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2.
Schubert Hendrik; Schiewer Ulrich; Tschirner Erhard 《Journal of plankton research》1989,11(2):353-359
The fluorescence characteristics of the cyanobacteria Synechocystisaquatilis Sauv., Microcystis firma (Breb. et Lenorm.) Schmidleand Synechococcus leopoliensis (Racib.) Kom. and the green algaScenedesmus quadricauda (Turp.) Breb. were examined. In thethree cyanobacteria, phycocyanin is the main accessory pigment.Phycoerythrin is not present in our investigated strains ofcyanobacteria. The highest excitation of the chlorophyll a (Chla) fluorescence of cyanobacteria resulted from light with wavelengthsof 620630 nm. A definite Kautsky effectis also evident at this wavelength. However, excitation withblue light (420520 nm) produced only very slight fluorescence.The Kautsky effect is not evident at these wavelengths, evenat high photon flux densities. For Scenedesmus, fluorescencecharacteristics typical of green algae were found. The fluorescenceexcitation of cyanobacteria at 620 nm corresponds to a photosynthesispeak in the action spectrum measured in terms of O2 production.The results underline the necessity of fluorescence measurementsat several wavelengths whenever mixed populations are involved.Such measurements also present possibilities for more accurateestimation of biomass and potential photosynthetic productionin mixed populations. 相似文献
3.
Rolf Erhard 《Development genes and evolution》1959,151(4):381-429
Ohne ZusammenfassungDie Arbeit wurde auf Anregung von Herrn Prof. Dr. H.Wurmbach ausgeführt. Ich danke ihm für die freundliche Förderung der Arbeit, sowie Herrn Prof. Dr. A.Goebel, Pathol. Inst. d. Univ. Köln, für wertvolle Hinweise. Die Untersuchungen wurden von derDeutschen Forschungsgemeinschaft, Bad Godesberg, gefördert. 相似文献
4.
Adaptation of Escherichia coli to high osmolarity environments: Osmoregulation of the high-affinity glycine betaine transport system ProU 总被引:10,自引:0,他引:10
Abstract: A sudden increase in the osmolarity of the environment is highly detrimental to the growth and survival of Fscherichia coli and Salmonella typhimurium since it triggers a rapid efflux of water from the cell, resulting in a decreased turgor. Changes in the external osmolarity must therefore be sensed by the microorganisms and this information must be converted into an adaptation process that aims at the restoration of turgor. The physiological reaction of the cell to the changing environmental condition is a highly coordinated process. Loss of turgor triggers a rapid influx of K+ ions into the cell via specific transporters and the concomitant synthesis of counterions, such as glutamate. The increased intracellular concentration of K+ -glutamate allows the adaptation of the cell to environments of moderately high osmolarities. At high osmolarity, K+ -glutamate is insufficient to ensure cell growth, and the bacteria therefore replace the accumulated K+ ions with compounds that are less d eleterious for the cell's physiology. These compatible solutes include polyoles such as trehalose, amino acids such as proline, and methyl-amines such as glycine betaine. One of the most important compatible solutes for bacteria is glycine betaine. This potent osmoprotectant is widespread in nature, and its intracellular accumulation is achieved through uptake from the environment or synthesis from its precursor choline. In this overview, we discuss the properties of the high-affinity glycine betaine transport system ProU and the osmotic regulation of its structural genes. 相似文献
5.
Hilary Woodcock Pierre Vollenweider Rolf Dubs Rose-Marie Hofer 《Trees - Structure and Function》1995,9(5):279-288
One of the first symptoms expressed by declining trees is reduced growth in stem diameter and length increment. The possibility of a relationship between length increment and crown thinning in beech (Fagus sylvatica L.) was investigated by developing a computer model to simulate first order branching patterns of the apical 2 m of monopodially branching beech trees, 70–100 years old, for a range of length increment rates. The model was based on values for branching angle, main axis and branch length increment, number of branches produced per year and branch mortality rates for six healthy and declining trees. Shoot growth rates in the apical 2 m of the sample trees ranged from about 5 cm/year (decline class 3) to 43 cm/ year (healthy). Simulations of branching patterns in the apical 2 m of trees growing at different rates indicated that, when growth rate exceeded about 20 cm/year, total first order branch length and area explored were independent of growth rate. When growth rates fell below this value there was a reduction in total area explored and first order branch length due primarily to the formation of fewer branches. More acute branching angles contributed to a reduction in the area explored. Growth rate-related crown thinning could increase the risk of bark necrosis and secondary pathogen infection during dry and/or hot spells. 相似文献
6.
H O Hofer 《Gegenbaurs morphologisches Jahrbuch》1977,123(6):836-856
Nycticebus coucang is typically strepsirrhine. This condition is basically the same in all prosimians except Tarsius. The rhinarium shows a labial part; the marked furrow in its median plane clefts the margin of the upper lip. The latter is attached to the gum between the median incisors by means of paired folds (not corresponding to a frenulum labii superioris). The labial cleft is continued in the sulcus papillae palatinae. The ductus vomeronasalis opens into the ductus nasoplatinus which, in turn, enters the aboral part of the sulcus palatinus. Thus strepsirrhinism provides, occasionally, an open communication of the olfactory systems (nose, vomeronasal organ) with the environment in front of the rhinarium. Strepsirrhine primates possess an internarium very similar to the one of platyrrhine monkeys. The shape of the nostrils is not characteristics for strepsirrhinism. A split-lip condition is likely ancestral to the complete lip condition, since it is found in several stems of mammals, especially in archaic forms. Strepsirrhinism, such as in lemuroid prosimians, is probably just one case of the primitive split-lip condition. Therefore, a median furrow in the external hairy skin of the upper lip, found in some platyrrhine monkeys, could be a rudiment of a cleft, indicating that a kind of a split lip condition was ancestral to the undivided lips of platyrrhine monkeys. Taste buds occur in the epithelium of the lateral surface of the papilla palatina of Nycticebus. Other lorisid prosimians have not been studied in this respect. The taste buds test water soluble substances entering the sulcus either way. These substances may come from the environment entering the sulcus through the labial cleft. 相似文献
7.
M Pospísil J Sandula I Pipalová M Hofer S Viklická 《Physiological research / Academia Scientiarum Bohemoslovaca》1991,40(4):377-380
Carboxymethylglucan, a novel soluble derivative of beta-1,3-glucan, was found to enhance hemopoietic recovery in sublethally gamma-irradiated mice and to increase survival in lethally irradiated animals when given 24 hours prior to irradiation. Postirradiation treatment with carboxymethylglucan also induced favourable effects in terms of survival when used in combination with preirradiation cystamine administration. 相似文献
8.
9.
Margret Bronder Hildegard Mell Erhard Stupperich Achim Kröger 《Archives of microbiology》1982,131(3):216-223
- With fumarate as the terminal electron acceptor and either H2 or formate as donor, Vibrio succinogenes could grow anaerobically in a mineral medium using fumarate as the sole carbon source. Both the growth rate and the cell yield were increased when glutamate was also present in the medium.
- Glutamate was incorporated only into the amino acids of the glutamate family (glutamate, glutamine, proline and arginine) of the protein. The residual cell constituents were synthesized from fumarate.
- Pyruvate and phosphoenolpyruvate, as the central intermediates of most of the cell constituents, were formed through the action of malic enzyme and phosphoenolpyruvate synthetase. Fructose-1,6-bisphosphate aldolase was present in the bacterium suggesting that this enzyme is involved in carbohydrate synthesis.
- In the absence of added glutamate the amino acids of the glutamate family were synthesized from fumarate via citrate. The enzymes involved in glutamate synthesis were present.
- During growth in the presence of glutamate, net reducing equivalents were needed for cell synthesis. Glutamate and not H2 or formate was used as the source of these reducing equivalents. For this purpose part of the glutamate was oxidized to yield succinate and CO2.
- The α-ketoglutarate dehydrogenase involved in this reaction was found to use ferredoxin as the electron acceptor. The ferredoxin of the bacterium was reoxidized by means of a NADP-ferredoxin oxidoreductase. Enzymes catalyzing the reduction of NAD, NADP or ferredoxin by H2 or formate were not detected in the bacterium.
10.
The crystal structure of the cyclic peptide disulfide has been determined by X-ray diffraction. The peptide crystallizes in the space group P212121, with a = 8.646(1), b = 18.462(2), c = 19.678(3)Å and Z = 4. The molecules adopt a highly folded compact conformation, stabilized by two intramolecular 4→ 1 hydrogen bonds between the Cys (1) and Pro (2) CO groups and the Cys (4) and methylamide NH groups, respectively. The backbone conformational angles for the peptide lie very close to those expected for a 310 helix. The S-S bridge adopts a right handed twist with a dihedral angle of 82°. The structure illustrates the role of stereochemically constrained residues, in generating novel peptide conformations. 相似文献