Original paper

Conspicuous forms of keritomic thylakoids in Trichormus variabilis

Šmarda, Jan; Hindák, František


Cells of Trichormus variabilis frequently show keritomy of their thylakoids; this is most extensive in heterocytes, least extensive in akinetes. The flat vesicles separate both their biomembrane leaflets from each other, while being keritomized, extend their volume and acquire irregular rounded and curly forms. They oppress each other, outer surfaces of neighbouring thylakoids lying closely at each other. In this way, the vesicles gain quite irregular, bizarre forms, with only traces or no cytoplasm between them, formed by a single or two membranes. Areas of keritomized thylakoids originate at the cell poles and, at last, the full cell interior may get transformed into them; in this way, the cell degenerates. In heterocytes of all four strains Trichormus variabilis, which we had at our disposal, the highly keritomized thylakoid membranes reach the form of parallel narrow tubules, arranged in a highly regular pattern of p2 symmetry. The basic cytoplasm is closed within them or spreads around. This particular organelle originates in the heterocyte polar region (or both) and extends to the centroplasm. It is clearly remote from the “prolamellar-like body” of Jensen (1985), but is homologous with the “localized membrane elaboration” reported by Cmiech, Leedale & Reynolds (1986).