中文摘要：

【目的】研究小白菜幼苗对二氧化氮（NO2）急性胁迫的应答及过氧化氢（H2O2）的调节作用。【方法】在自制的熏气箱中对供试植株进行NO2（浓度分别为0.25、0.5、1.0和2.0μl·L^-1）熏蒸24h（10﹕00～次日10﹕00）,测定某些生理生化指标。延长熏气至7d,每天7h（8﹕00～15﹕00）,测定植株的生长速率。为了评价外源H2O2在植株对NO2应答中可能的调节作用,熏气前1d对试验组叶面喷洒10mmol·L^-1H2O2溶液（相当于每棵植株喷洒约1mgH2O2）,对照组喷洒等量蒸馏水。【结果】0.25μl·L^-1NO2促进小白菜生长,而0.5μl·L^-1及以上浓度NO2使植株生长速率和叶绿素含量显著降低,叶片硝酸还原酶（NR）和超氧化物歧化酶（SOD）活性以及丙二醛（MDA）含量增加;1μl·L^-1及以上浓度NO2使老叶片出现坏死,绿色部分的过氧化氢酶（CAT）活性和硝酸盐（NO3^-）含量增加,抗坏血酸（ASA）含量和光合速率下降,但气孔导度不受影响。10mmol·L^-1H2O2预处理显著减轻NO2对植株的不利影响,其中生长速率、ASA和MDA含量等与只通入碳滤空气的对照水平相当,光合速率明显恢复,但NO3^-含量和NR活性没有变化,SOD和CAT活性被进一步诱导,气孔导度降低。【结论】NO2急性胁迫引发了小白菜幼苗氧化胁迫伤害;H2O2预处理提高了小白菜的抗氧化能力,增强了对高浓度NO2的耐受性;NO2熏蒸使小白菜叶片NO3^-含量增加。

英文摘要：

[ Objective ]This paper investigated the responses of B. campestris seedlings to acute level of nitrogen dioxide （NO2） exposure in a plant growth chamber, examined whether pre-treating plants with hydrogen peroxide （H2O2） would alleviate NO2-induced injury and discussed the possible role of H2O2 in the modulation of some physiological and biochemical characteristics of the plants. [Method] Some indices were determined in B. campestris seedlings exposed to different concentrations of NO2 （0.25, 0.5, 1.0 and 2.0 μl.L^-1, respectively） for 24 h under controlled environment. To measure the growth rate, plants were fumigated with different concentrations of NO2 for 7 h per day （8 ： 00-15 ： 00） for 7 days. To analyze the possible role of H2O2 involved in plant responses to NO2 stress, the plant leaves were sprayed with 10 mmol.L^-1 H2O2 aqueous solution （corresponding to approximately 1.0 mg H2O2 per single plant）. As a control treatment, water alone was applied. [Result] Exposure to moderate dose of NO2 （e.g. 0.25 μl.L^-1） has a favorable effect on plants, and the growth was promoted. However, exposure to NO2 at 0.5 μl.L^-1 and above caused reductions in the growth rate and chlorophyll, increases in malondialdehyde （MDA） and superoxide dismutase （SOD） and nitrate reductase （NR） activities. Exposure to 1 μl.L^-1 and above of NO2 resulted in necroses appeared on the older leaves, increased catalase （CAT）, decreased ascorbate （ASA）, significantly accumulated NO3, and impaired photosynthesis, but no detected change in stomatal conductance. The pretreatment with H2O2 resulted in recoveries of the plant growth rate, ASA and MDA contents and photosynthetic rate. More inductions of SOD and CAT activities were observed in H2O2- treated plants. However, H2O2 treatment did not alter the nitrate content and NR activity in plant leaves. H2O2 pretreatment caused a lower rate of stomatal conductance. [ Conclusion ] These data suggest that fumigation with acute levels of NO2 causes