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  • 1. Björn, Gunvor
    et al.
    Ekelund, Nils
    Björn, Lars Olof
    Light-induced lineardichroism in photoreversibly photochromic sensor pigments.” - IV. Lack of chromophore rotation in phycochrome b immobilized in vitro1984In: Physiologia Plantarum: An International Journal for Plant Biology, ISSN 0031-9317, E-ISSN 1399-3054, no 60, p. 253-256Article in journal (Refereed)
  • 2.
    Ekelund, Nils
    Dept of Plant Physiology, Lund Univ..
    Effects of UV-B radiation on growth and motility of four phytoplankton species1990In: Physiologia Plantarum: An International Journal for Plant Biology, ISSN 0031-9317, E-ISSN 1399-3054, Vol. 78, p. 590-594Article in journal (Refereed)
    Abstract [en]

    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.

  • 3.
    Ekelund, Nils
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Influence of UV-B radiation on light-response curves, absorption spectra and motility of four phytoplankton species1994In: Physiologia Plantarum: An International Journal for Plant Biology, ISSN 0031-9317, E-ISSN 1399-3054, Vol. 91, p. 696-702Article in journal (Refereed)
    Abstract [en]

    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 tricornum was more sensitive to UV-B inhibition than that of the dinoflagellates Heterocapsa triquetra and Prorocentrum minimum. Not only UV-B radiation but 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

  • 4.
    Ekelund, Nils
    et al.
    Dept of Plant Physiology, Univ. of Lund.
    Björn, Lars Olof
    Photophobic stop-response in a dinoflagellate: Modulation by preirradiation1987In: Physiologia Plantarum: An International Journal for Plant Biology, ISSN 0031-9317, E-ISSN 1399-3054, Vol. 70, p. 394-398Article in journal (Refereed)
  • 5.
    Ekelund, Nils
    et al.
    Dept of Plant Physiology, Univ. of Lund.
    Dolle, Rainer
    Nultsch, Wolfgang
    Phototactic responses of Chlamydomonas reinhardtii in electric fields1988In: Physiologia Plantarum: An International Journal for Plant Biology, ISSN 0031-9317, E-ISSN 1399-3054, Vol. 73, p. 265-270Article in journal (Refereed)
    Abstract [en]

    Chlamydomonas reinhardtii Dangeard strain Göttingen 11 – 32(+) responds both phototactically and galvanotactically. If electric fields and a light stimulus of 496 nm were applied simultaneously, phototaxis persisted but the response was modified. Field lines perpendicular to the phototactic direction of movement inhibited phototaxis. If the field lines were parallel to the light direction, the effect depended on the position of the poles. When the cathode faced the light, an increase of the phototactic reaction values was observed. In this case electric fields enhanced positive phototaxis with increasing voltages from 3 V up to 12 V. If the cathode was on the opposite side, positive phototactic movement was inhibited. The maximum inhibition was found at 12 V. At this voltage positive phototaxis was measured neither at low nor at high fluence rates, and positive phototaxis was shown only between 0.1 and 1.5 W m−1.

  • 6. Petersen-Mahrt, Silja
    et al.
    Ekelund, Nils
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Widell, Susanne
    Effects of UV-B radiation and nitrogen starvation on enzyme activities in isolated plasma membranes of Euglena gracilis1995In: Physiologia Plantarum: An International Journal for Plant Biology, ISSN 0031-9317, E-ISSN 1399-3054, Vol. 95, p. 515-522Article in journal (Refereed)
    Abstract [en]

    Circadian rhythms are characteristic of many physiological and biochemical processes in the freshwater flagellate Euglena gracilis. Earlier, we found that the rhythms of photosynthesis, phototaxis and cell shape followed the same pattern in control organisms, but were differently affected by stress such as UV-B irradiation and nitrogen deficiency. Here we extend our studies to use isolated plasma membranes to characterize the rhythms of some plasma membrane-bound enzymes. Also, we wanted to see whether stress-induced changes of these rhythms could be detected at the subcellular level and possibly be coupled to the changes seen in photosynthesis, phototaxis and cell shape. The isolation of plasma membranes using aqueous polymer two-phase partitioning was successful, as judged by the large enrichment of the plasma membrane-marker 5'-nucleotidase, and the difference in the polypeptide pattern compared with the microsomal fraction from which it was prepared. Two other enzymes were analyzed, K+,Mg2+-ATPase, and adenylyl cyclase. The specific activities of all three enzymes were decreased by UV-B radiation by ca 30-50%, compared with the control cultures. On the other hand, nitrogen deficiency not only reduced the activity of the K+,Mg2+-ATPase but also increased the activities of the 5'-nucleotidase and adenylyl cyclase. The different treatments also resulted in differences in polypeptide pattern, e.g., a polypeptide around 30 kDa seemed to be specific to plasma membranes of nitrogen-deficient cultures and one at 39 kDa for the UV-B radiated ones. All three enzymes showed diurnal rhythms that were affected by UV-B radiation. The peak in the rhythm of the ATPase was shifted by UV-B radiation, the rhythm of the 5'-nucleotidase nearly eliminated. The first peak of adenylyl cyclase activity was delayed, so that it looked more like a broad peak between 2 and 11 h after the onset of light. The rhythm of ATPase activity could be correlated with that of photosynthesis in both control and UV-B irradiated cultures. Also, the rhythms of adenylyl cyclase activity and cell shape changes showed some similarities.

  • 7. Petersen-Mahrt, Silja
    et al.
    Ekelund, Nils
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Widell, Susanne
    Influence of UV-B radiation and nitrogen starvation on daily rhythms of phototaxis and cell shape in Euglena gracilis1994In: Physiologia Plantarum: An International Journal for Plant Biology, ISSN 0031-9317, E-ISSN 1399-3054, Vol. 92, no 3, p. 501-505Article in journal (Refereed)
    Abstract [en]

    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.

  • 8. Sundqvist, Christer
    et al.
    Ekelund, Nils
    Dept of Plant Physiology, Univ. of Lund.
    Spectral properties and chromophore rotation of phytochrome bound to substituted Sepharose1986In: Physiologia Plantarum: An International Journal for Plant Biology, ISSN 0031-9317, E-ISSN 1399-3054, Vol. 66, p. 185-190Article in journal (Refereed)
    Abstract [en]

    Brushite purified phytochrome from Avena sativa L. cv. Sol II was bound to phenyl Sepharose, octyl Sepharose, CNBr-activated Sepharose and to anti-phytochrome immunoglobulins immobilized on Sepharose. The spectral properties of phytochrome bound to anti-phytochrome immunoglobulins and to phenyl Sepharose were similar to phytochrome in solution. Phytochrome bound to CNBr-activated Sepharose or to octyl Sepharose showed reduced Pfr formation after red irradiation. The reversal to Pr with far-red light was only partial but a further increase at 667 nm took place slowly in the dark. A peak at 657 nm was seen in the difference spectrum between CNBr-activated Sepharose-bound phytochrome kept in darkness and the identical sample immediately after a far-red irradiation.

    The change in linear dichroism at 660 nm and 730 nm, induced by plane polarized red or far-red light, was measured. It was computed that the long-wavelength transition moment of phytochrome had an average rotation angle of 31.5° or 180°–31.5°. The substrate used for immobilization had a limited effect on the rotation angle. Phytochrome immobilized on CNBr-activated Sepharose gave an angle of 27.8° and phytochrome immobilized on phenyl Sepharose gave an angle of 32.6°.

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