Immunocytochemical Localization of Hydroxyproline-Rich Glycoproteins Accumulating in Melon and Bean at Sites of Resistance to Bacteria and Fungi. R. J. O’Connell. Department of Agricultural Sciences, University of Bristol, Agricultural and Food Research Council Institute of Arable Crops Research, Long Ashton Research Station, Bristol, BS18 9AF, U.K.. I. R. Brown(2), J. W. Mansfield(2), J. A. Bailey(1), D. Mazau(3), D. Rumeau(3), and M.-T. Esquerré-Tugayé(3). (1)Department of Agricultural Sciences, University of Bristol, Agricultural and Food Research Council Institute of Arable Crops Research, Long Ashton Research Station, Bristol, BS18 9AF, U.K.; (2) Biochemistry and Biological Sciences Department, Wye College, Ashford, Kent, TN25 5AH, U.K.; and (3)Université Paul Sabatier, Centre de Physiologie Végétale, NA 241 CNRS, 31062 Toulouse Cédex, France.. MPMI 3:33-40. Accepted 15 September 1989. Copyright 1990 The American Phytopathological Society.

Immunocytochemistry was used to locate hydroxyproline-rich glycoproteins (HRGPs) during incompatible interactions in hypocotyls of Phaseolus vulgaris inoculated with Colletotrichum lindemuthianum, and in leaves of Phaseolus vulgaris and Cucumis melo inoculated with Pseudomonas syringae pv. phaseolicola or with P. fluorescens (a saprophyte). Postembedding immunogold labeling with antibodies to melon HRGP_2b showed that HRGPs accumulated in walls of living plant cells adjoining dead hypersensitive cells during resistant reactions to both the fungus and bacteria. HRGPs were also detected in papillae encasing intracellular fungal hyphae and in small papillae adjacent to bacterial colonies. Intercellular material encapsulating cells of P. fluorescens also contained HRGPs. The highly localized accumulation of HRGPs at sites where the growth of bacteria and fungi is arrested supports the involvement of these structural glycoproteins in disease resistance.