Cytological and taxonomic studies of the Euglenales. I. Ultrastructure and envelope elemental composition in Trachelomonas

Abstract

The ultrastructural cytology, envelope microarchitecture and elemental composition are described for species from three of Pringsheim's subgeneric categories of the euglenoid flagellate, Trachelomonas. Except for differences in chloroplast number and pyrenoid morphology, cellular organization in T. bulla, T. zorensis and T. lefevrei is similar; however, based on our finding that T. lefevrei has inner and outer paramylon caps over the pyrenoid, we propose that this species be moved from its present position in the subgroup with inner pyrenoids, to the subgroup with double-sheathed pyrenoids. Envelope microarchitecture, elemental composition and colour are correlated in each of the species. Elemental analyses indicate that envelopes or regions of envelopes with high iron content have a granular substructure, whereas those rich in manganese have a needle-like microcrystalline substructure. Envelopes of T. bulla never appear dark in the light microscope (L.M.) and have a granular microarchitecture with iron as the major element. In T. zorensis and T. lefevrei, envelopes manifest a range of colour from hyaline to dark in the L.M., with shifting ratios of Fe: Mn as envelopes darken. When both elements are present in the same envelope, they are spatially segregated, with Fe-rich granular regions and Mn-rich needle-like microcrystalline regions; some hyaline envelopes are largely granular, while some dark envelopes are exclusively microcrystalline. The utility of ultrastructural and envelope characteristics as taxonomic criteria is discussed.