ABSTRACT
This study aims to contribute to the suty of sub-cellular characters that may be used in the taxonomy of filamentous Phaeophyceae. Studies of light and electron microscopy transmission provided data on the structure and ultrastructure of the cells in the vegetative stage and plurilocular reproductive structures of H. mitchelliae. Vegetative and reproductive cells of H. mitchelliae are uni-nucleated, coated with a cellulose wall, other polysaccharides and proteins. The presence of a single nucleus, organization of thylakoids in the chloroplasts forming three thylakoids per band, longitudinally arranged at the major axis of the organelles, and absence of thylakoids in the pyrenoid are similar to those of other Phaeophyceae. H mitchelliae also exhibits ultrastructural characteristics that are generally associated with other species from less advanced orders of Phaeophyceae: the presence of a prominent pyrenoid, perinuclear dictyosomes and plasmodesmatas. The morphology and the organization of chloroplasts as well the presence or absence of pyrenoid are important features in the Phaeophyceae. The formation of a new pyrenoid during differentiation periods was observed in chloroplasts of vegetative cells. Both cells presented a nucleus with a large nucleolus, suggesting an intense metabolic activity. Many osmiophilic bodies called physodes were observed in the cytoplasm of the vegetative and reproductive cells. Cells of matured plurilocular structure of H. mitchelliae differed from vegetative cells due to its reduced size, dense cytoplasm, and absence of vacuoles.
Key words:
Hincksia mitchelliae; structural organization and ultrastructure