Segregative cell division and the cytoskeleton in two species of the genus Struvea (Cladophorales, Ulvophyceae, Chlorophyta)

Abstract

SUMMARY The detailed segregative cell division (SCD) processes and changes in the arrangement of cortical microtubules and actin filaments were examined in two species of Struvea. SCD was initiated by the appearance of annular constrictions along the lateral side of a mother cell. The constrictions decreased in diameter, became thin, tubular in shape, and pinched the protoplasm of the mother cell into several protoplasmic sections. The protoplasmic sections expanded and developed into daughter cells, which appressed each other, and were arranged in a single row. Lateral branches protruded from the upper parts of the daughter cells. The protoplasm of the lateral branches was divided by secondary SCDs and was distributed amongst the new daughter cells. SCD and lateral branch formation were essential for morphogenesis in Struvea. Cortical microtubules were arranged parallel and longitudinally to the cell axis before SCD. When SCD was initiated, there was considerable undulation of the cortical microtubules and several transverse bundles appeared in the cytoplasmic zone where annular constrictions occurred. A microtubule‐disrupting drug (amiprophos methyl) inhibited SCD. Actin filaments maintained reticulate patterns before and during SCD. These results demonstrated that SCD in Struvea species was quite distinct from that in Dictyosphaeria cavernosa reported previously.

A one-billion-year-old multicellular chlorophyte

“…However, this branching pattern is not unique to Cladophoropsis ; it is also present in other siphonocladaleans, such as Cladophora and Rhizoclonium 30 , 31 . More importantly, although they all can have regular intercalary cell divisions and thus centripetal invagination 32 , 33 , some Cladophoropsis species can occasionally have segregative cell division and usually develop tenacular cells as an attachment structure 33 . However, no Proterocladus specimens show a sign of segregative cell division or tenacular cells ( Supplementary Table 1 ).…”

Brilliantia kiribatiensis, a new genus and species of Cladophorales (Chlorophyta) from the remote coral reefs of the Southern Line Islands, Pacific Ocean

“…In some genera, such as Siphonocladus and Struvea , these cells remain inside the mother cell, expand and form new vegetative branches (Kraft and Wynne 1996, Okuda et al. 2016), while in other taxa, such as Boergesenia and Valonia ventricosa , the segregated cells are released from the degenerated mother cell, settle, and form new thalli (Olsen and West 1988). In Brilliantia , the new cells remain in the parent cell, but do not form new lateral branches as in Struvea .…”

pH-Dependent Maintenance of Cell Wall Integrity in the Giant-Celled Green Alga <i>Valonia utricularis</i>

“…In the giant-celled algae, on the other hand, cell walls have been removed by manual dissection under a dissecting microscope (Okuda et al 2016). It has been empirically known by laboratory workers that the cell wall fragments removed from the cell of giant-celled green algae such as Dictyosphaeria cavernosa (Okuda et al 1997a) and Valonia utricularis (Okuda et al 1997b) separate into several layers if kept in diluted buffer solu-tions (unpublished observations).…”