Protoplasma (1991) 165:173-188 9Springer-Verlag 1991 Printed in Austria Patterns of cortical and perinuclear microtubule organization in meristematic root cells of Adiantum capillus veneris E. Panteris*, B. Galatis, and P. Apostolakos Institute of General Botany, University of Athens, Athens Received November 26, 1990 Accepted April 24, 1991 Summary. The interphase meristematicroot cells ofAdiantumcapillus venerispossess a welldevelopedcytoskeletonof cortical microtubules (Mts), which disappear at prophase. The preprophase-prophasecells display a well organized preprophase microtubule band (PMB) and a perinuclear Mt system. The observations favour the suggestion that the cell edges included in the PMB cortical zone possess a Mt organizing capacity and thus play an important role in PMB for- mation. The perinuclear Mrs are probably organized on the nuclear surface. The preprophase-prophase nuclei often form protrusions towards the PMB cortical zone and the spindle poles, assuming a conical or rhomboid shape. Mts may be involved in this nuclear shaping. Reinstallation of cortical Mrs in dividing cells begins about the mid- dle of cytokinesis with the reappearance of short Mts on the cell surface. When cytokinesis terminates, numerous Mts line the post- cytokinetic daughter wall. Many of them converge or form clusters in the cytoplasm occupying the junctions of the new and the old walls. In the examinedfern, the cortical Mt arrays seemto be initiated in the cortex of post-cytokinetic root cells. A transitory radial peri- nuclear Mt array, comparable to that found in post-telophase root cells of flowering plants, was not observed in A. capillus veneris. Keywords: Adiantum capillus veneris; Meristematic root cells; Mi- crotubule organization; Immunofluorescence microscopy; Electron microscopy. Introduction The determination of the sites, where the cortical Mt arrays are initiated and/or organized in higher plant cells, has been proven to be difficult. Gunning and his collaborators studied in detail Mt organization in mer- istematic and differentiating root cells of the ferns AzolIa pinnata and A. filiculoides, using electron mi- croscopy (Gunning et al. 1978 b, c; Gunning and Hard- * Correspondence and reprints: Institute of General Botany, Uni- versity of Athens, GR-15784 Athens, Greece, ham 1979; Gunning 1980; Busby and Gunning 1983). They were led to the hypothesis that cortical Mt nu- cleation sites function at cell edges. They defined as nucleation sites cytoplasmic loci where electron dense material is localized, cortical Mts converge and a par- ticular category of vesicles is gathered. Since then, cortical sites in higher plant cells where Mrs might be nucleated and/or organized, have been de- scribed in stomatal cells (Galatis 1980, 1982; Palevitz 1981; Galatis etal. 1983; Busby and Gunning 1984; Galatis etal. 1986; Cleary and Hardham 1989, 1990; Cho and Wick 1989), in differentiating meiospores of mosses (Brown and Lemmon 1988), in protodermal cells of Marchantia paleacea (Apostolakos and Galatis 1985a) and in growing pollen (Heslop-Harrison and Heslop-Harrison 1988). In post-cytokinetic cells of Sphagnum, diffuse Mt organizing zones rather than distinct Mt organizing centres (MTOCs) seem to func- tion along the surfaces of the daughter wall to initiate the cortical Mts (Schnepf 1984; see also Marc etal. 1989a, b; Marc and Palevitz 1990). Wick (1985) and Clayton etal. (1985), studying meri- stematic root cells of Allium cepa with immunoflu- orescence microscopy, made the hypothesis that in post-cytokinetic cells the cortical Mrs originate from perinuclear MTOCs. At a late stage ofcytokinesis and/ or immediately after its completion, a prominent sys- tem of Mrs fan out from the nuclear surface. According to this view, these Mts migrate to cell surface forming the cortical Mt arrays. A similar transition between mitotic-cytokinetic and interphase Mt arrays occurs in root cells of mung bean, pea, carrot, Tradescantia (Wick 1985), Zinnia and Lolium (Cleary and Hardham