FEMALE GAMETE MEMBRANE-GLYCOPROTEINS POTENTIALLY INVOLVED IN GAMETE RECOGNITION IN ECTOCARPUS-SILICULOSUS (PHAEOPHYCEAE)

In the plasma membrane-enriched fraction of female gametes of Ectocarp us siliculosus (Phaeophyceae) four sex-specific glycoproteins (P2-3, P 5, P16) exposing N-acetylglucosamine (GlcNAc) residues were detected i n vitro. In immunoblots these proteins were labelled with the GlcNAc c omplementary lectin wheat germ agglutinin (WGA) conjugated to digoxige nin. P2 also cross-reacted with the mannose-specific Galanthus nivalis agglutinin (GNA). Previously, a key and lock mechanism of gamete reco gnition was demonstrated in vivo: fertilization can be selectively inh ibited by a WGA pretreatment of female gametes, or by GlcNAc pretreate d male gametes. Lectins with different carbohydrate requirements such as GNA do not affect fertilization in vivo. Thus, the remaining glycop roteins P3, P5 and P16 seem to be involved in cell-cell recognition du ring fertilization, and possibly one of them functions as the male rec eptor in the plasma membrane of female gametes. Membrane proteins of b oth gamete types showed higher differences than cytosolic proteins or proteins extracted from whole cells when examined by high resolution t wo-dimensional gel electrophoresis.