二氧化硫暴露对谷子幼苗气孔运动、脯氨酸代谢和抗氧化酶系统的影响

The effect of SO2 exposure on stomatal movement,proline metabolism and antioxidant enzyme system in foxtail millet seedlings

二氧化硫(SO2)是一种有毒的大气污染物,主要经气孔进入植物体内.目前对于SO2毒性的研究多集中在氧化损伤方面,关于SO2对植物脯氨酸代谢的影响及相关分子机制的研究还很少.本文以谷子幼苗为材料,研究了不同浓度SO2气体暴露对叶片气孔运动、脯氨酸代谢和抗氧化酶系统的影响.结果显示,10mg·m^-3SO2熏气对谷子幼苗的叶片形态、相对含水量、气孔开度、脯氨酸含量及抗氧化酶活性均无明显影响.30mg·m^-3SO2暴露24~72h后,叶片出现明显的受损症状,相对含水量降低,叶面气孔开度减小;30mg·m^-3SO2熏气导致叶中脯氨酸含量显著增加,脯氨酸脱氢酶(PDH)活性明显升高.同时,长时间的SO2胁迫可诱导SiPDH基因表达上调,而脯氨酸合成相关基因SiP5CS、SiP5CR表达受到明显抑制.此外,谷子幼苗暴露于30mg·m^-3SO2时,叶中超氧阴离子(O2^-)产生速率与对照相比显著提高,诱导超氧化物歧化酶(SOD)和过氧化氢酶(CAT)活性增强,从而将过氧化氢(H2O2)含量维持在正常水平.以上结果表明,SO2对谷子的毒性效应具有浓度依赖性.高浓度SO2暴露下,谷子能够通过控制气孔开放、调节脯氨酸代谢和抗氧化酶活性等过程来适应SO2胁迫.

Sulfur dioxide(SO2)is a toxic air pollutant.It enters plants mainly through the stomata.To date,studies on the toxicity of SO2 are mostly focused on the oxidative damage caused by SO2.The influence of SO2 on proline metabolism and the relevant molecular mechanisms are largely unknown.In the present study,we investigated the effects of different concentrations of SO2 on stomatal movement,proline metabolism,and antioxidant enzyme system in the leaves of foxtail millet(Setaria italica L).The results showed that 10 mg·m^-3 SO2 fumigation had no significant effect on leaf morphology,relative water content,stomatal aperture,proline content and antioxidant enzyme activity in foxtail millet seedlings.24~72 h of 30 mg·m^-3 SO2 exposure resulted in obvious damage symptoms in the leaves,as well as decreased relative water content and reduced stomatal apertures.In addition,30 mg·m^-3 SO2 fumigation led to significant increase in proline content and proline dehydrogenase(PDH)activity in the leaves of seedlings.Meanwhile,long term of SO2 stress induced up?regulation of SiPDH transcript,while the expression of proline synthesis-related genes SiP5CS and SiP5CR was significantly inhibited.Moreover,under exposure to 30 mg·m^-3 SO2,markedly higher production rate of superoxide anion(O·2^-)was observed in the leaves of seedlings,as compared with the control,which may enhance the activities of superoxide dismutase(SOD)and catalase(CAT),thus maintaining the content of hydrogen peroxide(H2O2)at a normal level.Together,these results suggested that the toxic effects of SO2 on foxtail millets were concentration-dependent.Foxtail millet plants could adapt to SO2 stress by controlling stomatal opening,regulating proline metabolism and antioxidant enzyme activity when exposed to high concentration of SO2.