木质部次生细胞壁增厚参与疣粒野生稻对黄单胞杆菌水稻变种的抗性

 黄单胞杆菌水稻变种（Xanthomonas oryzae pv.oryzae，Xoo）引起的水稻白叶枯病是一个世界性的严重病害。疣粒野生稻（Oryzae meyeriana）对Xoo具有高度抗性，但其抗性机制仍不清楚。本文以抗病的疣粒野生稻和感病的水稻品种大粒香为材料，研究了Xoo侵染对叶片病斑、叶绿体超微结构、光合系统活性和木质部超微结构的影响。结果表明，多种Xoo生理小种导致的疣粒野生稻叶片病斑长度都明显短于大粒香叶片的病斑长度。Xoo病菌侵染显著破坏了大粒香的叶绿体结构，明显抑制了其光合活性，而疣粒野生稻中的变化要轻得多。通过电镜切片，发现疣粒野生稻叶片导管内存在大量的Xoo病菌，这表明Xoo能够侵染疣粒野生稻且能够在叶片内增殖。病菌的侵染诱导了疣粒野生稻木质部次生细胞壁的增厚，抑制了病菌通过导管纹孔向邻近细胞的进一步侵染，这种反应可能参与了疣粒野生稻对Xoo的抗性。

Xylem Secondary Cell-wall Thickening Involved in Defense Responses of Oryza meyerianato Xanthomonas oryzae pv.oryzae

Bacterial blight caused by Xanthomonas oryzae pv.oryzae (Xoo) is one of the most destructive disease of rice worldwide.The wild rice species Oryzae meyeriana possesses high resistance to Xoo but the resistance mechanism is unknown. In this study, the effects of Xoo on leaf lesion, chloroplast ultrastructure, photosystem activity and xylem ultrastructure were examined in O.meyeriana as well as in a susceptible rice cultivar Dalixiang. After inoculation with a variety of Xoo strains, lesion length in the wild rice was much shorter than that in Dalixiang. In the susceptible rice, chloroplast structure was markedly destroyed and photosynthetic activity (gas exchange and chlorophyll fluorescence) was depressed by the pathogen but there were no such effects in O.meyeriana. Electron microscopic observations showed that large numbers of bacteria were present in the xylem vessels of the wild rice, which suggests that Xoo could invade and reproduce in the leaves of O.meyeriana. Xoo infection induced the thickening of xylem secondary cell walls in O.meyeriana, which subsequently inhibited the further invasion of the pathogen into adjacent cells through the vessel pits. This response in the secondary cell wall could be involved in the high resistance of O.meyeriana to Xoo.