|InterJournal Complex Systems, 1649
|Manuscript Number: |
Submission Date: 2006
|Intrapopulation changes of algae under toxic exposure|
Laboratory populations of microalgae are widely used as sensitive test object for the evaluation of the phytotoxicity of chemicals and waste water streams. The cultures of freshwater green alga Scenedesmus quadricauda (Turp.) Breb. and marine diatom alga Thalassiosira weissflogii (Grunow) Fryxell et Hastle were studied under the influence of different toxicants (heavy metals chromium and silver as a part of water-dissolved salt, pesticide imazalil sulfate). The chromium and silver at concentrations of 0.0001, 0.001 and 0.01 mg/l (low concentrations) were found have an slight influence upon cell number, cell division rates, photosynthetic efficiency and share of alive cells. Any possible changes could be explained on the base of well-known idea of cell population as a complex system with resistant and sensitive cells. Such insignificant differences between control and sample cultures at low concentrations were reversible during the period of experiment. The reason of possible population growth delay under low-level toxic exposure was the arrest of proliferation of some cells rather than deceleration of cell cycle in all cells. At medium concentrations (0.05 mg/l silver and 0.1 mg/l chromium), the effect varied from indifferent to toxic according to algal species and season. At concentrations of the toxicants over 0.05 mg/l for silver and over 1.0 mg/l chromium, a total cell number and proportion of living cells decreased. At the concentration 3.0 mg/l chromium, we observed both undividing and proliferating cells. At high toxicant concentrations (0.1 and 0.5 mg/l silver and 10.0 mg/l chromium), stimulation of cell division preceded the fast death of algal population. On the whole, the freshwater algae were found to be more sensitive to heavy metal action than marine algae. It was shown the existence of algostatic effect of silver after the growth of algal cultures in the presence of high toxicant concentrations. In this case the cell number stayed particularly unchangeable during the period of the experiment. The freshwater algal population behaviour was studied under the pesticide action too. The fungicide imazalil sulfate at concentrations of 0.001 and 1.0 mg/l was found to inhibit the division of cells and imparted to them anomalous increase in size and the formation of gigantic cells, but such state of algae was reversible: giant cells rapidly resumed their division after being transferred to a toxicant-free medium. At concentration of 0.1 mg/l, the division of cells resumed within 1-2 days of intoxication. At high imazalil concentrations (5, 10 and 20 mg/l), division stimulation preceded the fast death of algal population as well as at high chromium and silver concentrations. The selection of the resistant cells within the heterogeneous algal population under high concentration 10.0 mg/l chromium exposure was demonstrated. Changes of the population structural and functional characteristics can be special way of survival in unfavourable conditions. Data on the cell number, their photosynthetic characteristics, population structure and share of alive and dead cells will be appropriate for use to predict the most sensitive ecosystem responses and indicate the permissible amount of toxicants in the environment.
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