Gunter Otto Kirst

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Salinity, together with light, temperature, and nutrients, is one of the abiotic factors affecting algal growth and distribution. Changes in salinity result in immediate water fluxes according to the osmotic gradients. This rapid response is followed by osmotic acclimation through adjustment of the cellular solute concentrations. As a result of these(More)
d-Mannitol-1-phosphate dehydrogenase (EC and d-mannitol dehydrogenase (EC were estimated in a cell-free extract of the unicellular alga Platymonas subcordiformis Hazen (Prasinophyceae), d-Mannitol dehydrogenase had two activity maxima at pH 7.0 and 9.5, and a substrate specifity for d-fructose and NADH or for d-mannitol and NAD+. The K m(More)
The effect of photon fluence rate on the ß-dimethylsulphoniopropionate (DMSP) content of salt-stressed eulittoral green macroalgae from different geographic regions was determined. At 55 μmol photons m−2s−1 DMSP increased continuously with increasing salinities up to 68‰ in Ulothrix implexa, Ulothrix subflaccida, Enteromorpha bulbosa and Acrosiphonia arcta(More)
Following small hypo-osmotic shocks, ion concentrations (Na+, K+, Cl-) in Platymonas subcordiformis decreased; this was due mainly to an increase of cell volume. With larger hypo-osmotic stresses, the decrease of ion concentration continued and, additionally, extrusion of mannitol was observed. The ion and mannitol concentrations were not regained after 240(More)
Ionic responses to alteration in external and internal pH were examined in an organism from a marine-like environment. Vacuolar pH (pHv) is about 4.9–5.1, constant at external pH (pHo) 5–8, while cytoplasmic pH (pHc) increases from 7.3 to 7.7. pHc regulation fails above pHo 9, and this is accompanied by failure of turgor regulation. Na+ increases above pHo(More)
The Antarctic ice diatom Amphiprora kufferathii Manguin is always accompanied by epiphytic bacteria in its natural habitat. To investigate the nature of this relationship, axenic cultures of A. kufferathii were obtained by ampicillin treatment. Diatom cultures without bacteria were less dense. The bacteria were shown to consume hydrogen peroxide produced by(More)
The tertiary sulphonium compound, β-dimethylsulphoniopropionate (DMSP) and the quaternary ammonium compounds glycine betaine and homarine are important osmotica in Platymonas subcordiformis cells. Following hypersaline stresses the compounds were accumulated after a lag period of 3 h and equilibrium concentrations were reached 6 h later. In contrast to(More)
Photosynthesis-irradiance relationships and the carbon metabolism of different ice algal assemblages collected from Weddell Sea pack ice were investigated during the EPOS 1 cruise. Infiltration- and interstitial assemblages exhibited the photosynthetic characteristics of high-light adapted ice algae with a mean assimilation number of 1.81±0.93 mg C (mg Chl(More)
The photosynthetic incorporation of H14CO3 - by the alga Platymonas subcordiformis decreased with increasing concentrations of NaCl in the medium. There was no correlation between the response of P. subcordiformis to salinity in high or low NaCl-concentrations in the growing solution. When other osmotic substances were used (KCl, sucrose, sorbitol, manitol,(More)
Ion compositions (K+, Na+ Mg2+, Ca2+, Cl-, phosphate) of the euryhaline algae, Platymonas subcordiformis, Chlorella salina, grown in media with a salinity range from 0.1 to 0.6 M NaCl and of the fresh-water algae, Ankistrodesmus braunii and Scenedesmus obliquus, were compared. Enhancement of ion concentrations with increasing salinity in Platymonas was(More)