Meetings of the Royal Botanical Society of The Netherlands

Extensins are a class of hydroxyproline-rich glycoproteins, and are one of the best characterized classes of structural cell wall proteins present in a wide variety of plants and algae. Recently our group isolated and characterized pistil-specific genes encoding extensinlike proteins in Nicotiana tabacum (Goldman el al. 1992, Plant Cell, 1041-1051). Some of these genes, identified as class III genes, were highly expressed in stigmas and styles and weakly expressed in ovaries. The class III genes were developmentally regulated and not induced in the vegetative tissues under stress conditions like wounding, pathogenic infection or ethylene treatment. The extensin-like proteins encoded by these genes differed from previously described extensins by a lower copy number of the Ser-Pro4 motif and a lower content of tyrosine residues. These residues in particular are thought to play a role in cell wall architecture. In situ hybridization experiments showed that the class III mRNA is specifically localized in the cells of the transmitting tissue. Indirect immunofluorescence was used for the localization of extensins and/or extensin-like proteins. Using a polyclonal antibody raised against soybean seedcoat extensin (kindly provided by Dr J. Varner), we could show the presence of extensins and/or extensinlike proteins in the intercellular matrix and cell walls of the transmitting tissue. Currently, we are undertaking experiments to overexpress the pMG 15 protein in E. coli to generate specific antibodies.