Studying the ultrastructure of the marine diatom Seminavis robusta

Abstract

Diatoms are a species-rich group of chromophytes which can be found both in marine and fresh-water environments. Diatoms contribute close to 20% of global primary production and close to 40% of marine primary production, and form the base of the trophic pyramid in many areas of the ocean. The most characteristic feature of diatoms is their ornate silica cell wall, called the frustule.

Seminavis robusta is a species of benthic, pennate diatom. S. robusta is especially well-suited for ultrastructural study because of its large size, up to 100μm, and ,being a benthic diatom adhering to surfaces, allowing the easy, non-intrusive observation of cellular behaviour and life cycle of living cells. They have two large vacuoles and phaeoplasts. The pyrenoids of S. robusta are elongated and run down the inside of the phaeoplasts. The large vacuoles store, among other things, neutral lipids. The nucleus is always located in the centre of the cell and is surrounded by Golgi apparatuses. ER can be found as lengths of double membrane in the cytosol.

In this thesis an attempt was made to design a method of preparation of S. robusta for TEM. During this method development the main focus was on fixatives for both primary and post fixation. There is still much research to be done in this field and future studies should focus on infiltration time during fixation, post fixation and embedding.

In addition to the work done with TEM two different fluorescent probes were tested on S. robusta in CLSM.