MITOSIS AND CELL DIVISION IN HYDRURUS FOETIDUS (CHRYSOPHYCEAE)¹

Abstract

Mitosis and cell division have been examined ultrastructurally in the vegetative cells of Hydrurus foetidus (Vill) Trev. and found to resemble that of Ochromonas in two important aspects. First, the rhizoplast acts as the spindle organizing body and second, the spindle elongates considerably during anaphase. It differs from Ochromonas in that there is no movement of the basal bodies and flagella towards the poles. Moreover, the nuclear envelope remains relatively intact throughout early stages of mitosis, with gaps developing at the poles during prophase to permit entry of spindle microtubules. Disruption of the nuclear envelope does not occur in the equatorial plane until late anaphase. The spindle persists into telophase and is bent towards the posterior of the cell by the ingrowing edge of the cleavage furrow. Persistence of the spindle and lack of Ochromoms‐type cell elongation may be related to the constricting presence of the sheath during cell division—a completely different strategy to that adopted by the green algae under conditions of similar constraint.

Biology and systematics of heterokont and haptophyte algae

“…Spindle microtubules attach to either basal bodies (diatoms) or the striated flagellar roots (Chrysophyceae). However, in Hydrurus (Chrysophyceae), the nuclear envelope remains largely intact, with openings at the poles (Vesk et al, 1984). Pelagococcus (Pelagophyceae; Vesk and Jeffrey, 1987), Synura (Synurophyceae; Andersen, 1989), and most Phaeophyceae (see Green, 1989, for references) behave similarly to Hydrurus.…”

Septum Formation in the Green Alga Ulothrix Palusalsa (Chlorophyta, Ulvophyceae)

“…This phenomenon has not been described earlier, although published micrographs of septum formation in the green algae Scenedesmus (NILSHAMMER & WALLES 1974), Closterium (PICKETT-HEAPS & FOWKE 1970) and the chrysophycean alga Hydrurus (VESK et al 1984) might be interpreted this way. Despite the observed association of MVB-like profiles with the folding flattened parts of the forming septum in U. palusalsa it is not clear whether Figs.…”

The 18S and 28S rDNA identity and phylogeny of the common lotic chrysophyteHydrurus foetidus

“…This is known also from other chrysophytes (Raikov, 1994). The bases of two vestigial flagella on the vegetative cell of Hydrurus were first shown by Vesk et al (1984) and in more detail by Hoffman et al (1986;see also Andersen, 1991) -gained by a very laborious (and expensive) method only available in dedicated laboratories. We are confronted with the fact that molecular methods are the most efficient tools for evaluation of evolutionary relationships, across diverging morphologies, incommensurable information, and different environments.…”

“…A problem with the morphological evidence at the transmission electron microscopy level is the uneven availability of information concerning characters of possible evolutionary significance, like mitosis, meiosis, cytoskeletal construction and function, and the ultrastructure of the flagellar bases. Mitosis in Hydrurus has been investigated by electron microscopy (Vesk et al, 1984) and exhibits a variant of orthomitosis (Raikov, 1994), involving a symmetrical metaphase within the boundaries of a more or less deconstructed nuclear membrane. This is known also from other chrysophytes (Raikov, 1994).…”

“…Klebs, 1893, Mack, 1953Fukushima, 1962;Joyon, 1963;Klaveness & Lindstrøm, 2011) and electron microscopy (e.g. Hovasse & Joyon, 1960;Vesk et al, 1984;Hoffman et al, 1986;Andersen, 1991), and the details of its peculiar silicified stomatocyst have been outlined (Hovasse & Joyon, 1960). The motile zoospores have attracted attention, since their tetrahedral shape appears to be unique to Hydrurus and genera identified as related, partly due to the morphology of motile cells (e.g.…”