Cytochemical demonstration of alkaline phosphatase in the contractile vacuole of Dictyostelium discoideum

The cytochemical demonstration of alkaline phosphatase in growing cells of Dictyostelium discoideum revealed the presence of this enzyme in the contractile vacuole. No reaction product was found along the plasma membrane or in the digestive vacuoles. This cytochemical reaction is observed in large contractile vacuoles only and never in the small satellite vacuoles surrounding the main vacuole; however, these small vacuoles seem to belong to the contractile vacuole complex because their membrane exhibits the same faint reaction to polysaccharide stains as do the large vacuoles. The absence of alkaline phosphatase demonstration in small vacuoles may be due to the fact that the two types of vacuoles have different functions.