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21.
Slow (> 1 s) light-induced absorbance changes in the 475–530 nm spectral region were examined in Type A chloroplasts from spinach. The most prominent absorption change occurred at 505 nm. The difference spectrum for this light-induced increase, its absence in osmotically shocked chloroplasts and restoration by ascorbate, and its sensitivity to dithiothreitol indicate that the absorption change is due to carotenoid de-epoxidation. The reaction in intact chloroplasts is characterized by its independence of exogenous ascorbate and a rate constant 3- to 8-fold higher than that reported previously for chloroplasts supplemented with ascorbate.The relevance of carotenoid de-epoxidation to other photosynthetic processes was examined by comparing their sensitivities to dithiothreitol. Levels of dithiothreitol that eliminate the 505 nm shift are without effect on saturated rates of CO2 fixation and do not appreciably inhibit fluorescence quenching. We conclude that carotenoid de-epoxidation is not directly involved in the reactions of photosynthesis or in the regulation of excitation allocation between the photosystems. 相似文献
22.
The impact of ticks on pheasant territoriality 总被引:1,自引:0,他引:1
Pheasants are competent reservoir hosts for the Lyme disease spirochaete, Borrelia burgdorferi s.l., and carry large, but highly over-dispersed, infestations of the vector ticks, Ixodes ricinus . The effects of experimental reduction of tick infestation levels on the survival and territorial behaviour of male pheasants were studied. Over three years in two woodlands in southern England, birds were marked individually and half were fitted with a slow-release acaricide, which substantially reduced their tick burdens from March to August. Acaricide treatment affected reproductive success but had no discernible impact on the survival rates of male pheasants. The degree of wattle inflation by males, an indicator of territorial status and a correlate of harem acquisition, was significantly greater among treated males. In each year, a significantly higher proportion of treated (overall 44%) than control (22%) males acquired harems. Males that acquired females ranged over small areas on field edges. By contrast, those with no females ranged more widely in woods and the adjoining fields, increasing their exposure to questing ticks. The relative contribution of such roving males to tick-borne pathogen transmission may thus increase. 相似文献
23.
Patricia Pacheco Daniel J. Crawford Tod F. Stuessy Mario Silva O. 《American journal of botany》1991,78(4):534-543
Leaf flavonoid chemistry was examined from the three subgenera and 11 species of the endemic genus Dendroseris (Compositae, Lactuceae) of the Juan Fernandez Islands, Chile. Eight of the species are restricted to the older island (Masatierra, ca. 4 million years old), which is also closer to the mainland. Three species, one from each subgenus, are restricted to Masafuera, which is younger geologically (1–2 million years old) and 145 km further west of Masatierra. A total of 16 compounds was identified, with the 7-0-glucosides of the flavones apigenin and luteolin accounting for 12 of the constituents. Two glucosides of the flavonol quercetin were detected. Despite considerable interpopulation variation within species, six of the taxa have distinctive flavonoid profiles. Although there are few absolute differences among the subgenera, they can be distinguished chemically. Subgenus Rea contains the greatest number of compounds, and a previous cladistic analysis based on morphological features suggested this subgenus as most primitive. Subgenus Phoenicoseris is considered highly derived morphologically, and it has a reduced flavonoid chemistry. Very little reduction in flavonoid diversity was seen in the morphologically specialized subg. Dendroseris as compared to subg. Rea. A trend in reduction of numbers of compounds was seen for two of the three species on the younger island of Masafuera when compared to their presumed ancestors on Masatierra. Flavonoids of selected species of Hieracium and Hypochaeris, presumptive mainland progenitors of Dendroseris, reveal a close chemical affinity with the former genus. 相似文献
24.
Patricia M. Lambert 《American anthropologist》2000,102(1):166-167
Prehistoric Warfare in the American Southwest. Steven A. LeBlanc. Salt Lake City: University of Utah Press, 1999 400 pp. 相似文献
25.
Michael B. Bonsall Michael P. Hassell Patricia M. Reader T. Hefin Jones 《Ecological Entomology》2004,29(6):639-647
Abstract. 1. This study explored the temporal and spatial aspects of coexistence over many generations in a multispecies host–parasitoid assemblage.
2. The long-term interaction between the cabbage root fly, Delia radicum (Diptera: Anthomyiidae), and two of its natural enemies, Trybliographa rapae (Hymenoptera: Fitigidae) and Aleochara bilineata (Coleoptera: Staphylinidae), in a cultivated field at Silwood Park over 19 years was explored.
3. Although time series showed that the populations were regulated, the impact of the natural enemies was highly variable. Within-year determinants showed that the spatial response of the specialist parasitoid, T. rapae , was predominantly independent of host density while A. bilineata acted simply as a randomly foraging generalist parasitoid.
4. These findings are compared and contrasted with an earlier investigation of the same system when only the first 9 years of the time series were available. This study demonstrated the potential of long-term field studies for exploring hypotheses on population regulation, persistence, and coexistence. 相似文献
2. The long-term interaction between the cabbage root fly, Delia radicum (Diptera: Anthomyiidae), and two of its natural enemies, Trybliographa rapae (Hymenoptera: Fitigidae) and Aleochara bilineata (Coleoptera: Staphylinidae), in a cultivated field at Silwood Park over 19 years was explored.
3. Although time series showed that the populations were regulated, the impact of the natural enemies was highly variable. Within-year determinants showed that the spatial response of the specialist parasitoid, T. rapae , was predominantly independent of host density while A. bilineata acted simply as a randomly foraging generalist parasitoid.
4. These findings are compared and contrasted with an earlier investigation of the same system when only the first 9 years of the time series were available. This study demonstrated the potential of long-term field studies for exploring hypotheses on population regulation, persistence, and coexistence. 相似文献
26.
Geoffrey W. Krissansen Patricia A. Gorman Christine A. Kozak Nigel K. Spurr Denise Sheer Peter N. Goodfellow Michael J. Crumpton 《Immunogenetics》1987,26(4-5):258-266
The gene coding for the M
r 26000 chain of the human CD3 (T3) antigen/T-cell antigen receptor complex was mapped to chromosome band 11q23 by using a cDNA clone (pJ6T3 -2), by in situ hybridization to metaphase chromosomes and by Southern blot analysis of a panel of human-rodent somatic cell hybrids. The mouse homolog, here termed Cdg-3, was mapped to chromosome 9 using the mouse cDNA clone pB10.AT3 -1 and a panel of mouse-hamster somatic cell hybrids. Similar locations for the CD3
genes have been described previously. Thus, the corporate results indicate that the CD3
and genes have remained together since they duplicated about 200 million years ago. 相似文献
27.
The activities of -2-l-fucosyltransferase and -3-l-fucosyltransferase were measured in human platelets and leucocytes from normal donors, -2-l-Fucosyltransferase was found in platelets but not in leucocytes. In contrast -3-l-fucosyltransferase was not detected in platelets but was present in leucocytes where it was demonstrated in the neutrophil, monocyte and lymphocyte fractions. 相似文献
28.
Marion H. Brown Patricia A. Gorman William A. Sewell Nigel K. Spurr Denise Sheer Michael J. Crumpton 《Human genetics》1987,76(2):191-195
Summary A cDNA clone encoding the human T lymphocyte sheep erythrocyte receptor [the CD2 (T11) antigen] was used as a probe to define the chromosomal location of the gene. The signal, revealed by hybridisation to Southern blots of genomic DNA from somatic cell hybrids, showed a high degree of concordance for human chromosome 1. In particular, the hybrid F4Sc13C19 which contained the short arm only of human chromosome 1 was positive. The location of the CD2 gene to 1p13 was confirmed by in situ hybridisation. 相似文献
29.
Our goal was to test our understanding of ingestion, assimilationefficiency and metabolism for Mnemiopsis mccradyi by formulatingand validating a simulation model of growth under differentconditions of food availability. The model was based on a carbonbudget approach using formulations derived from empirical results,including how each process was affected by food availabilityand ctenophore size. An experimentally measured carbon budgetfor pulsed food availability indicated that, relative to totalingestion, growth was high (1748%), respiration plusorganic release was relatively low (2448%) and little(<10%) of the ingested carbon was unaccounted for. New laboratoryinvestigations of feeding and assimilation efficiency were necessaryto refine the formulations so that model predictions comparedfavorably with a variety of laboratory measurements of growth,and growth efficiency, as well as the complete experimentallymeasured carbon budget. The refined model predicted a high ratioof growth to metabolism (>2) and a high gross growth efficiency(>30%) for smaller ctenophores at high food concentrations(>20 prey l1). Both growth rates and growth efficiencieswere predicted to decrease for larger ctenophores. Model predictionswere generally consistent with experimental results, includinginvestigations using pulsed food availability to simulate environmentalpatchiness. Although the model underpredicted ctenophore growthin some experiments at low food densities, the model predictionof a minimum prey concentration of about 8 l1 (24 µgC l1) for sustaining a ctenophore population of reproductivesize agreed with field observations. 相似文献
30.
This paper contains new experimental data on the growth dynamicsof a lobate coastal ctenophore, Mnenmiopsis mccradyi, whichadd significantly to our understanding of the nutritional ecologyof ctenophores and their role as opportunistic predators. Theseexperimental observations were necessary to refine the dynamiccarbon budget presented as a simulation model in another report.The ratio of carbon biomass to dry weight may vary several-folddepending on the nutritional state and size from >12% inwell-fed larvae to <1% in starved adults. Feeding effort(clearance rate) is higher for previously starved animals, fallingsharply within a few hours after re-exposure to food. Directvisual observations of feeding activity of animals confirmedthis. Assimilation efficiency can be high (72%) in these animalsbut if they continue to feed at high food concentrations, incomingfood displaces material which is only partially digested andassimilation efficiency decreases substantially. Except at verylow food concentrations, growth efficiency ranges between 20and 45%. Mnemiopsis, begins to produce eggs at a size much lessthan its maximum. Egg production is very sensitive to food supply,and somatic growth is favored over egg production at low fooddensities. Even though several thousand eggs may be producedover a few days, they represent <2% day1 of the carbonbiomass of the ctenophore and several-fold less than respiratorycarbon. 相似文献