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

YANG Yong,XIE Li,YAN Cheng-qi,WANG Xu-ming,YU Chu-lang,CHENG Xiao-yue,CHENG Ye,CHEN Jian-ping(State Key Laboratory Breeding Base for Zhejiang Sustainable Pest and Disease Control;Key Laboratory of Plant Protection and Biotechnology,Ministry of Agriculture,China;Zhejiang Provincial Key Laboratory of Plant Virology,Institute of Virology and Biotechnology,Zhejiang Academy of Agricultural Sciences,Hangzhou 310021,China)

cell-wall thickening;ultrastructure;Oryzae meyeriana;Xanthomonas oryzae pv.oryzae;resistance mechanism

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.