Ultrastructure ofTessellaria volvocina(Synurophyceae)

Scale formation inTessellaria volvocina(Synurophyceae)

“…The SDV membrane of the immature scale is closely appressed and silica deposition is preceded by fine fibrils, presumably of organic material, which run longitudinally within the SDV. The mature spine-scale is fully silicified Extrusion of mature scales to join the colonial investment has not been observed conclusively but must occur only at the anterior end of the cell since scales are never seen between cells or within the colony (Pipes, Leedale & Tyler, 1991). Prior to extrusion there must therefore be a second migration of fully mature scales from the cell posterior, where silicification was completed, to the anterior of the cell.…”

“…Brugerolle & Bricheux (1984) suggested the involvement of actin microfilaments in maintaining the shape of the SDV during the early stages of morphogenesis and also that of microtubules in the migration of the vesicles along the surface of the chloroplast. Presumably the microtubules involved are the cytoskeletal microtubules originating from flagellar root R~ (see Pipes, Leedale & Tyler, 1991). The SDVs of Tessellaria also appear to be produced by fusion of vesicles from the Golgi apparatus but do not become involved with the chloroplast ER of either chloroplast and therefore do not follow the route within the cell described for Synura.…”

“…A possible reason for this difference between Synura and Tessellaria is the position of the chloroplasts within the cells; those of Synura lie longitudinally while the chloroplasts of Tessellaria are orientated transversely ( Fig. 1; see Pipes, Leedale & Tyler, 1991). Leadbeater (1990) discussed how a row of scales, maturing along the length of the righthand chloroplast from the anterior to posterior, is inserted into the scale case of Synura.…”

“…Cultures were grown in a Grttingen-based medium (Pipes, Leedale & Tyler, 1991) in a temperature-controlled growth room at 20°C on a 16:8 h light-dark cycle. Material was fixed for the TEM in 2% osmium tetroxide and 2"5% glutaraldehyde in 0'1 M phosphate buffer (mixed in a ratio of 1 : 1 immediately prior to addition to the centrifuged pellet of cells).…”

“…Tessellaria volvocina Playfair, tentatively placed within the Synurophyceae on the basis of certain ultrastructural features (Pipes, Leedale & Tyler, 1991), has an unusual arrangement and distribution of its siliceous scales (Tyler et al, 1989). The scales do not surround the individual cells as they do in Synura, rather they form an investment around the colony as a whole.…”