Transcriptional Changes Of Arabidopsis In Response To SO₂ And The Involvement Of NO Regulation

Sulfur dioxide (SO2), one of common air pollutants, has numerous physiological impacts on plants. However, it is unknown that how the plant make mechanisms to adapt to SO2 stress. In our current experiment, we have undertaken a profound analysis on genome-scale transcriptome of Arabidopsis, some physiological indicators and stomatal movement in order to reveal the mechanisms of plants in response to adversity stress.According to results, the Arabidopsis ATH1 GeneChip array contained 22810 probe-sets, among which 2780 transcripts in SO2-treated plants versus control (untreated) were significantly altered, including 1109 up-regulated and 1671 down-regulated transcripts. In this study, these differentially expressed genes involved in sulfur metabolism, ROS generating and scavenging pathways, NO biosynthesis pathways, tolerance and defense mechanisms were investigated. Numerous transcripts involved in SO2 metabolic pathway were significantly altered in response to SO2 stress. Further, transcripts encoding components involved in reactive oxygen species (ROS) generating and scavenging pathways, and NO biosynthesis pathways were also up-regulated. Furthermore, transcripts encoding heat shock proteins, nitrilase, lipid transfer proteins, cytochrome P450 were up-regulated by SO2 exposure. Transcripts involved in hormone signal transduction pathways (e. g. auxin, gibberellin, brassinosteroid and ethylene) were also up-regulated.It is confirmed that NO levels and nitrate reductase (NR) activity in Arabidopsis plants response to SO2 stress were increased. NO levels and NR activity, yet, were significantly decreased after adding NR inhibitor (NaN3). NR activity was increased 2.17 fold in Arabidopsis plants fumigated with SO2 for 72 h. In addition, transcripts encoding three key genes, consisted of Nia1, Nia2 and NiR1, involved in NR pathway were also up-regulated. These results further prove that NR mediates NO levels increased in plant response to SO2 stress.Intracellular hydrogen peroxide and proline contents were significantly increased in Arabidopsis plant by SO2 treatment. However, after adding NaN3, hydrogen peroxide and praline contents were decreased with decreased NO levels. With RT-PCR, transcriptional levels of defense genes including CYP81D1、GSTU24、CAT3、CAD8 were analyzed in Arabidopsis wild type and mutant nia1nia2. Consequently, transcriptional levels of those genes in mutant nia1nia2 were not higher than those in wild type.Stomatal guard cells are used in model experimental system to study signal transduction. In current experiment, effects of SO2 derivatives (a mixture of sodium sulfite and sodium bisulfite,3:1 mmol·L-1) on stomatal movement in Arabidopsis wild type and mutant nia1nia2 were investigated. Arabidopsis plants epidermis stomatal aperture were significantly decreased with the increased SO2 concentration.200 U·mL-1 catalase (CAT),1 mM ascorbic acid (ASA), and 0.1 mM MAPK kinase inhibitor PD98059 relieved stomatal aperture decrease caused by 10μM SO2, indicating that both ROS and MAPK were involved in stomatal movement.0.1 mM Ca2+ channel blocker (LaCl3) and 1 mM Ca+ chelator EGTA relieved stomatal aperture decrease caused by 10μM SO2, suggesting Ca2+ was involved in stomatal movement in Arabidopsis upon 10μM SO2 stress.0.2 mM NO scavenger (c-PTIO) and 25 μM NO synthase inhibitor (L-NAME) relieved stomatal aperture decrease caused by 10μM SO2 in both wild type and mutant nia1nia2 plants. However,0.1 mM sodium tungstate was able to relieve stomatal aperture decrease in wild type plants by SO2, rather than mutant nia1nia2 plants. It is demonstrated that NO is involved in stomatal movement, deriving from both NR and NOS pathways.Taken together, it is commonly acknowledged that the expression of genes involved in SO2 metabolic pathways, ROS generating and scavenging pathways, NO biosynthesis pathways, tolerance and defense mechanisms can be changed at transcriptional level in Arabidopsis response to SO2 stress. Moreover, NO triggered by SO2 stress in Arabidopsis plants regulates stomatal movement and defense genes expression including CYP81D1、 GSTU24、CAT3、CAD8 in order to strengthen plants adaptation to environmental stress.