| Recessive mlo resistance allelc of the Mlo locus in barley confers a broad-spectrum resistance to almost all known isolates of powdery mildew pathogen. The mutant can form cell wall apposition at penetration stage resulting effectively resistance to the primary infection. This is apart from the rapid hypersensitive cell death response associated with gene-for-gene resistance.Many cytological researches suggested metabolism state of mesophyll, Ca2+ signal, and other factors involved in resistance to powdery mildew; recent investigation showed that MLO was calmodulin binding protein (CaMBP). But up to now, how these related process interact with each other in cytology level remained unknown. Thus in this study the spatio-temporal expression partterns of MLO protein, CaM, Rubisco and RCA were investigated systemically by molecular cytological methods to better understand the resistant mechanism. Moreover, the dose of expression was quantitatively assayed. The main results gained in this paper were as followed:1. Immuno-cytochemical localization in barley revealed that the MLO protein was specifically expressed in the chloroplast and nucleus at low abundance. Two peaks were seen in MLO protein accumulation 12 h and 48 h after inoculation, respectively, which was the critical period to pathogen infection and development. This suggested that the metabolism state of mesophyll had changed. The enhanced expression of Mlo gene facilitated to suppress the death of mesophyll and to supply plenty of nutrition to the pathogen.2. There was, however, no MLO protein to be detected specifically in epidermal cells. But the gold particles were found binding in the barley-pathogen interface, the extrahaustoria matrix, and all the pathogen organs. The binding sites may be MLO protein or its derivates. It was presumed that MLO protein was originally synthesized by barley epidermal cells, and then was absorbed by the fungal haustoria and transported to hyphae and conidia, and most of the protein accumulated ultimately in cytoplast and cell wall of pathogen. We propose that the MLO protein or its derivate may be a host factor, which was necessary for further development of pathogen.3. CaM is Ca2+ binding protein, which extensively distributed in various plant cells and organelles. Cytochemical localization here showed that it existed in all organclles and cytoplasm, apart from vacuole. CaM in chloroplast of susceptible cultivar increased at 12 h and 48 h after inoculation, but generally, the contents remained relatively stable. This suggested that CaM transfer Ca2+ signal by its changes of topological structures after interact with Ca2+, not by dose effect of the protein. The relative content of CaM in the nucleus of companion cell was the highest in all the cells, and its increase was also most evident after inoculation. The companion cells take part in transport of organic nutrition, indicated the nutrition in the susceptible barley re-distributed after inoculation.2003-5-214. Ultrastructure observation released that the senescence of chloroplast was expedited after inoculation, but its regeneration in the mesophyll cell adjacent to the attacked epidermis was found in the susceptible barley, which in fact delayed the senescence and death of the mesophyll cells. Cytochemical examines showed that the contents of Rubisco and RCA changed rapidly at 12 h after inoculation. The contents in the susceptible cultivar, Ingrid, decreased rapidly, but that in the resistance cultivar, m/o-3, however, increased. Subsequently, the contents of Rubisco and RCA decreased gradually both in Ingrid and /n/o-3, and the contents in Ingrid always kept higher than that in mlo-3. These results suggested that haustoria induced the regeneration of chloroplast of mesophyll cells, and delayed the senescence and death of mesophyll cells; the regeneration of chloroplasts supplied more nutrition to the development of pathogen.
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