外质体H_2O_2和木质素积累在镍诱导的水稻对白叶枯病系统抗性中的作用

The Role of Apoplastic Hydrogen Peroxide and Lignin Accumulation in the Systemic Resistance of Rice to Bacterial Blight Induced by Nickel

【目的】植物外质体是病原入侵的结构和生理性屏障。本文研究外质体反应在镍诱导的、对白叶枯病系统抗性中的作用,以探讨植物对病原和重金属交叉抗性的生理机制。【方法】以0.5、1.0和2.0mmol·L-1硝酸镍喷施三叶期水稻幼苗的第二叶及以下部位,3d后在未处理的第三叶接种稻白叶枯菌(Xanthomonas oryzae pv.oryzae,Xoo),接种后12d调查病情。测定了2.0mmol·L-1镍处理或/和Xoo接种的幼苗第三叶外质体中愈创木酚POD(G-POD)、NADH-POD、二胺氧化酶(DAO)活性、H2O2和木质素含量。【结果】镍诱导了幼苗对白叶枯病的系统抗性,其中2.0mmol·L-1镍的诱导效果最佳。镍处理下,第三叶外质体液(AWF)中和细胞壁结合的G-POD、NADH-POD,以及AWF中DAO的活性和H2O2水平快速上升,木质素含量显著提高;镍诱导且接种组中,上述指标均明显高于未诱导但接种组。另外,产生H2O2的POD的抑制剂NaN3降低了镍诱导的H2O2积累水平和对白叶枯病的系统诱抗效应,而NADPH氧化酶抑制剂(diphenyleneiodonium chloride)预处理则无明显影响。【结论】本研究结果提示,NADH-POD和DAO活性上升是镍诱导外质体H2O2产生的原因;外质体H2O2和木质素在细胞壁中的积累可能参与了镍诱导的水稻对白叶枯病系统抗性的建立。

[ Objective ] Apoplast in plants acts as the structural and physiological barrier against pathogen attacks. In present paper, the role of apoplastic responses in the systemic resistance of rice seedlings to bacterial blight induced by nickel were investigated so as to explore the physiological mechanisms involved in the cross-resistance to pathogens and heavy metals. [ Method ] The second leaf and its lower parts of three-leaf stage rice seedlings were sprayed with nitrate nickel at 0.5, 1.0 and 2.0 mmol· L^-1. The untreated third leaf was inoculated with Xanthomonas oryzae pv. oryzae （Xoo） 3 d after spraying, and the disease symptoms were evaluated 12 d after inoculation. The activities of apoplastic guaiacol peroxidase （G-POD）, NADH-POD, diamine oxidase （DAO） and the contents of H2O2 and lignin were determined in the third leaves of seedlings treated with 2.0 mmol L^-1 nickel or/and inoculated with Xoo. [Result] The systemic resistance of seedlings to bacterial blight was induced by nickel. The best induction effect occurred at 2.0 mmol· L ^-1 nickel. Nickel not only led to the enhancement in the activities of G-POD and NADH-POD, which are present in apoplastic water fluid （AWF） and are associated with cell wall, but also the enhancement in DAO activity in AWF. Concurrently, a rapid increase in apoplastic H2O2 level and a significant increase in lignin content were also observed in treatment with nickel. On the other hand, the parameters mentioned above in the nickel-induced and Xoo-inoculated seedlings werealways higher than those in the non-induced but Xoo-inoculated ones. Additionally, NaN〉 an inhibitor of PODs mediating in apoplastic H2O2 formation, compromised the H2O2 accumulation and systemic resistance against bacterial blight induced by nickel. However, diphenyleneiodonium chloride, an inhibitor of NADPH oxidase, exerted no effects on them. [Conclusion] The results suggest that the increase in the activities of NADH-POD and DAO contributes to the production of apoplastic H2O2 induced by nickel, and the rapid enhancement in apoplastic H2O2 level and lignin accumulation in cell wall may be involved in the systemic resistance to bacterial blight induced by nickel.