Changes of the cell surface charge of amphibian ectoderm after induction.

Isolated ectoderm of early gastrula stages ofTriturus alpestris was treated with vegetalizing factor for 24 h employing the sandwich method (induced ectoderm). Controls were incubated for the same period with γ-globulin which has no inducing activity. Explants of both series were labelled with cationized ferritin, which binds to negatively charged groups at physiological pH. In non-induced ectoderm, ferritin particles can be found as a thin layer all over the plasma membranes. In induced ectoderm the total amount of ferritin bound to the plasma membrane is much lower than in non-induced ectoderm. Ferritin is located in restricted areas only. In contrast to the controls, other membrane areas are free of ferritin particles. The correlation between these results and the change of cell affinity after induction with vegetalizing factor is discussed.