WALL APPOSITIONS INDUCED BY IONOPHORE A23187, CACL2, LACL3, AND NIFEDIPINE IN CHARACEAN CELLS

The formation of wall appositions (plugs) by ionophore A 23187, CaCl2, LaCl3, and nifedipine was studied in mature internodal cells of characeaen algae. CaCl2 at concentrations above 10-2M induces thick fibrillar plugs without callose in Nitella flexilis. In Chara corallina and Nitella flexilis ionophore A 23187 (1.25×10-5 to 5×10-5M) and LaCl3 (7.5×10-5 to 2.5×10-4M) cause flat appositions which contain callose and have a more granular structure. Plug formation by ionophore A 23187, CaCl2, and LaCl3 is pH-dependent and occurs beneath the alkaline regions of the cell. Nifedipine (10-4 to 10-5M) induces plugs in Nitella flexilis after previous injury. These callose-containing wall appositions consist of a heterogeneous granular core which is covered by a fibrillar layer. The results of this work are compared with previous studies on wound wall formation and chlortetracycline (CTC)-induced plug formation which reveal that abundant coated vesicles occur only when a thick fibrillar wall layer is formed. Neither LaCl3 nor nifedipine inhibit the formation of CaCl2- or CTC-plugs. The unusual effects of these substances, which normally act as Ca2+ antagonists and therefore should prevent and not induce plug formation, are discussed. It is suggested that La3+ mimicks the effects of calcium and that nifedipine binding to the Ca2+ channels is altered in the alkaline regions of characean internodes and allows an influx of Ca2+. © 1990 Springer-Verlag.