CELL-SURFACE INTERACTIONS BETWEEN TOMATO AND CLAVIBACTER-MICHIGANENSE SUBSP MICHIGANENSE - LOCALIZATION OF SOME POLYSACCHARIDES AND HYDROXYPROLINE-RICH GLYCOPROTEINS IN INFECTED HOST LEAF TISSUES

Infection of tomato leaf tissues with Clavibacter michiganense subsp. michiganense is accompanied by marked cell damage and by the formation of fibrillar or granular material at sites where bacterial growth is active. Cells of C. michiganense accumulated abundantly in intercellular spaces at junctions between mesophyll host cells. Using gold-complexed lectins and enzymes, the location of several poly- and mono-saccharides in infected tissues was determined. Host cell wall degradation was associated with an alteration of pectic material. Pectin molecules were found to accumulate at specific sites such as the aggregated chloroplasts in infected cells. The material surrounding invading bacteria contained mainly pectin-like substances and galactose residues whereas cellulosic β-1,4-glucans were restricted to fibrils closely connected to the host cell wall. Since pectin molecules and galactose residues are components of the host cell wall and do not occur at the bacterial cell surface, it is likely that the material accumulating around bacteria is of host origin. In support of this view, hydroxyproline-rich glycoproteins (HRGPs), visualized by means of an antiserum raised against intact or deglycosylated melon HRGPs, were specifically associated with this material. Furthermore, N-acetylgalactosamine residues, found to be one the major compounds of the bacterial cell surface, were absent in the surrounding material. The significance of the accumulation of pectic substances and HRGPs in this material is discussed in relation to disease resistance. © 1991 Academic Press Limited.