| 1. |
- Braune, Wolfram, et al.
(författare)
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Phototactic responses in Haematococcus lacustris and its modification by light intensity and the carotenoid biosynthesis inhibitor Norflurazon
- 1990
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Ingår i: Archives of Microbiology. - 0302-8933 .- 1432-072X. ; 154, s. 448-452
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Tidskriftsartikel (refereegranskat)abstract
- At fluence rates below 45 W· m-2 cells of the flagellate stage of Haematococcus lacustris react only positively phototactically with a rather high degree of orientation (indicated by r values up to 0.66 with the Rayleigh test). The directedness of orientation decreases with decreasing irradiance. The degree of directedness of the phototactic response depends on the intensity of preirradiation: Low light intensity applied after strong light application results in a dark reaction (low r values), low light given after darkness stimulates a rather high degree of directedness of positive phototaxis. Weak blue light (=483 nm; 0.4 W · m-2) stimulates positive phototactic response, whereas comparable red light (=658 nm; 0.5 W · m-2) does not. Cells which were grown in a medium containing 10-4 M Norflurazon (effective in inhibition of carotenoid biosynthesis) although maintaining motility completely lose the ability to react positively phototactically. The possible role of carotenoids in the phototactic orientation is discussed.
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| 2. |
- Ekelund, Nils, 1956-
(författare)
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Effects of UV-B radiation on growth and motility of four phytoplankton species
- 1990
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 78, s. 590-594
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Tidskriftsartikel (refereegranskat)abstract
- A depletion of the stratospheric ozone layer would result in an increased UV-B radiation, which could have harmful effects on marine organisms. The aim of this study was to determine the effects of an enhanced UV-B radiation (280–320 nin) on the motility and growth in four Swedish phytoplanklon species. The different plankton species were exposed to different doses of UV-B radiation during growth. The growth of the motile dinoflagellates, Gyronidium aureolum Hulburt (Ba 6), and Prorocentrum minimum (Pav.) P. Schiller (Ba 12), was more sensitive to UV-B radiation than the non-motile diatoms Dityhim brightwellii (P. West) Grun (Ba 15) and Phaeodactylum tricornutum Bohlin (Ba 16). One week of UV-B radiation 2 h daily (159 J m−2 day−1), had a dramatic effect on the growth of the dinoflagellates, while the diatoms were nearly unaffected. On the other hand, when given higher intensity of UV-B radiation (312, 468 and 624 J m−2 day−1) during the initial phase of growth, also the growth of the diatom, D. brightwellii, was inhibited. Not only the growth but also the swimming speed of the dinoflagellates C. aureolum and P. minimum were affected by UV-B radiation. The speed decreased rapidly after 1–2 h of UV-B radiation (312 J m−2 day−1), and after longer irradiation times the dinoflagellates lost their motility. G. aureolum exposed to UV-B radiation, regained normal speed after two weeks of visible light.
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| 3. |
- Ekelund, Nils, 1956-
(författare)
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Studies on the effects of UV-B radiation on phytoplankton of Sub-Antarctic lakes and ponds
- 1992
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Ingår i: Polar Biology. - 0722-4060 .- 1432-2056. ; 12, s. 533-537
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Tidskriftsartikel (refereegranskat)abstract
- Experiments were performed to determine the effects of UV-B (ultraviolet, 280–320 nm) radiation on motility and growth of phytoplankton from lakes and ponds in South Georgia. After 4 h of solar radiation and 4h artificial radiation (UV-BBE 11.6 kJ m-2 day-1, UV-B lamps) the swimming velocity of Cryptomonas sp. decreased. The growth rate of Botryococcus, Lyngbya sp. and Stauraslrum sp. did not show any significant variations between the different light conditions. The UV-B component was reduced by filtering solar radiation through glass bottles und cellulose acetate. Cloudy days had only 30% of the radiation of clear days in both the PAR (photosynthetic active radiation) and UV-B regions. The ponds contained large amounts of humic substances, which are responsible for the absorbance in the UV region.
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| 4. |
- Ekelund, Nils, 1956-
(författare)
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The effect of UV-B radiation and humic substances on growth and motility of the flagellate, Euglena gracilis.
- 1993
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Ingår i: Journal of Plankton Research. - : Oxford University Press (OUP). - 0142-7873 .- 1464-3774. ; 15, s. 715-722
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Tidskriftsartikel (refereegranskat)abstract
- The effects of ultraviolet-B radiation (UV-B, 250–315 nm) were determined on Euglena gracilis with respect to speed, phototactic orientation, specific growth rate, and in the presence of humic substances. Humic substances had a protective effect when studying the speed and specific growth rate. However, the degree of phototactic orientation decreased in UV-B radiation both with and without humic substances. The inhibition of O2 evolution and speed was most pronounced when using cutoff filters WG280 and WG295. The photosynthetic inhibitor DCMU (10–6 M) did not have any effect on the speed, but the 02 evolution decreased to zero. The effect of different wavelengths in the UV-B region on the speed of E.gracilis showed the maximum sensitivity at 280 and 290 nm.
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| 5. |
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| 6. |
- Petersen-Mahrt, Silja, et al.
(författare)
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Influence of UV-B radiation and nitrogen starvation on daily rhythms of phototaxis and cell shape in Euglena gracilis
- 1994
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 92:3, s. 501-505
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Tidskriftsartikel (refereegranskat)abstract
- The flagellate Euglena gracilis Klebs strain Z shows phototaxis and changes cell shape between oblong and round. Both cell events show daily rhythmicity. Phototaxis was highest about 2 h after light onset with a second peak of activity 9 h later. At the same times, the cells were in their most oblong shape. During the night phase the cells were phototactically inactive and round. These rhythms were altered by environmental stress, e.g. UV-B radiation (280–320 nm) and nitrogen deficiency. Artificial UV-B radiation of 0.5 W m−2 caused a loss in phototaxis hut the peak of activity occurred at the same time as for control cells. The transition from round to oblong cell shape was slower after UV-B radiation, but the difference between the roundest and the most oblong cell shape was unchanged. Nitrogen deficiency caused a total loss of phototaxis and the cells remained round all the time. The cells lost all their chlorophyll and were, therefore, photosynthetically inactive.
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| 7. |
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| 8. |
- Ekelund, Nils, 1956-
(författare)
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Influence of UV-B radiation on light-response curves, absorption spectra and motility of four phytoplankton species
- 1994
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 91, s. 696-702
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Tidskriftsartikel (refereegranskat)abstract
- Several unicellular algae were exposed to artificial UV‐B (280–320 nm) radiation after adaptation to high (43 W m−2) and low (19 W m−2) visible light. UV‐B radiation had different effects on rates of photosynthesis, motility and absorption spectra for these species. Photosynthesis of Euglena gracilis and the diatom Phaeodactylum tricomution was more sensitive to UV‐B inhibition than that of the dinoflagellates Heterocapsa triquetra and Prorocentrum minimum. Not only UV‐B radiation but also high visible light had a photoinhibitory effect on photosynthesis in all four organisms. The effect on photosynthesis was observed both on the quantum yield and on the light saturation rate of photosynthesis. The dinoflagellates, in contrast to E. gracilis and P. tricorntum, absorbed strongly in the UV region (334 nm) and their absorption peaks increased after growth under high visible light or with or without UV‐B radiation for one week. The swimming speed of H. triquetra decreased more after low visible light and UV‐B radiation compared to high visible light and UV‐B radiation. The negative effects of UV‐B radiation on P. minimum and E. gracilis were most pronounced after high visible light.
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| 9. |
- Ekelund, Nils, 1956-
(författare)
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The effects of UV-B radiation on dinoflagellates
- 1991
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Ingår i: Journal of plant physiology (Print). - 0176-1617 .- 1618-1328. ; 138, s. 274-278
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Tidskriftsartikel (refereegranskat)abstract
- Ultraviolet radiation, UV-B (280-320 nm), has harmful effects on marine phytoplankton. The presentexperiments were done to determine the effects of UV-B radiation on motility and growth of four marine motile dinoflagellates, Gyrodinium aureolum, Prorocentrum minimum, Heterocapsa triquetra and Scrippsiella trochoidea. The specific growth rate of the dinoflagellates showed an inhibition after 1 hour UV-B (1.5 kj m(su-2}day-1) daily during 1 week. The motility of H. triquetra showed a pronounced inhibition after 12 kJ m-2day-1, the motility of S. trochoidea did not show the same sensitivity to UV-B radiation. The photosynthetic inhibitor DCMU (10-5M) inhibited the motility of S. trochoidea but not the motility of H. triquetra. Action spectra (UV-B, 280-320 nm) for inhibition of motility of G. aureolum showed the maximum sensitivity at 280 and 290 nm.
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| 10. |
- Helitzer-Allen, Deborah, et al.
(författare)
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Obtaining sensitive information : The need for more than focus groups
- 1994
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Ingår i: Reproductive health matters. - : Informa UK Limited. - 0968-8080 .- 1460-9576. ; 2:3, s. 75-82
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Tidskriftsartikel (refereegranskat)abstract
- Pour les recherches sur la santé reproductive, on utilise de plus en plus des méthodes de recherche qualitative telles qu'entretiens approfondis, discussions de groupe en profondeur et observation des participantes afin d'améliorer l'information obtenue à partir des méthodes plus classiques de recueil de données. Cet exposé étaye des résultats tirés de deux méthodes de recherche qualitative différentes parmi une population de jeunes adolescentes en zone rurale au Malawi. Il fournit l'évidence concrète que se fier uniquement à une information obtenue par l'intermédiaire de discussions de groupe en profondeur est insuffisant pour comprendre le contexte cultural et les normes sociales au sein desquels les jeunes femmes découvrent la reproduction et la sexualité. Ces résultats font ressortir le rapport entre les réponses données et la méthodologie utilisée. En outre, ils soulèvent des questions sur la façon de diffuser une information délicate aux jeunes filles afin de les aider à évitar une grossesse non désirée et les infections transmises sexuellement.
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