Surface galactolipids of wheat protoplasts as receptors for soybean agglutinin and their possible relevance to host-parasite interaction.

Soybean agglutinin, a lectin specific for N-acetyl-d-galactosamine and d-galactose, was previously shown to agglutinate wheat leaf protoplasts (Larkin 1978 Plant Physiol 61: 626-629). We investigated the receptors for soybean agglutinin on the plasma membrane of these protoplasts. After treatment of the protoplasts with galactose oxidase, they were no longer agglutinated by the lectin, whereas upon reduction of the galactose oxidase-treated protoplasts with sodium borohydride the susceptibility to agglutination was restored. Analysis of the glycolipids of protoplasts surface labeled by the galactose oxidase-borotritide method, revealed that the radioactivity was mainly present in monogalactosyldiglyceride and digalactosyldiglyceride. The same galactolipids were identified as the only receptors for soybean agglutinin by direct binding of the (125)I-labeled lectin to a thin layer chromatogram of the glycolipids of wheat leaf protoplasts.