CALLOSE SYNTHESIS IN SPIROSTANOL TREATED CARROT CELLS IS NOT TRIGGERED BY CYTOSOLIC CALCIUM, CYTOSOLIC PH OR MEMBRANE-POTENTIAL CHANGES

Carrot (Daucus carota L.) cell suspensions were treated with a spirost anol saponin from Yucca. This saponin is an elicitor of callose synthe sis. Irrespectively of the mode of action of spirostanol on the callos e synthase activity itself, the spirostanol-induced callose synthesis in carrot is not preceded by changes in membrane potential, cytosolic free calcium or cytosolic pH. The inability of modulators of cytosolic free calcium content (verapamil, nifedipine and Br-A23187), EGTA and a proton pump inhibitor (vanadate) to inhibit or induce callose format ion is consistent with a calcium- and pH-independent mechanism for cal lose deposition.