Induced net Ca 2+ uptake and callose biosynthesis in suspension-cultured plant cells

In suspension-cultured cells of Glycine max and Catharanthus roseus, marked callose synthesis can be induced by digitonin and chitosan. Leakage of a limited pool of electrolytes precedes callose formation, K+ representing the major cation lost. Poly-L-ornithine, as well as the ionophores A 23187 and ionomycin, also induces some callose synthesis but to a lesser extent. Digitonin increases the net uptake of Ca2+ from the external buffer with a time course parallel to callose synthesis but lagging behind the leakage of K+. Nifedipine partly blocks callose synthesis as well as the digitonin-induced increase in net Ca2+ uptake. Taken together, the data support the hypothesis that addition of the various substances might indirectly lead to membrane perturbation causing the common event of an increase in net Ca2+ uptake which results in callose deposition by a direct activation of the Ca2+-dependent and plasma-membrane-located 1,3-β-glucan synthase.