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  • 1.
    Ekelund, N. G. A.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Interactions between photosynthesis and 'light-enhanced dark respiration' (LEDR) in the flagellate Euglena gracilis after irradiation with ultraviolet radiation2000Ingår i: Journal of Photochemistry and Photobiology. B: Biology, ISSN 1011-1344, E-ISSN 1873-2682, Vol. 55, nr 1, s. 63-69Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effects of ultraviolet radiation (UV-A, 315-400 nm plus UV-B, 280-315 nm) on photosynthesis and 'light-enhanced dark respiration' (LEDR) in Euglena gracilis have been investigated by using light pulses (80 s) with increasing photon fluence rates of 59, 163, 600, 1180, 2080 and 3340 mu mol m(-2) s(-1) and dark periods between the light pulses. LEDR is estimated as the maximum rate of oxygen consumption after a period of Light minus the rate of oxygen consumption 30 s after the maximum rate. Without any exposure to UV radiation, the photosynthetic rate and LEDR increase with increasing photon fluence rate. After 20 and 40 min exposures to UV radiation, the photosynthetic rate and LEDR as functions of photon fluence rate are reduced. After a 20 min UV treatment respiration is greater than photosynthesis after the first light pulse of 59 mu mol m(-2) s(-1) radiation, and especially at higher photon fluence rates photosynthesis is lower than the control values. The inhibitory effects of UV radiation on photosynthetic rate and LEDR are greater after a 40 min UV exposure than after a 20 min exposure. Only at 600 mu mol m(-2) s(-1) is the rate of oxygen evolution greater than that of oxygen consumption after a 40 min UV treatment. Both photosynthetic rate and LEDR are inhibited by the photosynthetic inhibitor DCMU (10(-5) M) in a similar way, which indicates close regulatory interactions between photosynthesis and LEDR. Potassium cyanide (KCN) inhibits dark respiration more than it inhibits LEDR. Dark respiration is not affected to the same degree by UV radiation as are photosynthesis and LEDR.

  • 2. Figueroa, Felix
    et al.
    Nygård, Charlotta
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Ekelund, Nils
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Gomez, Ivan
    Photobiological characteristics and photosynthetic UV responses in two Ulva species (Chlorophyta) from southern Spain.2003Ingår i: Journal of Photochemistry and Photobiology. B: Biology, ISSN 1011-1344, E-ISSN 1873-2682, Vol. 72, nr 1-3, s. 35-44Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effect of different wavebands of artificial UV (UVB and UVA) and photosynthetically active radiation (PAR) was assessed in two species of the genus Ova, U. olivascens and U rotundata, from southern Spain in order to test for possible differences in acclimation of photosynthesis. Both species share similar morphology but are subject to different light environments: U. rotundata is an estuarine alga, inhabiting subtidal locations, while U. olivascens is an intertidal, sun-adapted organism. Algae were exposed to three different UV conditions, PAR + UVA + UVB, PAR + UVA and PAR for 7 d. Short-term exposure (6 h) was also carried out, using two PAR levels, 150 and 700 mumol m(-2) s(-1). Pigment contents and photosynthesis vs. irradiance curves from oxygen evolution were used to contrast sun- and shade adaptation between these species. O-2-based net photosynthesis (P-max) and PAM-chlorophyll fluorescence (optimal quantum yield, F-v/F-m) were used as parameters to evaluate photoinhibition of photosynthesis in the experiments. The results underline different photobiological characteristics among species: the subtidal U rotundata had higher contents of pigments (Chl a, Chl b and carotenoids) than the sun-adapted U olivascens, which resulted in higher thallus absorptance and P-I parameters characterized by higher photosynthetic efficiency at limiting irradiances (alpha) and lower saturating points for photosynthesis (E-k). After 7 d exposure, photoinhibition of F-v/F-m was close to 40-45% in both species. Differences between UV treatments were seen in U. rotundata after 5 0 and after 7 d in U olivascens, in which PAR + UVA impaired strongly photosynthesis (80%). Such patterns were correlated with a progressive decrease in pigment contents, specially chlorophylls. In short-term (6 h) exposures, combinations of UVA + UVB and high PAR level resulted in high rates of photoinhibition of chlorophyll fluorescence (68-92%) in U rotundata, whereas in U. olivascens photoinhibition ranged between 42% and 53%. Photoinhibition under low PAR combined to UV radiation was lower than observed under high PAR. Net O-2-P-max revealed similar response among the species, with maximal photoinhibition rates close to 60% in algae incubated under high PAR + UVA + UVB. In the case of UV exposure in combination with low PAR, the highest photoinhibition rates were measured in U. rotundata. 

  • 3. Nielsen, Tom
    et al.
    Björn, Lars Olof
    Ekelund, Nils
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Impact of natural and artificial ultraviolet-B radiation on motility and growth rate of marine dinoflagellates1995Ingår i: Journal of Photochemistry and Photobiology. B: Biology, ISSN 1011-1344, E-ISSN 1873-2682, Vol. 27, s. 73-79Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The growth rates and motility of dinoflagellates were studied in the field in the presence or absence of UVB radiation, as well as in the laboratory under artificial radiation conditions. Photosynthetically active radiation (PAR, 400–700 nm) and UVB radiation showed large variations due to cloud cover and seasonal changes in natural daylight. In Swedish coastal water, UVB radiation was attenuated to about 10% of surface irradiance at a depth of 120 cm. There was no significant difference in the motility of two strains of Prorocentrum minimum (Atlantic, LAC4LI; Kattegat, LAC6KA83) kept in the water at different depths (35 and 120 cm) for 4 h, with or without natural solar UV radiation, except for a day with high UVB irradiance (1.2 W m−2), which decreased the motility at a depth of 35 cm for the two species). Simulated in situ experiments with 2 h natural daylight, with and without natural UV radiation (UVB, 1.6 W m−2), had a dramatic effect on the motility of Gyrodinium aureolum. Artificial UVB radiation from UV lamps (4 h, 2.72 kJ m−2 day−1, biologically effective UVB radiation, UVBBE) in the laboratory decreased the motility of Heterocapsa triquetra (LAC20) by 56% and the two strains of P. minimum (Atlantic, LAC4LI; Kattegat, LAC6KA83) by 43% and 36% respectively; the growth was inhibited for all species, as well as for Amphidinium carterae (LAC1KA83), when organisms were exposed to more than 0.7 kJ m−2 day−1 of UVBBE radiation.

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