Abstract: The third untreated leaf was challenge inoculated with Xanthomonas oryzae pv. oryzae 3 d after rice seedlings (except the third leaf) pre treated with 0.5 mmol/L and 2.0 mmol/L salicylic acid (SA) solution. The lesion lengths of the third leaf in the two treatments were reduced by 10.2% and 18.2% than those in the CK respectively two weeks after inoculation. It indicated that SA had induced systemic resistance to bacterial blight in rice seedlings. Determination of enzyme activities showed catalase (CAT), ascorbate peroxidase (APX) activities declined significantly in untreated leaves, while no significant changes in peroxidase (POD) activity. It was also observed that there was a difference of effect on superoxide dismutase (SOD) activity between 0.5 mmol/L and 2.0 mmol/L SA. No significant changes of SOD activity were showed in treatment with 0 5 mmol/L SA, however, that in treatment with 2.0 mmol/L SA increased relatively significantly. The H₂O₂ content increased by 23.6%-72.8% and 31.2%-122.6% respectively in the third leaf when rice seedlings were treated with 0.5 mmol/L or 2.0 mmol/L SA within 1-4 d. Therefore, the significant increase in H₂O₂ content may be due to both the enhancement of production and the decline in degradation (2.0 mmol/L SA), or to the decline in degradation only (0.5 mmol/L SA). It was also showed that SA could enhanced phenylalanine ammonia lyase (PAL) activity 3 d following treatment. The results indicated that accumulation of H₂O₂ and increase in PAL activity might involve in the systemic resistance to bacterial blight induced by SA in rice seedlings.

Key words: salicylic acid, rice, bacterial blight, systemic resistance, enzyme activities, peroxide hydrogen

摘要： 0.5、2.0 mmol/L 的水杨酸（SA）处理水稻幼苗后第3 天用稻白叶枯菌（Xanthomonas oryzae pv. oryzae）对未处理叶（第3叶，进行SA处理时用塑料袋套住）挑战接种，2周后调查病情，发现病斑长比对照分别下降了10.2%和18.2%，说明SA能诱导水稻幼苗对白叶枯病的系统抗性。酶活性测定表明，两种浓度的SA能明显降低水稻幼苗未处理叶中过氧化氢酶（CAT）和抗坏血酸过氧化物酶（APX）的活性，而对过氧化物酶（POD）活性无明显影响。两种浓度的SA对未处理叶中超氧化物歧化酶（SOD）活性的影响不同，其中0.5 mmol/L 的SA处理下，SOD无明显变化，但20 mmol/L 的SA对SOD活性有较明显的促进作用。SA处理后1～4 d，未处理叶H2O2含量比对照上升了23.6%～72.8％(0.5 mmol/L)和31.2%～122.6％(2.0 mmol/L)。H2O2水平的显著提高可能是H2O2产生加快和降解减慢的共同结果（2.0 mmol/L的SA下），或单纯的降解减慢所致（0.5 mmol/L的SA下）。同时，SA对未处理叶PAL活性有促进作用。提示在水稻中，SA对水稻抗白叶枯病的系统诱导作用可能与H2O2积累和PAL活性的升高有关。

关键词: 水杨酸, 水稻, 白叶枯病, 系统抗性, 酶活性, 过氧化氢