engleski

Diatom Thalassiosira weissflogii in oligotrophic versus eutrophic culture: models and ultrastructure

Populations of marine diatom Thalassiosira weissjlogii were grown in continuous cultures enriched with f/2 medium. One of the two contrasting cultures ('eutrophic') received 5.6 times more nutrients than the other ('oligotrophic'). Two mathematical models are analyzed to estimate eutrophication differences. The second model based chaelis-Menten uptake and Droop growth shows that cells in the eutrophic culture should bave about 56% higher content of silica which is the limiting nutrient. Diatom samples were prepared for the transmission electron microscopy after cells have been kept in chemostats for 37 days. The structure of diatom cells was investigated and a comparison is made between grown in oligotrophic and eutrophic conditions. In eutrophic culture, dividing cells were encountered more frequently while cell concentration was approximately equal in both chemostats. The central vacuole of cells in eutrophic culture accumulated dispersed and compact materiai from amorphous to spherical share. In same cells the large central vacuole had fibrilar and peppered dense materials in addition to translucent granules, vesicules and multivesicular bodies. In the cytoplasm we found increased number of multivesicular bodies, dense and lucent granules same of which enclose membrane particles and lucent vesicules. Dense material depositions observed in the vacuole are also seen in the cytoplasm associated with organelles, mitochondria and plasmalemma. Cells have well-developed, active and slightly increased number of dictyosome (5-6). Some dictyosomes with dense secretory material in the cistern are apparently engaged in a granule formation process. Functional significance of dense materiai in the central vacuole, which has not been observed in cells grown in oligotrophic condition, is discussed.

Eutrophication measure; Diatom; Modelling; Cell organelles; Vacuoles; Storage material; Electron microscopy

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