ALBERT

Notes: Abstract In 1987 effects of salinity fluctuations on growth of the centric diatom Skeletonema costatum (Greville) Cleve, isolated from the brackish Krammer estuary (SW Netherlands) in 1981, were investigated. Continuous cultures (12 h light: dark cycle) of S. costatum were adapted to constant salinity in natural (16.1‰) and synthetic (13.5‰) media. For several days the ammonium-limited cultures were exposed to a salinity fluctuation (minimum 4.8‰). Decreasing salinity caused an inhibition of photosynthesis, dark respiration and cell growth. Cellular pools of glucose decreased. While the carbohydrate content remained constant, the protein content increased slightly. Net carbon fixation was more inhibited than nitrogen assimilation. Ammonium accumulated during a salinity decrease; a total decline of the overcapacity of ammonium uptake was noticed and nitrogen limitation was relieved. Amino acid pools decreased, probably as a result of excretion (osmoregulation). The enzymes invoilved in ammonium assimilation showed an increased activity. Cellular activities were resumed during a salinity increase. Chlorophyll a increased; photosynthesis, ammonium uptake and growth were stimulated. The ammonium uptake capacity recovered completely; glutamic acid accumulation and increased glutamate-dehydrogenase (GDH) activity indicated supplementary ammonium assimilation via GDH. The activities of glutamine synthetase/glutamate synthase (GS/GOGAT) and GDH stabilized, and the cells returned to steady state under ammonium limitation.

Notes: [Auszug] Batch cultures of the strain were maintained on an orbital shaker at 20 C in a mineral medium5 at a photon-flux density of 30 jxE m2 s"1 (warm, white fluorescent lamps) and an alter-nating light/dark regime of 16 h: 8 h. The strain was character-ized by pigment analysis, electron microscopy and ...

Notes: Abstract The field of photobiology is concerned with the interactions between light and living matter. For Bacteria this interaction serves three recognisable physiological functions: provision of energy, protection against excess radiation and signalling (for motility and gene expression). The chemical structure of the primary light-absorbing components in biology (the chromophores of photoactive proteins) is surprisingly simple: tetrapyrroles, polyenes and derivatised aromats are the most abundant ones. The same is true for the photochemistry that is catalysed by these chromophores: this is limited to light-induced exciton- or electron-transfer and photoisomerization. The apoproteins surrounding the chromophores provide them with the required specificity to function in various aspects of photosynthesis, photorepair, photoprotection and photosignalling. Particularly in photosynthesis several of these processes have been resolved in great detail, for others at best only a physiological description can be given. In this contribution we discuss selected examples from various parts of the field of photobiology of Bacteria. Most examples have been taken from the purple bacteria and the cyanobacteria, with special emphasis on recently characterised signalling photoreceptors inEctothiorhodospira halophila and inFremyella diplosiphon.

Notes: Abstract An experimental system based on a continuous flow reactor is presented, in which undisturbed sediment cores can be investigated with regard to the release of phosphorus to the overlying water and the characteristics of the interstitial water. In this system the effect of simulated vertical groundwater movement was also studied. The results of three preliminary experiments are shown: 1) undisturbed core, 2) downward migration, 3) upward migration. The latter two experiments showed a rapid loss of phosphorus from the system in contrast to the first experiment. This process was reflected in the phosphorus concentration of the interstitial water.

Notes: Abstract An experimental system based on a continuous flow reactor is presented, in which undisturbed sediment cores can be investigated with regard to the release of phosphorus to the overlying water and the characteristics of the interstitial water. In this system the effect of simulated vertical groundwater movement was also studied. The results of three preliminary experiments are shown: 1) undisturbed core, 2) downward migration, 3) upward migration. The latter two experiments showed a rapid loss of phosphorus from the system in contrast to the first experiment. This process was reflected in the phosphorus concentration of the interstitial water.

Notes: Abstract An experimental system based on a continuous flow reactor is presented, in which undisturbed sediment cores can be investigated with regard to the release of phosphorus to the overlying water and the characteristics of the interstitial water. In this system the effect of simulated vertical groundwater movement was also studied. The results of three preliminary experiments are shown: 1) undisturbed core, 2) downward migration, 3) upward migration. The latter two experiments showed a rapid loss of phosphorus from the system in contrast to the first experiment. This process was reflected in the phosphorus concentration of the interstitial water.

Notes: Abstract In order to assess possible phosphate limitation for the phytoplankton community of Lake Maarsseveen, two techniques (phosphate uptake experiments and bioassays) were employed simultaneously in February–March 1982. In that period the ambient phosphate concentration of the lake water was less than 0.03 µM P and the diatom Asterionella formosa constituted more than 90% of the phytoplankton population. The phosphate uptake experiments showed relatively high uptake capacities and low cell phosphorus contents for the natural phytoplankton community. This suggested phosphate limitation throughout the test period. The growth stimulation of the phytoplankton after enrichment with phosphate, however, only revealed phosphate limitation from the beginning of March and bioassays may therefore be regarded as a less sensitive method.

Notes: Summary The pigment composition of an alga determines which part of the solar spectrum can be used for photosynthesis. Chlorophyll absorbs red and blue light, phycocyanin (C-PC) absorbs orange light, while phycoerythrin (C-PE) absorbs green light. The phycobiliproteins (C-PC and C-PE) are possessed by red and brown algae and by cyanobacteria. The ability to adapt the pigment composition to the light quality is called chromatic adaptation;e.g. in green light C-PE is formed and in orange light C-PC is the main phycobiliprotein (TANDEAU DE MARSAC, 1977). In the deeper layers of a lake the light-climate will be green-because of the absorption in the epilimnion of red and blue light by the chlorophyll of the phytoplanktonso that C-PE-containing species are to be expected and are indeed found (FAAFENG and NILSSON, 1981; KONOPKA, 1980). The influence of the light quality on the growth of the green algaScenedesmus protuberans and two cyanobacteria, the ‘green’ (only C-PC containing)Oscillatoria agardhii and the ‘red’ strainO.agardhii var. 7821 (which possess both C-PC and C-PE) was investigated in dense, light-limited continuous cultures. The energy balance of algae, when limited in the light supply, can be described according to GONS and MUR (1975): $$\mu = c.q_E - \mu _e $$ where μ is the growth-rate (h−1), μe is the specific maintenance rate energy constant (h−) and qE is the specific light uptake rate (h−1); c is a growth efficiency factor which determines the efficiency of the transformation from absorbed light to biomass. It was found for the two cyanobacteria, when grown in green light, that there were no significant differences in the efficiency factor c. Furthermore it was found that c was influenced by the incident irradiance; c decreased when the incident irradiance increased. For the greenOscillatoria it appeared that the decrease in green light was greater than in white light. The maximum efficiency found was 0,22–0,25. This is close to the theoretical maximum of 0,25–0,28 (GONS, 1977). In red light, when there is a poor absorption of C-PC, the decrease in the c-value did hardly occur. The results suggest that the decrease of the efficiency factor c under green and white light was caused by a decrease of the efficiency of the transport of absorbed light from C-PC and C-PE to the chlorophyll-a of the reaction centres since no decrease in c occurred when chlorophyll was the main active pigment (i.e. in red light). The efficiency factor c ofS.protuberans was also investigated. c remained constant when the incident irradiance increased. In green light c was lower (0,1) than in white light (0,15). This was probably due to the relative great absorbance of nonphotosynthetic active components of the cell in green light. Growth kinetics, determined in dilute turbidostats, showed that in green lightO.agardhii var. 7821 grew faster than the green strain when the average irradiance was lower than 6 W.m−2, while in white light the green strain always grew faster than the red strain.Scenedesmus had. a greater growth-rate in white light thanO.agardhii at high irradiances. These results confirm the hypothesis that the redO.agardhii var. 7821 will inhabit the lower zones of the epilimnion or the metalimnion in stratified lakes (it possess a good buoyancy regulation) where exists a green lightclimate of low intensity, while the greenO.agardhii andS.protuberans are found in more shallow waters.