| 1. |
- Bott, Lukas Thomas, et al.
(author)
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Coulomb dissociation of O-16 into He-4 and C-12
- 2023
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In: NUCLEAR PHYSICS IN ASTROPHYSICS - X, NPA-X 2022. - : EDP Sciences. - 2100-014X. ; 279
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Conference paper (peer-reviewed)abstract
- We measured the Coulomb dissociation of O-16 into He-4 and C-12 within the FAIR Phase-0 program at GSI Helmholtzzentrum fur Schwerionenforschung Darmstadt, Germany. From this we will extract the photon dissociation cross section O-16(alpha,gamma)C-12, which is the time reversed reaction to C-12(alpha,gamma)O-16. With this indirect method, we aim to improve on the accuracy of the experimental data at lower energies than measured so far. The expected low cross section for the Coulomb dissociation reaction and close magnetic rigidity of beam and fragments demand a high precision measurement. Hence, new detector systems were built and radical changes to the (RB)-B-3 setup were necessary to cope with the high-intensity O-16 beam. All tracking detectors were designed to let the unreacted O-16 ions pass, while detecting the C-12 and He-4.
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| 2. |
- Danilov, Roman A, et al.
(author)
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Applicability of growth rate, cell shape and motility of Euglena gracilis as physiological parameters for bioassessment at lower concentrations of toxic substances: an experimental approach.
- 2001
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In: Environmental Toxicology. - 1520-4081 .- 1522-7278. ; 16:1, s. 78-83
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Journal article (peer-reviewed)abstract
- 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.
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| 3. |
- Danilov, Roman A, et al.
(author)
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Periphyton communities on natural substrata in eu-, meso- and oligotrophic lakes at higher latitude
- 2002
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In: Biologia. - 0006-3088 .- 1336-9563. ; 57:4, s. 433-436
-
Journal article (peer-reviewed)abstract
- Natural epiphyton and epilithon communities were studied in eu-, meso- and oligotrophic lakes at latitude of 62degrees54' N in Vasternorrlands region of Sweden. The samples of epiphyton as well as epilithon (three per lake) were identical and specific for each lake studied. Both epiphytic and epilithic communities consisted of members of three classes of algae - Cyanophyceae, Chlorophyceae and Bacillariophyceae. The highest species diversity was detected within Chlorophyceae while Cyanophyceae and Bacillariophyceae contained the same amount of species. In general, epiphyton and epilithon shared 44% of species identified. However, both epiphyton and epilithon showed distinct patterns between lakes of different trophic level. Epiphyton in the eutrophic lakes were clearly dominated by Cyanophyceae (Bacillariophyceae co-dominated in one of the eutrophic lakes). Both mesotrophic and oligotrophic lakes were signed by high abundance of Chlorophyceae and almost complete absence of Bacillariophyceae and Cyanophyceae. Epilithic communities in the oligotrophic lakes had higher species diversity than those in the meso- and eutrophic lakes studied. Chlorophyceae were dominant in two eutrophic lakes and Cyanophyceae only in one eutrophic lake, Chlorophyceae as well as Bacillariophyceae were abundant in the oligotrophic lakes. Cluster analysis based on species presence-absence led to a sufficient resolution between both epiphytic and epilithic communities of eutrophic environments, on the one hand, and epiphytic and epilithic communities of meso- and oligotrophic environments, on the other.
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| 4. |
- Danilov, Roman A, et al.
(author)
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Phytoplankton communities at different depths in two eutrophic and two oligotrophic temperate lakes at higher latitude during the period of ice cover
- 2001
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In: Acta Protozoologica. - 0065-1583 .- 1689-0027. ; 40:3, s. 197-201
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Journal article (peer-reviewed)abstract
- Phytoplankton communities at different depths and at different locations within each lake were studied during the period of ice cover (from January to March) in two eutrophic and two oligotrophic lakes in North-Eastern Sweden. Cryptophyceae, Dinophyceae and Euglenophyceae were dominant during the whole period of investigation in eutrophic environments. Bacillariophyceae, Chlorophyceae, Chrysophyceae and Cyanophyceae were only occasionally found both in eutrophic and oligotrophic lakes. Both in eutrophic and oligotrophic lakes diversity as well as abundance of phytoplankton were considerably higher immediately under ice than near the bottom. No differences in horizontal distribution of phytoplankton assemblages were detected within each lake. However, vertical differences were more profound. It is speculated that both light availability and increased ion concentration under the ice cover can be viewed as main factors determining phytoplankton communities.
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| 5. |
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| 6. |
- Danilov, Roman, et al.
(author)
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Autumn phytoplankton assemblages in temperate lakes of different eutrophication level in the middle part of Sweden
- 2000
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In: Nordic Journal of Botany. - : Wiley. - 0107-055X .- 1756-1051. ; 20:2, s. 225-232
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Journal article (peer-reviewed)abstract
- Phytoplankton assemblages were studied during autumn 1998 in oligo-, meso- and eutrophic lakes in central Sweden (62°54'N). Differences in phytoplankton assemblages have been detected both in space and time. In eutrophic lakes coccoid Chlorophyceae dominated quantitatively during September and October. Diatoms were the most diverse group in all types of lakes in September and in meso- and oligotrophic lakes in October. In November Cryptophyceae became the most abundant group in all lakes. The total richness of species decreased in the meso- and oligotrophic environments in November compared to September and October, whilst in the eutrophic environment it remained almost unchanged. Cluster analyses, using both presence-absence and presence-absence in combination with abundance matrices, showed similar results and a good resolution between the lakes of different eutrophication conditions. We conclude that the phytoplankton assemblages of the lakes studied depended on the trophic conditions and thus they can be used for resolution between different eutrophication levels.
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| 7. |
- Danilov, Roman, et al.
(author)
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Comparative studies on the usefulness of seven ecological indices for the marine coastal monitoring close to the shore on the swedish east coast
- 2001
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In: Environmental Monitoring & Assessment. - 0167-6369 .- 1573-2959. ; 66:3, s. 265-279
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Journal article (peer-reviewed)abstract
- The simultaneous behaviour of seven ecological indices (Hurlbert's, Margalef's, Menhinick's, Shannon's, species number, Jaccard's and saprobic index) was studied based on phytoplankton data close to the shore on the East coast of Sweden during the summer 1998. The sampling stations had a similar eutrophication level and were located in bays. Standard phytoplankton databases were used in calculating the indices, which were later compared using cluster analysis. Hurlbert's, Margalef's, Menhinick's, Shannon's and species number indices, as measure of community diversity, produced similar trends which often differed from those based on Jaccard's index of similarity. However, the simultaneous use of these indices was found meaningful as a possible part of the monitoring close to the shore. The application of a saprobic index lead to erroneous conclusions in the studied case.
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| 8. |
- Danilov, Roman, et al.
(author)
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Comparison of usefulness of three types of artificial substrata (glass, wood and plastic) when studying settlement patterns of periphyton in lakes of different trophic status
- 2001
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In: Journal of Microbiological Methods. - 0167-7012 .- 1872-8359. ; 45:3, s. 167-170
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Journal article (peer-reviewed)abstract
- Usefulness of three types of artificial substrata (glass, wood and plastic) was tested when studying settlement patterns of periphyton in lakes of different trophic status. Strictly eu-, meso- and oligotrophic lakes in central Sweden were chosen as objects of the study. Glass slides, glass tubes, pieces of plastic (PVC) and pieces of wood of similar dimensions were placed for 9 weeks in July-August vertically 3 cm above bottom at a total depth of ca. 30 cm. Substrata were located at well-illuminated places without any other submerged objects (like macrophytes and stones), which could potentially affect colonisation patterns by algae. Periphyton communities, which colonised both the glass tubes and the pieces of wood tested, were specific enough to enable a clear classification of the lakes studied in eu-, meso- and oligotrophic. Glass tubes turned out to be the most favourable substratum when investigating settlement patterns of periphyton in this study. Although also colonised by periphytic species, wood did not support the same diversity and abundance of species as glass did. No algae were detected on the plastics studied. The plastics were covered entirely by a slime layer of bacteria. It is discussed if the nature of plastics could have some inhibitory effects on algal growth or the slime layer itself may have prevented settlement of algal spores.
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| 9. |
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| 10. |
- Danilov, Roman, et al.
(author)
-
Effects of copper on growth rate, cell shape, motility and photosynthesis in the green flagellate Euglena gracilis in a long-term experiment
- 2000
-
In: Biologia. - 0006-3088 .- 1336-9563. ; 55:4, s. 413-418
-
Journal article (peer-reviewed)abstract
- The green flagellate Euglena gracilis was treated for seven days with concentrations of copper ranging from 0.02 mg L-1 to 2.0 mg L-1. No inhibiting effects were detected in any physiological parameters measured. In general, it seems that enhanced copper concentrations stimulated photosynthetic efficiency (PE) of E. gracilis. Concentrations of copper reported to be critical for the other algae studied (from 0.10 mg L-1 to 0.14 mg L-1) did not show any severe negative effects on E. gracilis. An unusual trend was observed where an increase in PE was followed by an increase in light irradiance necessary to achieve light compensation point. High capacity of E. gracilis to adapt to copper stress is being discussed as a possible explanation for the trends detected.
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| 11. |
- Danilov, Roman, et al.
(author)
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Effects of Cu2+, Ni2+, Pb2+, Zn2+ and pentachlorophenol on photosynthesis and motility in Chlamydomonas reinhardtii in short-term exposure experiments.
- 2001
-
In: BMC Ecology. - : Springer Science and Business Media LLC. - 1472-6785. ; 1:1
-
Journal article (peer-reviewed)abstract
- Background: Heavy metals, especially copper, nickel, lead and zinc, have adverse effects on terrestrial and in aquatic environments. However, their impact can vary depending on the nature of organisms. Taking into account the ability of heavy metals to accumulate in sediments, extended knowledge of their effects on aquatic biota is needed. In this context the use of model organisms (often unicellular), which allows for rapid assessment of pollutants in freshwater, can be of advantage. Pentachlorophenol has been extensively used for decades as a bleaching agent by pulpand paper industry. Pentachlorophenol tends to accumulate in the nature. We aim to determine if photosynthesis and motility can be used as sensitive physiological parameters in toxicological studies of Chlamydomonas reinhardtii, a motile green unicellular alga. It is discussed if photosynthesis and motility can be used as sensitive physiological parameters in toxicological studies. Results: The concentrations studied ranged from 0.1 to 2.0 mg l-1 for copper, nickel, lead and zinc, and from 0.1 to 10.0 mg l-1 for pentachlorophenol. Exposure time was set to 24 h. Copper and pentachlorophenol turned out to be especially toxic for photosynthetic efficiency (PE) in C. reinhardtii. Conclusion: Copper and pentachlorophenol turned out to be especially toxic for PE in C. reinhardtii. Zinc has been concluded to be moderately toxic while nickel and lead had stimulatory effects on the PE. Because of high variance, motility was not considered a reliable physiological parameter when assessing toxicity of the substances using C. reinhardtii. © 2001 Danilov and Ekelund, licensee BioMed Central Ltd.
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| 12. |
- Danilov, Roman, et al.
(author)
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Effects of different levels of UV-B radiation on marine epilithic communities: a short-term microcosm study
- 2000
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In: Scientia Marina. - : Editorial CSIC. - 0214-8358 .- 1886-8134. ; 64:4, s. 363-368
-
Journal article (peer-reviewed)abstract
- Epilithic communities from brackish coastal water of the east coast of Sweden were studied in order to reveal their responses to different levels of UV-B radiation. The experiment was conducted for seven days in an indoor microcosm system. The epilithic communities were exposed daily to different doses of UV-B radiation: 1, 3, 5 and 7 hours, respectively. The intensity of the UV-B radiation used was similar to that in natural environments. After seven days clear shifts both in species composition and community structure were observed. All species of diatoms showed negative correlation with enhanced levels of UV-B. On the other hand, abundance of cyanobacteria was positively correlated with enhanced levels of UV-B (Calothrix aeruginea, R=0.49;Oscillatoria amphibia, R=0.93; Pseudanabaena mucicola, R=0.26). Communities dominated by diatoms and green algae at the initial stage of the experiment did show a drastic decrease in diatom abundance under UV-B stress and finally became dominated by cyanobacteria. Among green algae the abundance of Cladophora sericea correlated positively (R=0.33) with enhanced exposure to UV-B, while Monoraphidium-species exhibited negative correlation to UV-B. Otherwise, no significant correlation between other green algae species identified and UV-B stress could be detected. We conclude that UV-B radiation, even at lower levels, is capable to induce severe changes to marine epilithic communities. The trends revealed in the present study predict a shift from communities dominated by diatoms and green algae to those dominated by cyanobacteria.
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| 13. |
- Danilov, Roman, et al.
(author)
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Effects of increasing doses of UV-B radiation on photosynthesis and motility in Chlamydomonas reinhardtii
- 2000
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In: Folia microbiologica (Prague). - 0015-5632 .- 1874-9356. ; 45:1, s. 41-44
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Journal article (peer-reviewed)abstract
- Effects of increasing doses of UV-B radiation on photosynthetic efficiency (PE) and motility inChlamydomonas reinhardtii were investigated. The exposure time ranged from 10 to 120 min at 0.73 W/m2 UV-B radiation. A decrease in compensation points (CP) was followed by an increase in PE on extending the UV-B treatment up to 60 min. The subsequent increase in PE was accompanied by increasing CPs. Enhanced doses of UV-B radiation thus have a stimulatory effect on the PE inC. reinhardtii. No inhibitory effects could be detected. No statistically significant differences in motility could be observed due to an extremely high variation of values.
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| 14. |
- Danilov, Roman, et al.
(author)
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Effects of pH on the growth rate, motility and photosynthesis in Euglena gracilis
- 2001
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In: Folia microbiologica (Prague). - 0015-5632 .- 1874-9356. ; 46:6, s. 549-554
-
Journal article (peer-reviewed)abstract
- 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.
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| 15. |
- Danilov, Roman, et al.
(author)
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Effects of short-term and long-term aluminium stress on photosynthesis, respiration and reproductive capacity in a unicellular green flagellate (Euglena gracilis).
- 2002
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In: Acta Hydrochimica et Hydrobiologica. - : Wiley. - 0323-4320 .- 1521-401X. ; 30:4, s. 190-196
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Journal article (peer-reviewed)abstract
- 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 Altot (added as AlCl3) were tested: 0.5 mg L-1, 1.0 mg L-1, 1.5 mg L-1, 2.5 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 long-term 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.
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| 16. |
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| 17. |
- Danilov, Roman, et al.
(author)
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Influence of chlorophyll concentrations on the reliability of measurements with an oxygen electrode when studying photosynthetic efficiency in bioassays using microalgae
- 2000
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In: Journal of Applied Phycology. - 0921-8971 .- 1573-5176. ; 12:1, s. 63-67
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Journal article (peer-reviewed)abstract
- Euglena gracilis and Chlamydomonas reinhardtii were used as model organisms to establish the best conditions for studying photosynthetic efficiency using the Light Pipetteexperimental system, which enables sensitive detection of changes in oxygen evolution/consumption and an easy collection and digitalisation of data. Chlorophyll concentrations of 0.005, 0.025, 0.050 and 0.075 mg mL-1 were investigated using different light regimes. Cultures of E. gracilis at the same chlorophyll concentration absorbed more light (measured at 580 μmol m-2 s-1) than those of C. reinhardtii. Cell density had a considerable effect on the reliability of measurements. Chlorophyll concentrations between 0.025 mg(Chl) ml-1 and 0.050 mg(Chl) ml-1 can be recommended when applying the Light Pipette system in bioassays using microalgae.
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| 18. |
- Danilov, Roman, et al.
(author)
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Influence of waste water from the paper industry and UV-B radiation on the photosynthetic efficiency of Euglena gracilis
- 1999
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In: Journal of Applied Phycology. - 0921-8971 .- 1573-5176. ; 11, s. 157-163
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Journal article (peer-reviewed)abstract
- The green flagellate Euglena gracilis has been used as a model organism to elucidate the possible large-scale and short-term effects of waste substances from the pulp and paper industry on photosynthetic efficiency (PE). Different concentrations of waste substances before and after treatment in a cleaning system were studied. The uncleaned sample at concentrations up to 1:10 and the cleaned sample at concentrations up to 1:5 showed stimulating effects on the PE after 7 days of incubation compared to the control. The effects of waste substances on the PE of E. gracilis were also studied in combination with short-term studies (20 and 40 min) of ultraviolet-B radiation (UV-B, 280–320 nm). It was shown that increasing concentrations of the uncleaned sample had continuously stimulating effects on the PE and worked protectively against UV-B radiation. The cleaned sample exhibited no effects, or negative effects, on the PE of E. gracilis together with UV-B radiation compared to the experiments with only UV-B radiation. At the concentration 1:1 of the cleaned sample an increase in the PE was detected due to the high concentration of the coloured substances and a decrease in the UV-B penetration. PE revealed itself to be highly sensitive for detecting toxic effects on E. gracilis and is thus very promising for use in regular toxicity tests of waste water from pulp and paper industry.
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| 19. |
- Danilov, Roman, et al.
(author)
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Responses of photosynthetic efficiency, cell shape and motility in Euglena gracilis (Euglenophyceae) to short-term exposure to heavy metals and pentachlorophenol
- 2001
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In: Water, Air and Soil Pollution. - 0049-6979 .- 1573-2932. ; 132:1-2, s. 61-73
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Journal article (peer-reviewed)abstract
- Euglena gracilis was exposed for 24 hr to concentrations of copper, nickel, lead and zinc ranging from 0.1 to 2.0 mg L-1 and to pentachlorophenol ranging from 0.1 to 10.0 mg L-1. Photosynthetic efficiency (PE) was inhibited by increasing concentrations of the heavy metals. Nickel was found to be the least toxic of the metals to E. gracilis, while the other three metals exhibited similar levels of toxicity. Treatment with pentachlorophenol caused unusual responses of the photosynthetic apparatus probably due to the especially high toxicity of this substance. Both cell shape and motility turned out to be insensitive physiological parameters for the toxicity testing of the substances studied.
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| 20. |
- Danilov, Roman, et al.
(author)
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Summer phytoplankton dynamics close to the shore in three brackish water bays on the East coast of Sweden (Gulf of Bothnia)
- 2000
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In: Thaiszia – J. Botany, Kosice. - 1210-0420. ; 9, s. 131-142
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Journal article (peer-reviewed)abstract
- Three brackish water bays between Härnösand and Sundsvall on the East coast of Sweden (Gulf of Bothnia) were investigated between June and August 1998 in order to reveal summer phytoplankton dynamics close to the coast. All samples were collected at depth of 0,5 m. The results obtained show patterns in phytoplankton dynamics. In the spring Bacillariophyceae dominated, followed by an increase in Dinophyceae and small flagellates of Prasinophyceae and Cryptophyceae. Chlorophyceae were represented during the whole period of investigation especially with species of Monoraphidium, which often dominated or subdominated. In total 84 phytoplankton species were identified. Cluster analyses based on similarities in species’ diversity and their abundance made it easy to distinguish between the bays close to Härnösand and the Bay of Sundsvall. However, no clear differences were found between the sampling stations within the Bay of Sundsvall.
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| 21. |
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| 22. |
- Danilov, Roman, et al.
(author)
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The use of epiphyton and epilithon data as a base for calculating ecological indices in monitoring of eutrophication in lakes in central Sweden
- 2000
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In: Science of the Total Environment. - 0048-9697 .- 1879-1026. ; 248, s. 63-70
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Journal article (peer-reviewed)abstract
- Eutrophication was monitored with the aid of one similarity and seven diversity indices in the lakes of different trophic levels (eutrophic, mesotrophic and oligotrophic) in central Sweden. The ecological indices were applied separately to epiphyton and epilithon communities. Epiphyton turned out to be inappropriate for assessing eutrophication in the lakes studied. On the other hand, Hurlbert's, Simpson's and the similarity indices turned out to be promising environmental tools when applied to the data of epilithon.
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| 23. |
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| 24. |
- Ekelund, Nils, 1956-, et al.
(author)
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Effects of autumnal stratification on phytoplankton communities in Lake Solumsjö, Sweden: Application of diversity indices and multivariate methods
- 2000
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In: Biologia. - 0006-3088 .- 1336-9563. ; 55:4, s. 357-362
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Journal article (peer-reviewed)abstract
- Effects of autumnal stratification on phytoplankton communities at different depths were studied in Lake Solumsjö, NE Sweden. Species number, Shannon-Weaver’s, Margalef’s and Menhinick’s indices as well as cluster analyses using presence-absence with abundance matrices were applied. All diversity indices used clearly indicated higher diversity in epilimnion compared to that in hypolimnion. This pattern can be explained by sole dominance of Trachelomonas volvocinopsis under predominantly anoxic conditions and high concentrations of iron and manganese below the thermal gradient. Stratification disappeared between September 29 and October 4, thus leading to homogenisation of water column and similar phytoplankton communities at all depths. Cluster analyses using presence-absence with abundance matrices turned out to be a powerful tool when studying temporal changes in phytoplankton communities as a result of stratification patterns. Two distinct clusters at depths of 0, 2 and 10 m were clearly separated: one containing algal communities during stratification and one containing algal communities after the thermal gradient disappeared. At the depth of 5 m more homogeny between phytoplankton communities under stratified and mixed conditions was observed.
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| 25. |
- Ekelund, Nils, et al.
(author)
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The influence of selenium on photosynthesis and light-enhanced dark respiration (LEDR) in the flagellate Euglena gracilis after exposure to ultraviolet radiation
- 2001
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In: Aquatic Sciences. - : Springer Science and Business Media LLC. - 1015-1621 .- 1420-9055. ; 63:4, s. 457-465
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Journal article (peer-reviewed)abstract
- Photodamage of photosynthesis arises from oxidative damage. One of the protective mechanisms is to convert excessive absorbed energy into thermal radiation. Another mechanism could be to strengthen the antioxidative capacity of plants and algae. Selenium is important in antioxidation in humans and may play a role in antioxidative mechanisms in plants. The aim of this investigation was to study the role of selenium in "light-enhanced dark respiration" (LEDR) and photosynthesis in the flagellate Euglena gracilis, after exposure to ultraviolet radiation (UV-radiation). Selenium was added into the growth medium at different concentrations of selenite (10-7, 10-8, 10-9 and 10-10 M, Na2SeO3 · 5H2O). E. gracilis were given six different light pulses with a photon fluence rate of 59, 163, 600, 1180, 2080 and 3340 μmol m-2 s-1 and periods of darkness between the light pulses. Photosynthetic saturation occurred at irradiances higher than 600 μmol m-2 s-1 and at the highest irradiance the photosynthetic rate decreased due to photoinhibition. Without any exposure to UV-radiation (UV-A, 320-400 nm, of 1.02 W m-2 plus UV-B, 280-320 nm, of 0.73 W m-2) LEDR increased with increasing photon fluence rate. After 40 min exposure to UV-radiation, photosynthetic rate and LEDR as functions of photon fluence rate were reduced. Neither in control (no UV-radiation) or when measured immediately after exposure to UV-radiation selenium had no stimulating effects on photosynthesis and LEDR. However, after UV-treatment and 24 h of recovery the presence of selenium led to an increase in photosynthesis and LEDR at higher irradiances. The results indicates that selenium might play a role in the repair mechanisms in E. gracilis after UV treatments.
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| 26. |
- Pystina, Natalia V., et al.
(author)
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Influence of light regimes on respiration, activity of alternative respiratory pathway and carbohydrates content in mature leaves of Ajuga reptans L.
- 2001
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In: Revista Brasileira de Fisiologia Vegetal. - 0103-3131. ; 13:3, s. 285-292
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Journal article (peer-reviewed)abstract
- Influence of different light regimes (plants grown in shade and in the sun) on respiration, activity of alternative respiratory pathway and carbohydrates content in mature leaves of Ajuga reptans L. was investigated. All experiments were carried out under natural conditions. Sun plants had higher respiration, activity of the alternative pathway and carbohydrates content compared to the shade plants. Additional experiments were performed in order to study effects of darkening as well as evolution of respiration and carbohydrates concentrations in leaves of A. reptans during the day. Darkening led to a decline in total respiration in all types of plants investigated. Activity of the alternative pathway remained unchanged by 20 % in the leaves of the shade plants. On the other hand, darkness led to a twofold decrease in the activity of the alternative pathway in the leaves of the sun plants. Content of soluble carbohydrates in the darkness did not change in the leaves of the shade plants while significantly decreased in the leaves of the sun plants. Total respiration in the mature leaves of the shade plants studied did not change significantly during the day. However, a significant increase in the total respiration was detected in the mature leaves of the sun plants in the evening and in the night. Activity of the alternative respiratory pathway did not change significantly in the leaves of the shade plants during the day and corresponds to ca 20 % of the total respiration. The sun plants examined exhibited significantly higher activity of the alternative pathway during the period of active photosynthesis. In general, activity of the alternative pathway varied in the sun plants between 30 and 35 % of the total respiration during the day. Content of soluble carbohydrates decreased significantly during the day in the mature leaves of the shade plants, while no statistically significant changes by the sun plants could be detected. It has been suggested that increase in respiration and activity of the alternative pathway in the sun plants tested can be controlled by the content of carbohydrates in leaves. No clear proposal could be done concerning mechanisms regulating alternative pathway activity in the shade plants of A. reptans.
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| 27. |
- Pystina, Natalia V., et al.
(author)
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Temperature-dependent alterations of respiration in leaves of two selected vascular plant species : The role of the alternative oxidase pathway
- 2002
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In: Bragantia. ; 61:2, s. 111-114
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Journal article (peer-reviewed)abstract
- Effects of higher temperatures on respiration and activity of alternative oxidase (AOX) were studied in mature leaves of Ajuga reptans L. and Rhodiola rosea L. Total respiration in both A. reptans and R. rosea increased exponentially with the increasing temperature of 10°C to 35°C. Respiration in the presence of benzhydroxamic acid (BHAM) also increased exponentially in accordance with the increasing temperature in the leaves of both A. reptans and R. rosea. Relative activity of the alternative pathway decreased significantly in the leaves of A. reptans with increasing temperatures. However, an increase in the relative activity of the alternative pathway was detected in the leaves of R. rosea. Thermoresistance of the alternative respiratory pathway was considered to be higher in R. rosea compared to A. reptans. We suppose that A. reptans and R. rosea have different mechanisms regulating partitioning of electrons to the alternative respiratory pathway.
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| 28. |
- Wahlström, G, et al.
(author)
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Phytoplankton successions under ice cover in four lakes located in North-Eastern Sweden: Effects of liming
- 2003
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In: Folia microbiologica (Prague). - 0015-5632 .- 1874-9356. ; 48:3, s. 379-384
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Journal article (peer-reviewed)abstract
- Phytoplankton successions under ice cover (January-March) were determined in four oligotrophic lakes (Burtjarn, Aspen, Vialamptjarn and Storkorstjarn) located in North-Eastern Sweden. The total phosphorus concentration in the lakes was less than 10 mug/L. Lake Burtjarn (reference lake) had a similar hydrology as Lake Aspen. Storkorstjarn and Vialamptjarn were of similar hydrology and had heavily colored water (>100 mg(Pt)/L). Aspen as well as Vialamptjarn became continuously limed with calcium carbonate annually during the last decades. Biodiversity was considerably higher in the limed lakes (Aspen and Vialamptjarn) than in the untreated lakes (Burtjarn and Storkorstjarn). In Lake Burtjarn the most frequent species were Rhodomonas lacustris, Tabellaria flocculosa and Botryococcus braunii. Cryptophyceae (R. lacustris and Cryptomonas marssonii) and Dinophyceae (especially Gymnodinium lantzschii) were common phytoplankton groups in Lake Aspen. Tabellaria flocculosa was also the most common organism in both humic lakes Storkorstjarn and Vialamptjarn, other phytoplankton groups were in the humic lakes scarce. Liming was found to have profound effects on phytoplankton communities studied.
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