004;Zeidler et al, 2004;Zhao et al, 2007a;Parihar et al, 2008;Vardi et al, 2008). As recently suggested (Moreau et al, 2008), the decreased NO production in the noa1/rif1 mutant might result from pleiotropic effects of defective plastids.…”

“…Overexpression of NOS1 in Arabidopsis resulted in higher levels of NOS activity in leaf extracts, whereas a knockout mutant (nos1) displayed lower NOS activity in leaf extracts and reduced NO accumulation in roots (Guo et al, 2003). Different groups have independently confirmed the presence of decreased NOS activity and NO levels in the Arabidopsis nos1 mutant (He et al, 2004;Zeidler et al, 2004;Zhao et al, 2007a) and in Nicotiana benthamiana plants with a silenced NOS1 homolog (Asai et al, 2008). Furthermore, enhanced NO production was recently observed in NOS1-overexpressing diatom cells (Vardi et al, 2008), whereas changes in both NOS activity and NO production correlated with the levels of mammalian NOS1 in human cells (Parihar et al, 2008).…”

Proline and Glycinebetaine Ameliorated NaCl Stress via Scavenging of Hydrogen Peroxide and Methylglyoxal but Not Superoxide or Nitric Oxide in Tobacco Cultured Cells

“…3A and B). 16) On the other hand, NaCl has been found to decrease the NO level by inhibiting NO synthase activity in Arabidopsis mutant (Atnoa1) plants with impaired in vivo NO synthase activity, and in wild-type plants as well, 15) but simultaneous increases in NO and H 2 O 2 in tobacco cells induce apoptosis-like cell death. 20) In BY-2 cells, proline and betaine did not reduce NO production under either short-term or long-term NaCl treatment ( Fig.…”

“…8) Environmental stress, including salinity, induces the production of hydrogen peroxide (H 2 O 2 ), the superoxide radical (O 2 À ), and nitric oxide (NO) in plant cells. 1,[12][13][14][15][16][17][18] Excess production of H 2 O 2 , O 2 À , and NO is toxic to plants, and causes oxidative damage to cellular constituents, leading to cell death. [12][13][14][18][19][20] In plant cells, salinity also leads to the accumulation of methylglyoxal (MG), a cytotoxic compound that can react with and modify other molecules, including DNA and proteins.…”