Role Of Nitrate Reductase In The Regulation Effects Of Sulfur Dioxide On The Physiological Process In Arabidopsis Under Drought Stress

Sulfur dioxide?SO₂?is a common air pollutant,its toxic mechanisms were widely studied in the past.However,recently studies have shown that SO₂ was involed in plants response to pathogen infection,cadmium and aluminum stress.Effects of SO₂ pre-treatment on plant morphology,redox system,osmotic adjustment substances and gene expression under drought stress were investigated in wild type and mutant nia1nia2?for nitrate reductase[NR]-defective double mutant?Arabidopsis.Role of nitric reductase-dependent nitric oxide production in the regulation effects of SO₂ on drought adaptability was also investigated.We achieved the following results:1.SO₂ pre-treatment could improve drought adaptability through regulating the physiological indexes in Arabidopsis under drought stress.?1?In wild type and mutant nia1nia2 Arabidopsis,leaf relative water content?LRWC?decreased and leaf wilting increased with increasing drought stress and extension of time for drought stress;SO₂ pre-treatment alleviated leaf wilting and maintained higher relative water content under drought conditions.However,effects of SO₂ pre-treatment on drought adaptability were different between wild type and mutant nia1nia2 Arabidopsis.Drought stress induced high levels of hydrogen peroxide?H2O2?and malondialdehyde?MDA?,increased the activities of superoxide dismutase?SOD?,peroxidase?POD?,glutathione peroxidase?GPX?and glutathione S-transferase?GST?and the content of glutathione?GSH?in wild type and mutant nia1nia2 Arabidopsis;While SO₂ pre-treatment further increased the activities of SOD,POD,GPX,the content of glutathione of GSH and decreased the contents of H2O2 and MDA under drought conditions;Compared with mutant nia1nia2,effects of SO₂ pre-treatment on the physiological indexes above in wild type Arabidopsis under drought stress were stronger.The results suggested that SO₂ pre-treatment could alleviatethe oxidative stress in Arabidopsis plants by increasing antioxidant capacity,and nitrate reductase was involved in regulatory effects of SO₂ on redox system in Arabidopsis under drought stress.In wild type and mutant nia1nia2 Arabidopsis,the contents of proline and soluble sugar significantly increased with increasing drought stress and extension of time for drought stress;SO₂ pre-treatment further increased the contents of proline in wild type Arabidopsis under drought conditions,while the effect of SO₂ on proline content in mutant Arabidopsis under drought stress was slighter than wild type;SO₂ pre-treatment further increased the contents of soluble sugar in wild type and mutant nia1nia2 Arabidopsis under drought conditions and the increase was very similar.The results suggested that SO₂ pre-treatment could promote the accumulation of osmotic adjustment substances,and nitrate reductase was involved in this progress.2.SO₂ pre-treatment could improve drought adaptability through by regulating the expression of related genes in Arabidopsis under drought stress.?1?In wild type and mutant nia1nia2 Arabidopsis,DREB2 A,DREB2B,CBF4 and RD29 A genes were all up-regulated in response to drought stress;SO₂ pre-treatment could significantly increased the expression of the above four genes in wild type Arabidopsis and SO₂ further increased the expression of DREB2 A,DREB2B,RD29 A in wild type under drought stress;SO₂ pre-treatment could significantly increased the expression of DREB2 A,RD29A in mutant nia1nia2 Arabidopsis,while SO₂ further increased the expression of DREB2 B in mutant under the fifth day of drought and the increase was less than wild type.The results suggested that SO₂pre-treatment could upregulate drought-responsive genes,and nitrate reductase was involved this progress.?2?In wild type and mutant nia1nia2 Arabidopsis,MIR398 a was down-regulated and its tagart genes were up-regulated in response todrought stress;SO₂ pre-treatment decreased the expression of MIR398 a in two kinds of Arabidopsis;SO₂ could further down-regulate MIR398 a and up-regulate CSD1 and CSD2 in wild type under drought stress,while effects of SO₂ on the expression of MIR398 a and CSD2 was not significant.The results suggested that nitrate reductase was involved in regulatory effects of SO₂ on mi R398 a and its tagart genes in Arabidopsis under drought stress.3.In wild type and mutant nia1nia2 Arabidopsis,effect of SO₂pre-treatment on NOS activity under drought was similar.The level of NO was lower in mutant after SO₂ pre-treatment under drought stress.SO₂pre-treatment followed by exogenous NO treatment could further enhance the drought adaptability of two kinds of Arabidopsis.Our results suggested that SO₂ pre-treatment could improve drought adaptation of two kinds Arabidopsis by increasing antioxidant capacity,promoting the accumulation of osmotic adjustment substances,regulating the expression of related genes,alleviating the oxidative stress in different extent under drought stress.Nitric reductase-dependent nitric oxide production may be involed in the regulatory effects of SO₂ on drought adaptability.