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When grown under a variety of stress conditions, cyanobacteria express the isiA gene, which encodes the IsiA pigment-protein complex. Overexpression of the isiA gene under iron-depletion stress conditions leads to the formation of large IsiA aggregates, which display remarkably short fluorescence lifetimes and thus a strong capacity to dissipate energy. In this work we investigate the underlying molecular mechanism responsible for chlorophyll fluorescence quenching. Femtosecond transient absorption spectroscopy allowed us to follow the process of energy dissipation in real time. The light energy harvested by chlorophyll pigments migrated within the system and eventually reaches a quenching site where the energy is transferred to a carotenoid-excited state, which dissipates it by decaying to the ground state. We compare these findings with those obtained for the main light-harvesting complex in green plants (light-harvesting complex II) and artificial light-harvesting antennas, and conclude that all of these systems show the same mechanism of energy dissipation, i.e., one or more carotenoids act as energy dissipators by accepting energy via low-lying singlet-excited S1 states and dissipating it as heat.  相似文献   
3.

As the anthropological theory of politeness has put it, people have universally two kinds of social want. They wish to be close to others, liked and accepted, but they also want some distance, freedom from imposition and respect of mutual difference. These wants, which one may also call basic human rights, are however often violated, and images play an important role in this.

Images are ultimately generated in the human mind and may find verbal as well as written and pictorial representation. Tyler [1978] has proposed a typology of mental images based on criteria of conscious control, completeness, abstraction, media and autonomy. These criteria also prove useful when probing into prototypical usages of intrusive imagery such as cursing, blessing, magic, witchcraft and the evil eye. Also the criteria help one understand the subtle process by which imagery can lead to the articulation and even discovery of peoples’ selves.

Ethnographic discourse has always been to a large extent about images, but until recently the ethnographer stood between his or her audience and the people of whom he or she was speaking or writing. Now, as sound recordings, film and video have arrived, this allows for richer varieties of cooperation where the non‐literate counterparts of the ethnographer can make more expressive and coherent contributions than before.

Also it seems that in the face of suppression people welcome the new media as a support in their ongoing battle for a recognition of their cultural and social worthiness.  相似文献   
4.
An HTY medium osmotically stabilized with 0.5 M D-glucitol was used for regeneration ofBacillus subtilis protoplasts. The application of glucitol as osmotic stabilizer allows simultaneous selection of cells resistant to kanamycin to be made since this antibiotic is not inactivated by glucitol when added to the regeneration medium.  相似文献   
5.
The course of biosynthesis of fatty acids in the seeds of winter rape (Brassica napus L. ssp.oleifera, f.biennis cv. T?ebí?ská) was investigated. After the termination of flowering seed samples were taken at five intervals, the seeds were divided into 4 fractions according to size, and their weight, water content, oil content and fatty acid composition were determined. The oil content was found to increase in all size categories with time, with the exception of a minute drop when complete maturity is reached. Larger seeds contained more oil. The fatty acid composition changes with time in the individual size fractions almost continuously. The same holds for differences between seed sizes of the same sample. The main change in oil composition consists in the decrease of C18 acids in favour of C22 acids. Greatest decrements during maturation were found with oleic acid, less with linoleic acid. In absolute amounts the quantity of all synthesized acids rises, the greatest rise being observed with C22 acids (i.e. predominantly erucic acid). It follows from the mean rates of synthesis of the individual groups (C16, C18, C20, C22) of fatty acids that the fraction of C22 rate of synthesis increases, while that of the C18 acids decreases with the same speed. The results indicate that the fatty acid synthesis is most intense during the second half of seed maturation, the main role being played by accelerating the synthesis of higher acids, especially of erucic acid.  相似文献   
6.
In our present work the formation of chromosome aberrations has been studied in dependence on the tima interval between sonication and fixation of the primary root tips of Vicia faba. Maximum occurrence of aberrations was recorded immediately after sonication. The results of our experiments pointed to the fact that the frequency of the induced changes was independent on the sonic waves intensity within the range of 0-2—3-0 W/cm2 and on ultrasond treatment duration within the range of 1—20 min. Studies of the distribution of chromosome abnormalities caused by ultrasound between the large and small chromosomes of theVicia faba meristematic cells in various time intervals showed that the frequency of the aberrations in both chromosome groups was proportional to its total metaphase lengths. Analysis of the type of aberrations observed in various time intervals after sonication indicated the simultaneous formation of chromosome and chromatide abnormalities.  相似文献   
7.
Algorithms predicting RNA secondary structures based on different folding criteria – minimum free energies (mfe), kinetic folding (kin), maximum matching (mm) – and different parameter sets are studied systematically. Two base pairing alphabets were used: the binary GC and the natural four-letter AUGC alphabet. Computed structures and free energies depend strongly on both the algorithm and the parameter set. Statistical properties, such as mean number of base pairs, mean numbers of stacks, mean loop sizes, etc., are much less sensitive to the choice of parameter set and even of algorithm. Some features of RNA secondary structures, such as structure correlation functions, shape space covering and neutral networks, seem to depend only on the base pairing logic (GC or AUGC alphabet). Received: 16 May 1996 / Accepted: 10 July 1996  相似文献   
8.
Gulls, as largely flexible opportunistic individuals, have been increasingly breeding in many cities around the world, but it is still unclear whether urban habitats are of equal or higher quality than traditional natural habitats or represent an ecological trap with immediate reproductive benefits but longer-term detrimental consequences to health. Here we present a study of breeding parameters (nest density, egg dimensions, clutch size, hatching success and adult body condition) and physiological parameters (erythrocyte sedimentation rate, heterophil/lymphocyte ratio, haemoglobin concentration and measurements of oxidative stress) as indicators of the general health condition of Yellow-legged Gull Larus michahellis adults and chicks from natural and urban colonies. Yellow-legged Gulls in the largest urban area (Porto) laid smaller eggs and clutches, showed a significantly lower occurrence of inflammatory processes in chicks, and showed a slower early chick growth than in the natural colony of Deserta. This suggests that urban gulls might be facing important trade-offs between the advantages of breeding in lower density urban colonies, with fewer intraspecific interactions and a lower disease transmission probability, and the disadvantages of having an anthropogenic diet usually lower in nutritional value.  相似文献   
9.
Summary The antitumor and antimetastatic activities of the water-soluble peptidoglycan monomer GlnNAc-Mur-NAc-L-Ala-D-iso-Gln-meso-diamminopimelic acid (-NH2)-D-Ala-D-Ala (PGM), which has immunostimulant effects, have been evaluated in CBA mice bearing MCa mammary carcinoma. The antineoplastic effects of PGM depend strictly on the dosage and treatment schedule used. Though a significant inhibition of the primary tumor growth is observed over a wide range of dosage, only the IV administration of daily doses of 50 mg/kg/day on days 1, 5, 10, 15 inhibits spontaneous lung metastasis formation and in parallel prolongs the survival time of the treated mice. The magnitude of the antimetastatic effects of PGM depends on the degree of dissemination of the tumor, and is greater when the number of metastatic foci is low. Examination of the therapeutic potential of PGM in combination with surgery has further indicated that the timing of administration plays an important role in the overall effectiveness of this substance. A 5-day interval is necessary between two consecutive injections for the induction of significant increases of the survival times.  相似文献   
10.
NaN3 was found to inhibit transformation but not the irreversible binding of donor3H-DNA in competent cells of the original low-transformable strainBacillus subtilis 168trp 2 . Addition of NaN3 to cells of two mutantsBacillus subtilis HT39 and HT46 with an increased transformability decreased substantially the irreversible binding of the donor DNA to the competent cells. The decreased irreversible binding of DNA is caused by an increased osmotic sensitivity of competent cells of the mutants HT39 and HT46 in the presence of NaN3, leading preferentially to lysis of the competent cells.  相似文献   
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