硝酸还原酶介导的NO合成参与SO2引发的拟南芥气孔运动的调节

以拟南芥为材料,研究了硝酸还原酶(NR)途径在植物适应SO2胁迫中的作用.结果表明:SO2胁迫可诱导4周龄拟南芥植株叶片NR活性增强、一氧化氮(NO)水平提高,NR活性和NO水平与SO2暴露时间呈正相关.NR抑制剂叠氮化钠(NaN3)可缓解SO2诱发的NO水平升高.RT-PCR检测发现,SO2熏气72 h时拟南芥NR途径关键基因Nia1、Nia2和NiR1均转录上调.研究还发现,SO2可诱发拟南芥野生型、突变体nia2、nia1nia2的气孔关闭,NaN3和NO清除剂c-PTIO可阻止SO2诱发的野生型和nia2气孔关闭,说明通过NR途径合成的NO参与了SO2胁迫诱发的拟南芥气孔运动调节.研究结果表明,NR活性的增强介导了SO2胁迫期间拟南芥叶片NO水平的升高,后者参与胁迫期间拟南芥气孔运动的调控,以增强拟南芥植株对SO2胁迫的适应性.

Stomatal movement regulation by nitrate reductase-dependent nitric oxide production in Arabidopsis response to sulfur dioxide

The crucial role played by nitrate reductase (NR) in Arabidopsis plants in response to sulfur dioxide (SO₂) was investigated. The present results showed that NR activity in four-week-old Arabidopsis plants increased gradually during 72 h of SO₂ exposure. Meanwhile nitric oxide (NO) level in leaf guard cells increased in a time-dependent manner during 24 h of SO₂ exposure. The NR activity and NO levels showed a positive correlation in Arabdopsis plants in response to SO₂ stress. The increase of NO level induced by SO₂ was efficiently blocked by nitrate reductase inhibitor sodium azide. The results of RT-PCR analysis showed that Nia1, Nia2 and NiR1 genes, which encode the key components of the nitrate reductase pathway, were all up-regulated in Arabidopsis shoots after Arabidopsis plants fumigated with 30 mg · m^-3 SO₂ for 72 h. These results demonstrated an enhanced nitrate reductase-dependent NO synthesis in response to SO₂ stress. By studying stomatal movements, which are well recognized as a model system for studies on cellular signal transduction pathway, we provided clear evidences for the involvement of nitrate reductase-dependent NO production in stomatal movement regulation upon SO₂ exposure. Our results showed that SO₂ exposure caused stomatal closure in Arabidopsis wildtype, nia2 and nia1nia2 mutants, however NO scavenger c-PTIO and nitrate reductase inhibitor NaN₃ blocked SO₂-induced stomatal closure in wildtype and nia2 mutant, but can not block SO₂-induced stomatal closure in nia1nia2 mutant. Our results suggested that SO₂ exposure could cause Nia1, Nia2 and NiR1 gene expression, leading to the activation of nitrate reductase pathway in Arabidopsis plants. The enhancement of nitrate reductase pathway generated more NO molecule in plant cells, and then NO was involved in the regulation of stomatal movement in order to protect plants from SO₂ damage.