Untersuchungen über die chemische Zusammensetzung des Zellsaftes der DiatomeeCoscinodiscus wailesii (Bacillariophyceae, Centrales)

Abstract

A sample of cells of the plankton diatomCoscinodiscus wailesii was cultivated at 15° C under 14 hours illumination per day by fluorescent lamps (ca. 1000 lux). The aerated culture medium consisted of Erdschreiber solution of about 30 ‰ salinity enriched (afterLewin 1965) with B (5 · 10⁻⁵ m) and provided with infusorial earth (1 g/l) as a source of Si and trace elements. When the cell concentration reached about 100 per ml the diatoms were sifted off by a piece of plankton cloth (mesh width 200µ) and rinsed on the sieve by artificial Li-sea-water. After this treatment most of the Li-solution still adhering was removed by filter paper; the remaining rest imbibed in the free accessible room of the cytoplasm as well as in the cell walls and in interstitial rooms between cells was determined by flame photometry as apparent free space (AFS). All results were obtained from a single sample only; they have therefore to be regarded as preliminary. Comparing these results with the information revealed by former investigations on the cell sap of other marine algae (Kesseler 1964, 1966) no uncommon facts could be established: Potassium and chloride proved to be the main intracellular ions, while sodium was restricted to about 0.25 times its medium concentration; NH ^·₄ was not detectable. Mg^··, Ca^··, and H₂PO′₄ were present in relatively small amounts, while the sulfate concentration was rather high, and thus obviously compensating for the deficit in chloride ions. Similar relations, but more pronounced, were found inDesmarestia viridis. Acidity of cell sap, determined by means of Merck indicator paper, was p_H 5. Considering the dilution of the sample by the artificial Li-sea water, and the buffering effect of H₂PO₄ ions (probably from the cytoplasm), the p_H of the original sap might have been about 4. The specific gravity of artificial sap (prepared in agreement with the analytical results and determined arcometrically) was 1,0287 g/cm³ at 20° C, while the density of the culture medium, at the same temperature, was 1,0243 g/cm³. The chemical properties of the cell sap ofCoscinodiscus wailesii provide in no way suitable means of buoyancy, as could be demonstrated for the cell sap ofNoctiluca (Kesseler 1966). This finding contradicts results by the Russian investigatorsBeklemishev,Petrikova &Semina (1961) employing ultramicrochemical methods on samples of cell sap from single cells of the rather closely related giant speciesEthmodiscus rex.

Zusammenfassung

1. Die vorläufigen Ergebnisse von chemischen Analysen des Zellsaftes vonCoscinodiscus wailesii werden mitgeteilt und den vonBeklemishev et al. (1961) an Zellsaftproben vonEthmodiscus rex gewonnenen Resultaten gegenübergestellt.

2. Eine eingehende kritische Diskussion der beiderseitigen, völlig widersprüchlichen Ergebnisse liefert keine Anhaltspunkte zur befriedigenden Erklärung dieser Diskrepanzen, die weiteren Untersuchungen vorbehalten bleiben muß.