The phytohemagglutinin concanavalin A inhibited zygote formation of Chlamydomonas reinhardii. 15-50 tJ-g lectin/ml not only interfered with the mating reaction, but also with cell wall lysis of gametes and zoospores in a crude autolysin preparation gained from copulating gametes. Further, the structure of cell walls shed into the medium after autolysis in the course of the mating reaction and after lysis "from without" in the crude autolysin preparation was stabilized by Con A. Therefore, it must be assumed that the lectin inhibited zygote formation of C. reinhardii by interfering with autolysis of the cell walls of the gametes.
Though Con A inhibited the lytic processes of C.reinhardii, an activation of the autolytic system in @ gametes by the lectin was found to compete with its inhibitory reaction. Con A induced autolysis of @ gametes was dependent on adherence of the cells by their flagella to the surface of the culture vessel or the liquid medium and did not occur in cultures stirred by rotation.
The interferences of Con A with the autolytic system of C. reinhardii were inhibited by methyl-c~-D-mannopyranoside and to a lesser degree by glucose, indicating that the carbohydrate binding sites of the lectin were involved in its reactions with the cells.