The organization of microtubular systems in the quadriflagellate unicell Polytomella agilis has been reconstructed by electron microscopy of serial sections, and the overall arrangement confirmed by immunofluorescent staining using antiserum directed against chick brain tubulin. The basal bodies of the four flagella are shown to be linked in two pairs by short fibers. Light microscopy of swimming cells indicates that the flagella beat in two synchronous pairs, with each pair exhibiting a breast stroke-like motion. Two structurally distinct flagellar rootlets, one consisting of four microtubules in a 3 over 1 pattern and the other of a striated fiber over two microtubules, terminate between adjacent basal bodies. These rootlets diverge from the basal body region and extend toward the cell posterior, passing just beneath the plasma membrane. Near the anterior part of the cell, all eight rootlets serve as attachment sites for large numbers of cytoplasmic microtubules which occur in a single row around the circumference of the cell and closely parallel the cell shape. It is suggested that the flagellar rootlets may function in controlling the patterning and the direction of cytoplasmic microtubule assembly. The occurrence of similar rootlet structures in other flagellates is briefly reviewed.The presence of flagellar rootlets, constructed of microtubules in a characteristic grouping and/or striated fibers, originating near flagellar basal bodies, is a common feature of motile algal cells. In some of these algae, for example, Chlamydomonas (34) and the zoospores of Microthamnion (43), the microtubules comprising the flagellar rootlets appear to constitute the entire cytoplasmic microtubule system. In others, Ochromonas (2) and the zoospores of Schizomeris (1), large numbers of additional cytoplasmic microtubules appear to attach to the flageUar rootlets. In an earlier series of papers (2, 4, 5) it was shown that in the formation of this attachment in Ochromonas the flagellar rootlets, the rhizoplast and kineto-beak fiber in this organism function as nucleating sites (or microtubule-organizing centers, 29) for the initial assembly of cytoplasmic microtubules. These observations were made on cells in which the cytoplasmic microtubule system was regenerating after an exposure to hydrostatic pressure or antimitotic chemicals. To further clarify this proposed function, we suggested that it was important to examine the role of such sites during the normal development of the cytoplasmic microtubule system (e.g. in synchronously dividing cultures), and ultimately to analyze the polymerization capabilities of these structures in an in vitro 106

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The effects of brief exposure to, or growth in the presence of, lethal and sublethal concentrations of Cu(NO)2 and Cd(NO3) on the ultrastructure of the blue-green algaAnabaena 7120 and the green algaAnkistrodesmus braunii were studied. Exposure to increasing amount of both metal ions led to the appearance of larger proportions of electron-dense cells whose organelles were less well defined than those of untreated cells. Metal-treated cells ofAnabaena 7120 became distorted. Some had a corrugated appearance. Others lysed, leaving a much larger proportion of heterocysts. Such heterocysts were often empty or had a curious collapsed appearance. Growth ofA. braunii in the presence of 10(-4) M Cu(NO2)2 produced substantial numbers of multinucleate giant cells with thick walls; such cells result from repeated mitotic division without subsequent cytokinesis. The giant cells contained centrioles, structures not as yet found in normal cells of the genusAnkistrodesmus. Some nuclei of giant, but not of normal, cells contained deep indentations that appeared as "holes" in cross section. Some giant cells also contained triple parallel strands of endoplasmic reticulum which extended across much of the cell, connecting to the nuclear envelope. Some ultrastructural changes were also noted in algal cells grown over sediment containing Cu or Cd, but these were generally less severe than those occurring when metal ions were added directly to the algal cultures.

The caves are the biodiversity centers for different types of microorganisms, especially for cyanobacteria. They are also present in almost all extreme environments, and their importance in terrestrial ecosystems is greater because of the decreased competition from vascular plants. Cyanobacteria occurring on rocks are epilithic (colonizing the substrate surface), hypolithic (growing under pebbles and small stones), and endolithic (present in an upper layer of rock). There are three limiting factors for cyanobacteria growing in caves: light or its lack, high humidity, and constant temperature. In caves, one can find not only the cosmopolitan cavernicolous species but also rare taxa. Light, transmission, and scanning electron microscopy (SEM), laboratory cultures, as well as molecular phylogenetic studies are important tools in the study of cave cyanobacteria.