Experimental studies on the benthic phases of haptophyceae II. studies on ‘Aged’ benthic phases of Pleurochrysis scherffelii E. G. Pringsh

Abstract

A study has been made of the ‘recovery’ processes of benthic cells of Pleurochrysis scherffelii ‘aged’ in two year-old cultures. Water-line non-motile cells and those from the bottom of the flasks were utilized. The water-line material showed a reduction in cell size and contents, whereas cells from the flask bottom showed an increase in cell diameter with reduction in chromatophore size and increase in the volume of the leucosin reserve, and in the number of lipid vesicles. Both types of nonmotile phase failed to produce motile cells when transferred to higher temperatures and brighter illumination whilst still in the ‘aged’ medium. Transference of the aged benthic cells from the bottom of the flask to ‘enriched’ sea water, to fresh sea water without enrichment, to the aged medium enriched with nitrate-N, phosphate-P and trace elements, or to fresh sea water enriched with soil extract, resulted in the onset of cell division and release of motile cells within 12–24 h, with the general indication that micronutrients, organic or inorganic, were responsible for the ‘pace’ of cell division. Under similar conditions, the aged water-line cells showed cell division when transferred to fresh enriched media, but no release of motile cells, and invariably death of the mass of daughter cells followed the initial rapid proliferation. In aged media of different biological history, the ‘young’ benthic cells grown on sea water agar showed further cell division, but with the development of different morphological forms from those obtained in the aged ‘ Pleurochrysis’ medium, and without release of motile cells. Short-term immersions of the aged benthic cells from the flask bottom in enriched media (for 1, 3, 6 and 9 h) all resulted in cell division and release of motile cells when the material was resuspended in the original ‘aged’ medium, the length of immersion in the enriched medium having a direct influence on the time for which cells would continue dividing. Darkening of chromatophore colour, with apparent increase in carotenoid content, was a characteristic feature of the ‘recovery’ process. Extraction of pigments and measurement of absorption maxima showed that the same pigment content could be detected qualitatively both in the bleached ‘aged’ benthic cells and the ‘young’ benthic cells in fresh media. An unusual feature was observed in the changed staining properties of the leucosin reserve of the ‘aged’ benthic cells when treated with Cresyl Blue. Relatively small numbers of cells ( ca 10–12% of a population) showed the characteristic rose-red colouration. In enriched media this proportion increased to ca 80 % over 3–4 days with increased light and temperature. Under similar conditions, aged cells in the ‘aged’ medium showed an increase in the cells giving a vesicle colouration over the first few days, but thereafter the numbers of cells so reacting steadily decreased. The results of these and other experiments suggested that the colour reaction is associated with certain levels of metabolic activity in the cells and there was no evidence that failure of the stain to penetrate the cell membrane was a cause of the lack of vesicle colour in a large proportion of the aged cells. The relevance of this experimental work to field observations on the benthic phases of Haptophyceae is also discussed.