An inhibitor of the ATP-dependent endoplasmic reticulum Ca2+-pump affects spindle organization in dividing cells of the angiosperm Triticum turgidum but not in species of gymnosperms and pteridophytes MICHAEL ZACHARIADIS1, HARTMUT QUADER2, BASIL GALATIS1 and PANAGIOTIS APOSTOLAKOS1 1 Department of Botany, Faculty of Biology, University of Athens, Athens 157 84, Greece 2 Institute of General Botany, University of Hamburg, D-22609 Hamburg, Germany   Abstract The effects of the mycotoxin cyclopiazonic acid (CPA) on the organization of the microtubule (Mt) cytoskeleton were investigated in dividing cells of different taxa of higher plants. CPA is a specific inhibitor of endoplasmic reticulum (ER) Ca2+-ATPase, which greatly affects the cytosolic Ca2+ concentration. In the CPA-affected cells of the angiosperm Triticum turgidum the maturation of the Mt preprophase band (PPB) is delayed, while the organization of the prophase spindle is disturbed or inhibited. During metaphase, the organization of the bipolar metaphase spindle and the arrangement of the chromosomes are perturbed. In contrast, in the CPA- affected dividing cells of the gymnosperm Pinus brutia and the pteridophytes Asplenium nidus and Adiantum capillus-veneris, the organization of the Mt cytoskeleton is not detectably disturbed. However, CPA affected the progress of the cell cycle in all the plants studied as well as other Ca2+-dependent processes like cell plate development. These observations suggest that: (a) the ER is involved in establishing cytosolic Ca2+-gradients, which control Mt organization in mitotic cells of the angiosperm but not of the gymnosperm and the pteridophyte species examined and (b) in the spindle poles of P. brutia, A. nidus and A. capillus-veneris, microtubule organizing centres (MTOCs) may function, i.e. they display centrosomal properties.   < back .