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- Weich, R G, et al.
(författare)
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Extracellular alkaline phosphatase activity in Ulva lactuca L
- 1989
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Ingår i: Journal of Experimental Marine Biology and Ecology. - : Elsevier BV. - 0022-0981 .- 1879-1697. ; 129:1, s. 33-44
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Tidskriftsartikel (refereegranskat)abstract
- Extracellular alkaline phosphatase activity (APA) was detected in the marine macroalga Ulva lactuca, cultivated in laboratory conditions under phosphate limitation. Algal discs were grown in continuous light and in darkness for a maximum of 205 h in sterilized seawater supplied with ammonium nitrate and various phosphate concentrations. APA and phosphate uptake in U. lactuca was stimulated in light whereas inhibition was detected in darkness. APA increased significantly during the cultivation in a phosphate-deficient medium but was suppressed at high external phosphate concentrations. In addition, pretreatment in penicillin over 48 h markedly enhanced enzyme activity during P limitation. The pretreatment in penicillin reduced the number of surface-associated bacteria. Our results indicate that APA in U. lactuca was dependent on the external phosphate concentration, energy from photophosphorylation and bacteria. Since intracellular polyphosphates and an orthophosphate pool still were displayed in 31P NMR spectra after cultivation at phosphate-limiting conditions, P deficiency was not suggested. Unfortunately, NMR spectra reflect total amounts of P compounds and local differences in the P status of the multicellular tissue could not be distinguished. Postulating a negative correlation between the P status and APA, a lower P status in meristematic areas during P limitation was suggested. Alkalisation of the growth medium during algal growth in light, and/or intracellular pH changes may additionally have affected enzyme production.
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| 2. |
- Granéli, Edna, et al.
(författare)
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The response of planktonic and microbenthic algal assemblages to nutrient enrichment in shallow coastal waters, Southwest Sweden
- 1985
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Ingår i: Journal of Experimental Marine Biology and Ecology. - : Elsevier BV. - 0022-0981 .- 1879-1697. ; 85:3, s. 253-268
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Tidskriftsartikel (refereegranskat)abstract
- Field and laboratory nutrient (nitrogen and phosphorus) enrichment experiments were performed using natural phytoplankton and microphytobenthic assemblages from the brackish water Öresund, S.W. Sweden. The response of algae from a low-nutrient area (Falsterbo Canal) was compared to that of algae from a polluted, nutrient-rich area (Lomma Bay).The biomass (measured as chlorophyll a) of both phytoplankton and microphytobenthos from the Falsterbo Canal increased after the addition of nitrogen. Phytoplankton growth was stimulated by the addition of phosphorus to the nitrogen-rich water of the polluted Lomma Bay. Sediment chlorophyll a showed no significant increase after the addition of nutrients in the Lomma Bay. In containers without sediment, phytoplankton uptake was calculated to account for ≈ 90% of the disappearance of inorganic fixed nitrogen from the water. In the sediment containers the microphytobenthos was estimated to account for ≈20% of the nitrogen uptake. The rest was presumably lost mainly through denitrification.When containers with microphytobenthos from Lomma Bay were kept in the dark, phosphorus was released at a rate of up to ≈ 180 μM · m−2 · day−1. We suggest that by producing oxygen microbenthic algae keep the sediment surface oxygenated thereby decreasing phosphorus transport from the sediment to the overlying water.
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