SOMATIC CELL FLAGELLAR APPARATUSES IN TWO SPECIES OF VOLVOX (CHLOROPHYCEAE)¹

Abstract

The somatic cell flagellar apparatuses of Volvox carteri f. weismannia (Powers) Iyengar and V. rousseletii G. S. West have parallel or nearly parallel basal bodies which are separated at their proximal ends. The four microtubular rootlets alternate between two and four members, and all are associated with a striated microtubular associated component (SMAC) that runs between the basal bodies. In addition, each half of the flagellar apparatus apparently rotates during development and loses the 180° rotational symmetry characteristic of most unicellular chlorophycean motile cells. All of these features appear necessary for efficient motion of a colony composed of numerous radially arranged cells. However, the structural details of the flagellar apparatuses of these two species differ. The distance between flagella is greater in V. rousseletii than in V. carteri. One distal striated fiber and two proximal striated fibers connect the basal bodies in V. carteri, but both types of fibers are absent from V. rousseletii. In the latter species, a striated fiber wraps around each of the basal bodies and attaches to the rootlets and the SMAC. No such fiber is present in V. carteri. Since the similarities in the flagellar apparatuses can be explained as a result of adaptation for efficient colonial motion in organisms with similar colonial morphology, the differences suggest a wider phylogenetic distance than previously believed.

Green Algae and the Origins of Multicellularity in the Plant Kingdom

“…The 12 cells on the edge, however, rotate their basal bodies and flagella to a parallel orientation that cause the colony to rotate in a pinwheel-like fashion as it swims forward (Greuel and Floyd 1985). The basal body reorientation observed in Gonium pe-ripheral cells occurs in all of the motile cells of spheroidal volvocine genera and is crucial for coordinated swimming (Hoops 1984;Ueki et al 2010). Visible signs of organismal polarity are present in other aspects of colony development in larger volvocine genera that appear during inversion, germ-soma differentiation, and asymmetric cell division as described below.…”

Motility in the colonial and multicellular Volvocales: structure, function, and evolution

“…In contrast, in most of the colonial and multicellular algae so far examined, the effective strokes of both flagella beat in very nearly the same direction (Gerisch 1959, Hoops andFloyd 1983, K. Feathers et al unpubl.). Judging from the spatial relationship between the beat envelope and the eyespot in unicellular and colonial forms, this probably represents an alternation of the direction of effective strokes in both flagella of the colonial forms (Hoops andFloyd 1983, Hoops 1993). In the colonial species investigated to date, both flagella beat toward the syn side of the cell (Gerisch 1959, Hoops and Floyd 1983, Hoops 1993 (Fig.…”

Channelrhodopsins ofVolvox carteriAre Photochromic Proteins That Are Specifically Expressed in Somatic Cells under Control of Light, Temperature, and the Sex Inducer

“…cp, Chloroplast; cr, channelrhodopsins; ct, chloroplast thylakoids; eg, eyespot granules; ice, inner chloroplast envelope; oce, outer chloroplast envelope; pm, plasma membrane. distinct anterior-posterior polarity (Hoops, 1984(Hoops, , 1993Kirk, 1998). This polarity is not only expressed by the direction in which it swims (i.e.…”

“…with the anterior pole first) but also by morphological characteristics: (1) the spheroid is somewhat more enlarged along the anteriorposterior axis than along the equatorial axis; (2) the daughter spheroids are localized mainly in the posterior hemisphere; (3) the somatic cells near the anterior pole are somewhat larger and more widely spaced than the cells near the posterior pole; (4) the orientation of the flagellar apparatus of each somatic cell is correlated with its position in the spheroid; (5) the eyespots are larger at the anterior pole; (6) in each somatic cell, the eyespot is localized on the side facing toward the posterior pole; and (7) at the anterior pole, the eyespots are located quite a distance from the flagella, whereas the cells in the posterior region have the eyespots closer to the flagella. All of these differences are probably essential for effective organismal motility and the specific photomovement in Volvox (Hoops, 1984(Hoops, , 1993Kirk, 1998).…”