Valve morphogenesis in the centric diatom Rhizosolenia setigera (Bacillariophyceae, Centrales) and its taxonomic implications
Title:
Valve morphogenesis in the centric diatom Rhizosolenia setigera (Bacillariophyceae, Centrales) and its taxonomic implications
Author:
Van de Meene, Allison ML Pickett-Heaps, Jeremy D.
Appeared in:
European journal of phycology
Paging:
Volume 39 (2004) nr. 1 pages 93-104
Year:
2004-02
Contents:
Valve morphogenesis was followed in normal living cells, during treatment with anti-cytoskeletal drugs, and in cells fixed for electron and immunofluoresence microscopy. The long terminal spine-like extrusion is a tubular labiate process (LP). The new valves and LPs were initiated by mid-cleavage. After cytokinesis, the cytoplasts retracted and the LPs extended while the valves grew back over the cytoplasm. Astonishingly, the growing LP, new valve and the cytoplasm within it invariably rotated smoothly 5 - 8 turns in one direction, paused briefly, and then rotated 5 - 8 turns in the other, each full rotation taking 8 - 12 s. This regularly alternating rotation continued from valve initiation until completion and its significance is unknown. The silica wall, secreted within a silica deposition vesicle (SDV), grew at the tip of the spine (i.e. LP) and back over the daughter cell. During LP morphogenesis, a 'labiate process apparatus' was invariably located over the forming labia at its base. The lumen of the growing LP was empty of organelles save the SDV. A microtubule centre (MC) was located eccentrically on the outer edge of the SDV growing back over the cell. Its microtubules (MTs) fanned out over the SDV. A thin dense layer on the cell membrane encircled the cell immediately adjacent to this growing edge of the SDV. Immunofluoresence staining revealed one, occasionally two, adjacent bands of actin girdling the cell here. Treatment with the anti-MT agent oryzalin stopped cytoplasmic rotation while elongation of a deformed LP continued. The anti-actin drug cytochalasin D reduced rotation to small, irregular jerks back and forth while LP elongation ceased; immunofluorescent staining confirmed that these bands were gone. This peculiar morphogenetic machinery is completely different to that of Proboscia, previously thought to be closely related to Rhizosolenia. The purpose of rotation and the mechanism driving tip growth of the LP remain mysterious.
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