In the cultures of the alga Chlamydomonas reinhardtii, division rhythms of any length from 12 to 75 h were found at a range of different growth rates that were set by the intensity of light as the sole source of energy. The responses to light intensity differed in terms of altered duration of the phase from the beginning of the cell cycle to the commitment to divide, and of the phase after commitment to cell division. The duration of the pre-commitment phase was determined by the time required to attain critical cell size and sufficient energy reserves (starch), and thus was inversely proportional to growth rate. If growth was stopped by interposing a period of darkness, the pre-commitment phase was prolonged corresponding to the duration of the dark interval. The duration of the post-commitment phase, during which the processes leading to cell division occurred, was constant and independent of growth rate (light intensity) in the cells of the same division number, or prolonged with increasing division number. It appeared that different regulatory mechanisms operated through these two phases, both of which were inconsistent with gating of cell division at any constant time interval. No evidence was found to support any hypothetical timer, suggested to be triggered at the time of daughter cell release.
- MeSH
- buněčný cyklus účinky záření MeSH
- časové faktory MeSH
- Chlamydomonas reinhardtii cytologie růst a vývoj účinky záření MeSH
- cirkadiánní proteiny Period metabolismus MeSH
- cirkadiánní rytmus genetika účinky záření MeSH
- kultivované buňky MeSH
- mutace genetika MeSH
- světlo MeSH
- tma MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
BACKGROUND: Selenium is a trace element performing important biological functions in many organisms including humans. It usually affects organisms in a strictly dosage-dependent manner being essential at low and toxic at higher concentrations. The impact of selenium on mammalian and land plant cells has been quite extensively studied. Information about algal cells is rare despite of the fact that they could produce selenium enriched biomass for biotechnology purposes. RESULTS: We studied the impact of selenium compounds on the green chlorococcal alga Scenedesmus quadricauda. Both the dose and chemical forms of Se were critical factors in the cellular response. Se toxicity increased in cultures grown under sulfur deficient conditions. We selected three strains of Scenedesmus quadricauda specifically resistant to high concentrations of inorganic selenium added as selenite (Na2SeO3) - strain SeIV, selenate (Na2SeO4) - strain SeVI or both - strain SeIV+VI. The total amount of Se and selenomethionine in biomass increased with increasing concentration of Se in the culturing media. The selenomethionine made up 30-40% of the total Se in biomass. In both the wild type and Se-resistant strains, the activity of thioredoxin reductase, increased rapidly in the presence of the form of selenium for which the given algal strain was not resistant. CONCLUSION: The selenium effect on the green alga Scenedesmus quadricauda was not only dose dependent, but the chemical form of the element was also crucial. With sulfur deficiency, the selenium toxicity increases, indicating interference of Se with sulfur metabolism. The amount of selenium and SeMet in algal biomass was dependent on both the type of compound and its dose. The activity of thioredoxin reductase was affected by selenium treatment in dose-dependent and toxic-dependent manner. The findings implied that the increase in TR activity in algal cells was a stress response to selenium cytotoxicity. Our study provides a new insight into the impact of selenium on green algae, especially with regard to its toxicity and bioaccumulation.
- MeSH
- biomasa MeSH
- Scenedesmus metabolismus růst a vývoj účinky léků MeSH
- seleničitan sodný metabolismus toxicita MeSH
- selenomethionin metabolismus MeSH
- síra metabolismus MeSH
- sloučeniny selenu toxicita MeSH
- thioredoxin-disulfidreduktasa metabolismus MeSH
- vztah mezi dávkou a účinkem léčiva MeSH
- Publikační typ
- práce podpořená grantem MeSH
Cyclin-dependent kinases (CDK) play a key role in coordinating cell division in all eukaryotes. We investigated the capability of cyclin-dependent kinases CDKA and CDKB from the green alga Chlamydomonas reinhardtii to complement a Saccharomyces cerevisiae cdc28 temperature-sensitive mutant. The full-length coding regions of algal CDKA and CDKB cDNA were amplified by RT-PCR and cloned into the yeast expression vector pYES-DEST52, yielding pYD52-CDKA and pYD52-CDKB. The S. cerevisiae cdc28-1N strain transformed with these constructs exhibited growth at 36 degrees C in inducing (galactose) medium, but not in repressing (glucose) medium. Microscopic observation showed that the complemented cells had the irregular cylindrical shape typical for G2 phase-arrested cells when grown on glucose at 36 degrees C, but appeared as normal budded cells when grown on galactose at 36 degrees C. Sequence analysis and complementation tests proved that both CDKA and CDKB are functional CDC28/cdc2 homologs in C. reinhardtii. The complementation of the mitotic phenotype of the S. cerevisiae cdc28-1N mutant suggests a mitotic role for both of the kinases.
- MeSH
- Chlamydomonas reinhardtii enzymologie MeSH
- cyklin-dependentní kinasy chemie metabolismus MeSH
- financování organizované MeSH
- molekulární sekvence - údaje MeSH
- mutace genetika MeSH
- proteinkinasa CDC28, S cerevisiae metabolismus MeSH
- Saccharomyces cerevisiae cytologie enzymologie MeSH
- sekvence aminokyselin MeSH
- sekvenční seřazení MeSH
- teplota MeSH
- testy genetické komplementace MeSH
- transformace genetická MeSH
- zvířata MeSH
- Check Tag
- zvířata MeSH
