SPATIAL AND TEMPORAL REGULATION OF NUCLEATING SITES FOR ARRAYS OF CORTICAL MICROTUBULES IN ROOT-TIP CELLS OF THE WATER FERN AZOLLA PINNATA

  • 1 January 1980
    • journal article
    • research article
    • Vol. 23  (1) , 53-65
Abstract
Root primordia of the water fern A. pinnata were examined by conventional and high voltage EM to extend previous evidence concerning the existence and behavior of nucleating sites (NS) for microtubule arrays in the cortex of plant cells. Putative NS are visible as foci consisting of clusters of microtubules, a population of particles or vesicles and associated dense material. They are concentrated along the edges of the cells but become conspicuous only when cortical arrays are being generated, i.e., at the early postcytokinesis phase when interphase arrays are being reinstated and when pre-prophase bands are forming. Examples of temporal regulation during the cell cycle are documented. The predictable anatomy of the Azolla root allows specified edges of cells to be examined in successive cell cycles. The NS first appear at a newly generated edge (where one of the walls that meet at the edge is derived from a new cell plate) and reappear after cytokinesis at that same edge in later cycles, irrespective of the plane of division, when it is no longer newly formed but 1, 2, or more cell cycles old. All edges of a cell, whether radial, longitudinal or tangential, have the potential to develop NS but a strong element of selectivity appears to be imposed. The possible role of the system of NS in microtubule development and overall morphogenesis in the root is discussed.