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Many brown algae, including the kelp Laminaria digitata (Huds.) Lamour., exhibit enhanced photosynthesis when they are given a small amount of blue-light in addition to a background of saturating red light. This blue light effect is correlated with an increased uptake of carbon. In the present study, we tested the hypothesis that blue light acts by increasing the activity of a plasma membrane H+ -ATPase, thereby promoting an active carbon uptake across the plasma membrane. Photosynthetic carbon uptake was studied in pH-drift experiments under illumination with red and blue light and using different inhibitors. Vanadate, an inhibitor of plasma membrane H+ -ATPases, had a minor inhibitory effect on carbon uptake rates under saturating red light conditions, but inhibited the blue-light enhancement by approximately 60%. An inhibitor of external carbonic anhydrase, acetazolamide, decreased the carbon uptake in both red light and in red plus blue light by 48% and 68%, respectively. These results suggest that photosynthetic carbon uptake depends on an external carbonic anhydrase under both red and red plus blue light conditions, and that blue light induces an increased activity of a P-type H+ -ATPase in the plasma membrane. The proton buffer Tris, which has a buffering capacity similar to vanadate in seawater, had no inhibitory effect on carbon uptake rates neither in red light nor in red plus blue light, showing that the inhibitory effect of vanadate is not caused by its effect as a buffer. The blue-light enhancement was also abolished by a protein kinase inhibitor (H-7), suggesting that the transduction of the blue-light signal involves a protein kinase, which activates the plasma membrane H+ -ATPase by phosphorylation. [ABSTRACT FROM AUTHOR]

Carbon uptake in the green macroalga Cladophora glomerata (L.) Kütz. from the brackish Baltic Sea was studied by recording changes in pH, alkalinity, and inorganic carbon concentration of the seawater medium during photosynthesis. The use of specific inhibitors identified three uptake mechanisms: 1) dehydration of HCO3 - into CO2 by periplasmic carbonic anhydrase, followed by diffusion of CO2 into the cell; 2) direct uptake of HCO3 - via a 4,4′-diisothiocyanato-stilbene-2,2′-disulfonate-sensitive mechanism; and 3) uptake of inorganic carbon by the involvement of a vanadate-sensitive P-type H+ -ATPase (proton pump). A decrease in the alkalinity of the seawater medium during carbon uptake, except when treated with vanadate, indicated a net uptake of the ionic species contributing to alkalinity (i.e. HCO3 - , CO3 2- , and OH- ) from the medium, where OH- influx is equivalent to H+ efflux. This would suggest that the proton pump is involved in HCO3 - transport. We also show that the proton pump can be induced by carbon limitation. The inducibility of carbon uptake in C. glomerata may partly explain why this species is so successful in the upper littoral zone of the Baltic Sea. Usually, carbon limitation is not a problem in the upper littoral of the sea. However, it may occur frequently within dense Cladophora belts with high photosynthetic rates that create high pH and low carbon concentrations in the alga's microenvironment. [ABSTRACT FROM AUTHOR]

The rate of oxygen evolution of the tropical red alga Kappaphycus alvarezii (Doty) Doty was measured for 6 days in the laboratory using a computer-aided method for long-term recording. In cool white light, Kappaphycus exhibited a robust circadian rhythm of O2 evolution in the irradiance range of 100 to 1000 μmol photons·m-2·s-1. With increasing irradiance, the period of the free-running rhythm, τ, decreased in blue and increased in red light but did not change significantly in green light. The accelerating or slowing action of blue or red light, respectively, points to two photoreceptors used in the light transduction pathway of the circadian oscillator controlling oxygen evolution or the light reactions of photosynthesis in Kappaphycus. No significant changes of τ were observed with increasing irradiance in cool white light, possibly due to the additive opposing responses caused by blue and red light. [ABSTRACT FROM AUTHOR]

The enzyme α-1,4-glucan lyase (EC 4.2.2.13) was studied in cells of young and mature parts of the red alga Gracilariopsis sp. by using immunogold labeling in ultrastructural studies. In young tissues, the α-1,4-glucan lyase was observed at two different sites: around the starch granules in the cytosol and in the stroma of the chloroplast. In mature tissues, the α-1,4-glucan lyase was present only in the chloroplasts. The possible role of this starch-degrading enzyme in red algae is discussed. [ABSTRACT FROM AUTHOR]

The cuticles and chloroplasts of young and old fronds of Polysiphonia nigrescens (Huds.) Grev. were analysed by quantitative X-ray microanalysis for their content of bromine. Cuticles of old fronds contained 1.7 ± 0.14% bromine while those of young ones contained only 0.94 ± 0.22% bromine. The bromine content of the chloroplasts showed considerable variations between individual chloroplasts, but was found not to increase with age. Young fronds contained four separate layers in the cuticle when observed under the electron microscope. In the old fronds three of these layers disappeared while the remaining one became thick and very electron dense. [ABSTRACT FROM AUTHOR]

Thalli of Ulva reticulata Forskaal, Ulva rigida C. Ag., and Ulva pulchra Jaasund were incubated at different concentrations of dissolved CO[SUB2]. Incubation at a high CO[SUB2]2 concentration resulted in decreased oxygen evolution rate and lower affinity for inorganic carbon at high pH conditions, i.e. the ability to use HCO[SUP-][SUB3] as a carbon source was reduced. This effect was reversible, and plants regained this HCO[SUP-][SUB3] uptake capacity when transferred to air concentrations of CO[SUB2] The phytosynthetic oxygen evolution rate of plants grown at high C02 concentration was reduced by high O[SUB2] concentrations, whereas thalli and protoplasts from cultures grown at air concentration were not affected. This is interpreted as a deactivation of the carbon-concentrating mechanism during conditions of high CO[SUB2] resulting in high photorespiration when plants are exposed to high O[SUB2] concentrations. Protoplasts were not affected by high O[SUB2] to the same extent and were not able to utilize HCO[SUP-][SUB3] from the medium. The algae were able to grow at very low CO[SUB2] concentrations, but growth was suppressed when ah inhibitor of external carbonic anhydrase was present. Assay of carbonic anhydrase activities showed that external and internal CA activities were lower in plants grown at a high CO[SUB2] concentration compared to plants grown at a low concentration of CO[SUB2] possible mechanisms for HCO[SUP-][SUB3] utilization in these Ulva species are discussed. [ABSTRACT FROM AUTHOR]

Many brown algae, including the kelp Laminaria digitata (Huds.) Lamour., exhibit enhanced photosynthesis when they are given a small amount of blue-light in addition to a background of saturating red light. This blue light effect is correlated with an increased uptake of carbon. In the present study, we tested the hypothesis that blue light acts by increasing the activity of a plasma membrane H+ -ATPase, thereby promoting an active carbon uptake across the plasma membrane. Photosynthetic carbon uptake was studied in pH-drift experiments under illumination with red and blue light and using different inhibitors. Vanadate, an inhibitor of plasma membrane H+ -ATPases, had a minor inhibitory effect on carbon uptake rates under saturating red light conditions, but inhibited the blue-light enhancement by approximately 60%. An inhibitor of external carbonic anhydrase, acetazolamide, decreased the carbon uptake in both red light and in red plus blue light by 48% and 68%, respectively. These results suggest that photosynthetic carbon uptake depends on an external carbonic anhydrase under both red and red plus blue light conditions, and that blue light induces an increased activity of a P-type H+ -ATPase in the plasma membrane. The proton buffer Tris, which has a buffering capacity similar to vanadate in seawater, had no inhibitory effect on carbon uptake rates neither in red light nor in red plus blue light, showing that the inhibitory effect of vanadate is not caused by its effect as a buffer. The blue-light enhancement was also abolished by a protein kinase inhibitor (H-7), suggesting that the transduction of the blue-light signal involves a protein kinase, which activates the plasma membrane H+ -ATPase by phosphorylation. [ABSTRACT FROM AUTHOR]

Carbon uptake in the green macroalga Cladophora glomerata (L.) Kütz. from the brackish Baltic Sea was studied by recording changes in pH, alkalinity, and inorganic carbon concentration of the seawater medium during photosynthesis. The use of specific inhibitors identified three uptake mechanisms: 1) dehydration of HCO3 - into CO2 by periplasmic carbonic anhydrase, followed by diffusion of CO2 into the cell; 2) direct uptake of HCO3 - via a 4,4′-diisothiocyanato-stilbene-2,2′-disulfonate-sensitive mechanism; and 3) uptake of inorganic carbon by the involvement of a vanadate-sensitive P-type H+ -ATPase (proton pump). A decrease in the alkalinity of the seawater medium during carbon uptake, except when treated with vanadate, indicated a net uptake of the ionic species contributing to alkalinity (i.e. HCO3 - , CO3 2- , and OH- ) from the medium, where OH- influx is equivalent to H+ efflux. This would suggest that the proton pump is involved in HCO3 - transport. We also show that the proton pump can be induced by carbon limitation. The inducibility of carbon uptake in C. glomerata may partly explain why this species is so successful in the upper littoral zone of the Baltic Sea. Usually, carbon limitation is not a problem in the upper littoral of the sea. However, it may occur frequently within dense Cladophora belts with high photosynthetic rates that create high pH and low carbon concentrations in the alga's microenvironment. [ABSTRACT FROM AUTHOR]