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1.
The Ultrastructure of Myosin-Extracted Striated Muscle Fibers 总被引:1,自引:0,他引:1
Electron microscope examination of myosin-extracted psoas muscleof the rabbit reveals a number of thin filaments, about 25 Äin diameter, bridging the gap between the ends of the actinsand the remaining myosin of the M band. Extraction of actinfrom the region of the Z disc shows similar thin filaments nearthe Z disc. Myosin-extraction of several invertebrate musclesreveals a remaining network of thin filaments in the regionof the A band. These thin filaments are probably elastic, andcould contribute to the functioning of these muscles. 相似文献
2.
BENJAMIN M. WAGGONER 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1994,27(1):77-84
The ‘osseous’ amber from the Cenomanian of northwestern France contains numerous microscopic inclusions, some of which are fairly well preserved and identifiable as protists. This paper describes three cyanobacteria similar to modern Plectonema. Lyngbya, and Coelosphaeriunr, fungus-like fossils of uncertain affinities (cf. ?Candida); a colorless chrysomonad similar to Monas; a desmid identical with Closterium; and naked ciliates of uncertain affinities (cf. Cyrtolophosis). All of these fossils are in a single sample of amber from Bretagnolles (Eure Département). This assemblage is comparable to modern limnetic microbial communities. It is typical of shallow freshwater environments in which productivity and respiration are both high. This interpretation fits paleoecological reconstructions drawn from the arthropod fossils from French amber. ***Chrysomonads, ciliates, Cretaceous, cyanobacteria, desmids, fungi, micropaleontology. 相似文献
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4.
Physiological responses to root pruning were investigated bycomparing 14CO2 fixation rates, the partitioning of 14C-labelledassimilate, and soluble and insoluble carbohydrate levels inthe leaves of carrot plants following the removal of some ofthe fibrous roots, or fibrous roots and part of the tap root.Root pruning reduced 14CO2 fixation by 2845% but leafspecific activity (14C assimilation g-1 leaf fresh weight) wasunchanged. The proportion of total assimilate exported to theroot system increased following root pruning and this was atthe expense of the developing leaves. In younger plants (wherethe tap root received 10% of the assimilate) the supply of 14Cto the tap root was maintained in spite of root pruning. However,shortening the tap root to 3 cm in older plants (in which 30%of the fixed 14C was normally exported to the developing storageorgan), reduced its sink capacity and resulted in slightly greaterretention of 14C in the mature leaves. Greater concentrationsof insoluble carbohydrate were found in the mature leaves followingroot pruning but soluble sugar content was unaffected. Onlysmall differences were observed in the distribution of 14C betweensoluble and insoluble carbohydrate fractions when plants werefed 14CO2 several days after the root pruning operations. Thesephysiological responses were mainly associated with the removalof fibrous roots and support the view that the fibrous rootsystem is more important than the developing storage organ inregulating growth in young carrot plants. 相似文献
5.
THE RATIO OF CALCAREOUS AND ORGANIC SHELL COMPONENTS OF FRESHWATER SPHAERIID CLAMS IN RELATION TO WATER HARDNESS AND TROPHIC CONDITIONS 总被引:1,自引:0,他引:1
BURKY ALBERT J.; BENJAMIN MICHELE A.; CATALANO DENNIS M.; HORNBACH DANIEL J. 《Journal of Molluscan Studies》1979,45(3):312-321
Shells from 14 populations of sphaeriid clams including Sphaeriumstriatinum, S. simile, Pisidium walkeri, Musculim partumeiumand M. iransversum were analyzed for organic carbon (µgCmg1 shell), nitrogen (µg,N mg1 shell) andCaCOs (%CaCO3 of total clam dry weight). Habitat waters wereassessed for total hardness (expressed as ppm CaCo3), ppm Ca,ppm Mg, conductivity (µmho) and suspended organic Carbon(µgCl1). For all populations, shell organic C andN are positively correlated and there is an inverse relationshipbetween the amounts of shell CaCO3 and shell organic carbon.Trophic considerations give the best correlation with shelltype at the generic level of consideration since species ofMusculium are found at the opposite end of the trophic scale(eutrophic) from all other populations studied. For S. striatinum,the most extensively studied species, the amount of shell CaCO3is inversely related to water hardness. The selection of shellsin the Sphaeriidae is discussed in relation to structural-functionalneeds and habitat conditions
1 Present Address: Department of Biology, Syracuse University,Syracuse, New York 13210, U.S.A.
2 Present Address: Department of Zoology, Miami University,Oxford, Ohio 45056, U.S.A. (Received 5 December 1978; 相似文献
6.
MARC J. FAZIO ALBA C. DA SILVA THOM K. ROSIERE G. BENJAMIN BOUCK 《The Journal of eukaryotic microbiology》1995,42(5):570-580
ABSTRACT. Proteins of the membrane skeleton of Euglena gracilis were extensively phosphorylated in vivo and in vitro after incubation with [32 P]-orthophosphate or γ-[32 P] ATP. Endogenous protein threonine/serine activity phosphorylated the major membrane skeletal proteins (articulins) and the putative integral membrane protein (IP39) anchor for articulins. The latter was also the major target for endogenous protein tyrosine kinase activity. A cytoplasmic domain of IP39 was specifically phosphorylated, and removal of this domain with papain eliminated the radiolabeled phosphoamino acids and eliminated or radically shifted the PI of the multiple isoforms of IP39. In gel kinase assays IP39 autophosphorylated and a 25 kDa protein which does not autophosphorylate was identified as a threonine/serine (casein) kinase. Plasma membranes from the membrane skeletal protein complex contained threonine/serine (casein) kinase activity, and cross-linking experiments suggested that IP39 was the likely source for this membrane activity. pH optima, cation requirements and heparin sensitivity of the detergent solubilized membrane activity were determined. Together these results suggest that protein kinases may be important modulators of protein assembly and function of the membrane skeleton of these protistan cells. 相似文献
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8.
Ovariole number in insects determines potential fecundity and can be influenced by genes, environmental conditions during development and parental effects. In the present study, three hypotheses are tested for ovariole number determination in the grasshopper Romalea microptera (Beauvois), which exhibits both intra‐ and interpopulation variation in ovariole number. In hypothesis 1, variation in ovariole number is a result of genetic variation. In hypothesis 2, ovariole number is influenced by nutrition during development. In hypothesis 3, ovariole number is influenced by maternal nutritional status. Females from four treatments are compared: low‐food, high‐food, daughters of low‐food, and daughters of high‐food. There is a relationship between parent and offspring ovariole number despite different environments, supporting hypothesis 1. Also, ovariole numbers are slightly, but significantly lower in individuals fed a low‐food diet compared with a high‐food diet, supporting hypothesis 2. Hypothesis 3 is not supported: starved and well‐fed females produce eggs of similar mass, as well as offspring with similar numbers of ovarioles, suggesting that the nutritional status of mothers does not influence offspring mass or offspring ovariole number. The results imply that genetic variation and developmental conditions determine ovariole number in this species but maternal environment does not. These results conflict with previous studies of ovariole determination in grasshoppers and locusts. 相似文献
9.
Effects of a Range of O2 Concentrations on Porosity of Barley Roots and on their Sugar and Protein Concentrations 总被引:1,自引:0,他引:1
Barley was grown at a range of oxygen concentrations (0.59mg l1), in nutrient solutions. Growth of both shootsand seminal roots was restricted by O2 concentrations lowerthan 23 mg l1) but nodal root growth was not. Root porosities were increased even at those O2 concentrationswhich did not restrict growth, and were inversely proportionalto the protein levels of the roots. Sugar concentrations increasedappreciably only at those O2 concentrations which also restrictedgrowth. Hordeum vulgare L., barley, root porosity, sugar, protein, oxygen concentration 相似文献
10.
GARY M. KOEHLER BENJAMIN T. MALETZKE JEFF A. VON KIENAST KEITH B. AUBRY ROBERT B. WIELGUS ROBERT H. NANEY 《The Journal of wildlife management》2008,72(7):1518-1524
Abstract Lynx (Lynx canadensis) occur in the northern counties of Washington state, USA; however, current distribution and status of lynx in Washington is poorly understood. During winters 2002–2004 we snow-tracked lynx for 155 km within a 211-km2 area in northern Washington, to develop a model of lynx-habitat relationships that we could use to assess their potential distribution and status in the state. We recorded movements and behaviors of lynx with a Global Positioning System and overlaid digitized lynx trails on various habitat layers using a Geographic Information System. Based on univariate analyses, lynx preferred Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa) forests, with moderate canopy and understory cover, and elevations ranging from 1,525 m to 1,829 m but avoided Douglas-fir (Pseudotsuga menziesii) and ponderosa pine (Pinus ponderosa) forests, openings, recent burns, open canopy and understory cover, and steep slopes. A map of suitable lynx habitat based on a logistic regression model built using these candidate variables revealed that habitats at elevations >1,400 m where lynx historically occurred in Washington are intersected and fragmented by landscape features and forest conditions that are generally avoided by lynx. Our habitat suitability map predicts 3,800 km2 of lynx habitat in Washington that could support 87 lynx, far fewer than previous estimates. Since 1985, natural fires have burned >1,000 km2 of forested habitat in Okanogan County, the only region in Washington where lynx occurrence has been documented during that period. Loss of suitable habitat from natural and human-caused disturbances, and the lack of verifiable evidence of lynx occurrence in historic lynx range, suggests that fragmented landscape conditions may have impeded recolonization of these areas by lynx. Consequently, translocations may be necessary to ensure lynx persistence in Washington. We suggest that managers assess the potential for translocation by first identifying the scale and distribution of potential foraging habitats for lynx based on our or similar habitat models, survey various habitat conditions to obtain reliable estimates of snowshoe hare densities, and identify a genetically compatible source population of lynx. If habitat and source populations are adequate, reintroducing lynx to areas of their historic range may be an appropriate conservation strategy. 相似文献