Nephrocytium limneticum (G. M. Smith) G. M. Smith 1933: 503

Liu, Xudong, Zhu, Huan, Liu, Benwen, Liu, Guoxiang & Hu, Zhengyu, 2017, Phylogeny and morphology of genus Nephrocytium (Sphaeropleales, Chlorophyceae, Chlorophyta) from China, Phytotaxa 319 (1), pp. 84-92 : 86

Nephrocytium limneticum (G. M. Smith) G. M. Smith 1933: 503

Synonyms: — Gloeocystopsis limnetica G. M. Smith 1916 , Nephrocytium agardhianum var. szolnokiense Kiss & Szabó 1975 . Holotype: —G. M. Smith 1933: 503. Depicted in Komárek & Fott (1983, pl. 157:3).

Description

Colonies (rarely unicellular) were microscopic with 2–32 (often 4–8; Figs 1–3 ) cells embedded in mucilaginous envelope ( Fig. 5 ) and forming spherical to pyramidal to amorphous masses approximately 30–80 μm diameter. Mucilaginous material usually enveloped each group of cells, often in clusters following sporulation ( Fig. 3 ). Cells were kidney-shaped or oval to somewhat curved and were asymmetric with rounded-acuminate to broadly rounded and not tapered apices that were 11–19 μm long and 5–14 μm wide (Figs 1,2,13). Chloroplasts were single-lobed parietal with a single, small pyrenoid when young that gradually fragmented and diffused (Figs 4,13) with a large pyrenoid (or in rare instances, two large pyrenoids) when mature (Figs 5,14). Asexual reproduction was by autospores (Figs 3,6), 2–4–8 per sporangium and released by dissolution, or sometimes rupturing, of the sporangial wall. Mother cell wall fragments were usually dissolved in the colonial mucilage, but occasionally a distinctive remnant was observed. Sexual reproduction and flagellated stages are unknown.

The TEM observation revealed that the cell wall was multilayered, and the surfaces of the daughter cell walls were not smooth ( Figs 13–15 ). Dense and fine ribs were thought to form an irregular network and cover the surface, approximately 0.1–0.2 μm long. The ultrastructure changed with age and was relatively smooth when old or expanded ( Fig. 14 ). The mutually perpendicular cellulose fibrils between adjoining layers, as observed in Oocystis , were not visible. The global pyrenoid with a homogenous matrix was situated and surrounded by several thick starch sheathes ( Fig. 14 ). Thylakoids extended the length of the chloroplast and occurred in stacks of four to twelve (Figs 13,14) but never traversed the pyrenoid matrix ( Fig. 14 ). Numerous single lenticular starch grains were visible inside chloroplasts ( Fig. 13 ).

Figures

FIGURES 1–12. Light microscopy of Nephrocytium limneticum cultured (1–6), and Nephrocytium agardhianum in the field (7), and cultured (8–12). 1. Young cells in colony. 2. Old cells in colony. 3. Autospores in sporangium. 4. Autofluorescence showing the shape of chloroplasts. 5. Negative stain by ink showing the mucilage envelope. 6. Sporangia in colony. 7 Colony in the field habit. 8. Young cells in colony. 9. Old cells in colony. 10.Autofluorescence showing the shape of chloroplasts. 11. Negative stain by ink showing the mucilage envelope. 12. Autospores in a sporangium. Scale bar 10 μm.

FIGURES 13–18. Transmission electron microscopy of Nephrocytium limneticum (13–15) and Nephrocytium agardhianum (16–18). 13,15. Longitudinal section of a cell, showing the undulated surface of cell wall. 14,17. Cells within the mother cell wall, showing the presence of the pyrenoid and the smooth mother cell wall. 15,18. Details of cell wall. (CW=cell wall, MCW=mother cell wall, P=pyrenoid, St=starch sheath, S=starch grains, t=thylakoids). Scale bar 2 μm (13–14, 16–17), 0.5 μm (15), 0.2 μm (18).