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The influence of pH 3-10 on the growth, motility and photosynthesis in Euglena gracilis was demonstrated during a 7-d cultivation. The cells did not survive at pH < 4 and > 8, highest growth rate being detected at pH 7. Motility followed a similar pattern as growth rate. Photosynthetic response curves were shown to be of the same type over the whole pH range. High respiration was characteristic for cells grown at pH 5 and 6, the lowest one at 7. At high and also at low pH more active respiration was found which can be considered as a protective response on proton stress. Respiration was not completely inhibited with potassium cyanide. Photosynthesis was the most effective at pH 6; lower and higher pH decreased photosynthetic efficiency. pH affected more the growth rate than the photosynthesis.

Effects of short-term (1 h exposure) and long-term (7 d exposure) aluminium stress on photosynthesis and reproductive capacity have been studied in Euglena gracilis strain Z. Following concentrations of Al tot (added as AlCl 3 ) were tested: 0.5 mg L -1 , 1.0 mg L -1 , 1.5 mg L -1 , 2.5 mg L -1 , 5.0 mg L -1 , 7.5 mg L -1 , 10.0 mg L -1 , and 15.0 mg L -1 Al, respectively. Growth rates at different aluminium concentrations did not show significant differences, except at 15.0 mg L -1 Al. Initial respiration was higher in long-term than in the short-term experiments. It is supposed that an energy-dependent mechanism of excretion of aluminium ions has been active in the stressed cells. Consequently, the cells of E. gracilis after longterm exposure to aluminium are believed to be more acclimatised to the aluminium stress. Photosynthetic efficiency (PE) has been negatively affected by aluminium in all experiments performed. Differences between control algae and those treated with aluminium were significant in all cases. PE in long-term experiments was in general significantly higher at all concentrations of aluminium studied, compared to the short-term experiments. The aluminium concentrations tested led only to a general decrease in PE while the level of decrease was not especially concentration-dependent. In general, aluminium tolerance of E. gracilis can be estimated as low, especially by short-term exposure. However, good acclimatisation capacity of this green flagellate to aluminium doses by long-term exposure can be supposed. Wirkungen von Kurz-und Langzeit-Aluminium-Stress auf Photosynthese, Respiration und Reproduktions-Kapazität eines einzelligen grünen Flagellaten, Euglena gracilisKulturen von Euglena gracilis werden über 1 h und über 7 d gegen 0.5 mg L -1 , 1.0 mg L -1 , 1.5 mg L -1 , 2.5 mg L -1 , 5 mg L -1 , 7.5 mg L -1 , 10 mg L -1 und 15 mg L -1 Aluminium aus AlCl 3 8exponiert. Die Wachstumsrate zeigt mit Ausnahme der höchsten Al-Konzentration keine Beeinflussung. Die initiale Respiration ist in der Langzeitexposition höher als im Kurzzeitexperiment. Als Ursache wird angenommen, dass unter Stresseinfluss ein energieabhängi-ger Mechanismus der Exkretion von Aluminiumionen in den Zellen induziert wird. Als Konsequenz sind die langzeitig exponierten Zellen von E. gracilis stärker an den Stress akklimatisiert. Die photosynthetische Effizienz wird durch Aluminiumionen unter allen Versuchsbedingungen gegenüber der Kontrolle signifikant negativ beeinflusst, wobei keine Konzentrationsabhängigkeit nachzuweisen ist. Im Langzeitexperiment war unter allen Versuchsbedingungen die photosynthetische Effizienz höher als im Kurzzeitversuch. Allgemein ist die Aluminium-Toleranz von E. gracilis als gering anzusehen, speziell im Kurzzeitexperiment, wäh-rend im Langzeitexperiment eine gute Akklimatisationskapazität angenommen werden kann.

The responses of the growth rate, motility, and cell shape in the green flagellate Euglena gracilis to different concentrations of waste water substances from the pulp and paper industry were tested in a long-term study (7 days). Samples before (uncleaned sample) and after (cleaned sample) the treatment in a cleaning system were studied. The influence of different doses of UV-B radiation on cell shape and motility was also investigated. No statistically significant effects of increasing concentrations of the waste substances both before and after the cleaning process (except inhibition by the undiluted uncleaned effluent) on the growth rate in E. gracilis were observed. Cell shape turned out to be an unreliable physiological parameter for assessing the toxicity at lower concentrations of waste water substances. No significant patterns could be observed in the response of the cell shape to the different concentrations of the waste water substances or to UV-B radiation. Motility has been concluded to be a more sensitive parameter than cell shape. However, no clear patterns were observed in the response of the motility to the different concentrations of the waste water substances studied. Increasing concentrations of the uncleaned sample demonstrated a defense against UV-B radiation, due to the high absorbance in the UV-B range, when effects on motility were examined. We conclude that contrary to the results reported in the literature earlier, cell shape and motility of E. gracilis are not universal physiological parameters for bioassessment at lower concentrations of toxic substances, including metals such as copper and zinc from the pulp and paper industry. The long-duration tests had, in general, higher significance than those of short duration.