Ontogenetic analysis of siliceous cell wall formation in Triparma laevis f. inornata (Parmales, Stramenopiles)

Abstract

Triparma laevis f. inornata is a unicellular alga belonging to the Bolidophyceae, which is most closely related to diatoms. Like diatoms, T. laevis f. inornata has a siliceous cell wall. The cell wall of T. laevis f. inornata consists of four round plates (three shields and one ventral plate) and one dorsal and three girdle plates. But, unlike diatoms, T. laevis f. inornata cells can grow when concentrations of silica are depleted. We took advantage of this ability, using TEM to study the ontogeny of the siliceous plate, pattern center formation, and development. Two types of pattern centers (annulus and sternum) were observed in the early and middle stage of plate formation. During their formation, the annuli were initially crescent‐shaped but eventually their ends fused to make a ring. Only outward silica deposition of the branching ribs occurred on the growing annulus until it became a ring, resulting in an unfilled circle inside the annulus. The pattern center of the shield plate was always an annulus, but in ventral plates both annulus and sternum were observed. The annuli and sterna in T. laevis f. inornata round plates were very similar to the annuli and sterna in diatom valves. These results suggested that the round plates of Parmales are homologous to diatom valves. This information on the plate ontogeny of T. laevis f. inornata provides new insights into the evolution of the siliceous cell wall in the Parmales and diatoms.

Swimming, gliding, and rolling toward the mainstream: cell biology of marine protists

“…The closest relatives of diatoms, the parmales, do not require their silica shells and the biosynthesis of the silica plates in Triparma laevis can be controlled by simply manipulating silicate availability. Yamada et al. (2019) demonstrated that the early steps of silica wall formation in T. laevis are homologous to the process of frustule formation in diatoms, confirming that parmales provide an alternative system in which to study frustule formation.…”

Biogenic silica accumulation in picoeukaryotes: Novel players in the marine silica cycle

“…For example, Triparma laevis (Bolidophyceae), which has some picoeukaryotic‐sized cells that measure <3 μm in diameter, uses dSi to construct silica shields around individual cells (Booth & Marchant, 1987 ; Kuwata et al, 2018 ; Yamada et al, 2014 ). T. laevis has some cellular structures for formation of silica shields that are analogous to diatoms but, unlike most diatoms, seems to lack an obligate need for dSi for growth (Yamada et al, 2016 ; Yamada et al, 2018 ). However, any potential purpose of bSi accumulation in most picophytoplankton is currently unknown.…”

New clade of silicified bolidophytes that belong to Triparma (Bolidophyceae, Stramenopiles)

“…The common ancestor of bolidophytes and its sister lineage, diatoms, may already have had the silicified form in their life cycle, since the siliceous cell wall of both groups has been considered a synapomorphy based on morphological and ontogenetic similarity (Mann & Marchant 1989;Yamada et al 2019). In addition, a previous study argued that the silicified species have a potentially dimorphic life cycle, because flagellated cells have been observed in cultures of silicified T. laevis (Ichinomiya et al 2016).…”