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61.
Toshimitsu Okeda Yasushi Yokogawa Hiroaki Ueo Mary A. Bury Paul O. P. Ts'o Sarah A. Bruce 《In vitro cellular & developmental biology. Plant》1990,26(12):1157-1166
Summary Primary cultures of 9-d-gestation Syrian hamster embryo (E9) cells are distinct from primary cultures of later gestational
age in terms of their growth and differentiation. First, primary E9 cell cultures express multiple mesenchymal differentiation
lineages (e.g., adipocyte, myoblast) only rarely seen in cultures of 13-d-gestation fetal (F13) cells. Second, although most
primary E9 cultures have a limited in vitro proliferative life span and exhibit cellular senescence similar to primary cultures
of F13 cells, E9 cultures seem to have higher frequency of escape from senescence and conversion to continuous cell lines
compared to F13 cells. Moreover, this frequency can be further increased 4- to 5-fold by continuous exposure of the E9 cells
to tumor promoters or epidermal growth factor. Eleven continuous cell lines have been isolated from unreated, promoter-treated,
or epidermal growth factor-treated primary E9 cultures. Seven of these are neoplastic or preneoplastic. However, the remaining
four do not show any evidence of being in neoplastic progression and three of these continue to express the same differentiated
phenotype observed in ther parental primary cell cultures.
These studies were supported in part by grants from the National Institutes of Health (AG 01998), Bethesda, MD, and the U.S.
Department of Energy (DE-A-C02-76-EVO-3280), Washington, DC. 相似文献
62.
63.
C. P. Chamberlain J. D. Blum R. T. Holmes Xiahong Feng T. W. Sherry G. R. Graves 《Oecologia》1996,109(1):132-141
To determine whether stable isotopes can be used for identifying the geographic origins of migratory bird populations, we
examined the isotopic composition of hydrogen (deuterium, δD), carbon (δ13C), and strontium (δ87Sr) in tissues of a migratory passerine, the black-throated blue warbler (Dendroica caerulescens), throughout its breeding range in eastern North America. δD and δ13C values in feathers, which are grown in the breeding area, varied systematically along a latitudinal gradient, being highest
in samples from the southern end of the species’ breeding range in Georgia and lowest in southern Canada. In addition, δD
decreased from east to west across the northern part of the breeding range, from New Brunswick to Michigan. δ87Sr ratios were highest in the Appalachian Mountains, and decreased towards the west. These patterns are consistent with geographical
variation in the isotopic composition of the natural environment, i.e., with that of precipitation, plants, and soils for
δD, δ13C, and δ87Sr, respectively. Preliminary analyses of the δD and δ13C composition of feathers collected from warblers in their Caribbean winter grounds indicate that these individuals were mostly
from northern breeding populations. Furthermore, variances in isotope ratios in samples from local areas in winter tended
to be larger than those in summer, suggesting that individuals from different breeding localities may mix in winter habitats.
These isotope markers, therefore, have the potential for locating the breeding origins of migratory species on their winter
areas, for quantifying the degree of mixing of breeding populations on migratory and wintering sites, and for documenting
other aspects of the population structure migratory animals – information needed for studies of year-round ecology of these
species as well as for their conservation. Combining information from several stable isotopes will help to increase the resolution
for determining the geographic origins of individuals in such highly vagile populations.
Received: 24 April 1995 / Accepted: 2 June 1996 相似文献
64.
J. Laybourn-Parry Mark R. James Diane M. McKnight John Priscu Sarah A. Spaulding Russell Shiel 《Polar Biology》1996,17(1):54-61
Samples collected from Lake Fryxell, southern Victoria Land, Antarctica in January 1992 and 1994 were analysed for the abundance
of bacterioplankton and the diversity and abundance of protistan plankton. At the times of sampling, 14 ciliate species and
10 species of autotrophic flagellate were recorded. The samples contained two species of rotifer (Philodina spp.), which formed the first record of planktonic metazoans in the Dry Valley lakes of this region of Antarctica. Bacterial
concentrations ranged between 1.0 and 3.8×108 l-1 in the upper oxic waters increasing to 20×108 l-1 in the anoxic waters. Heterotrophic flagellates decreased in abundance down the oxygenated water column, disappearing completely
at 9 m, and ranged between 0.28 and 7.39×105 l-1 in abundance. Autotrophic flagellates were much more abundant exhibiting a number of distinct peaks down the water column
(1.89–25.3×108 l-1). The ciliated protozoa were very abundant (up to 7720 l-1) in relation to flagellate and bacterial numbers, typical of oligotrophic lakes world-wide. The distribution of the protistan
plankton showed marked zonation, probably in response to the differing salinity and temperature gradients in the water column.
Possible trophic interactions are discussed and comparisons with other continental Antarctic lakes made.
Received: 29 November 1995/Accepted: 18 February 1996 相似文献
65.
Harold Gouzoules Sarah Gouzoules Kimran Miller 《International journal of primatology》1996,17(4):549-568
Signalers that misinform sufficiently open may become devalued as sources of information; however, “skepticism” and any comparison
involved in testing reliability entail a cost that involves delays and energy expenditure. Skepticism may be less costly though,
if, as a rule, animals are not equally skeptical of the signals of all conspecifics. Animals with the ability to recognize
individual conspecifics and to recall past encounters with them may have the capacity to restrict skepticism to subsets of
animals that are most likely to benefit from deception. We played tape-recorded alarm calls of high- and low-ranking rhesus
monkeys(Macaca mulatta) to their groups in a feeding context once daily over 8 consecutive days at the Yerkes Primate Center Field Station. Over
the sequence of playbacks, response was greater to the calls of high-ranking monkeys, adult response patterns were different
from those of juveniles, and for adults especially, decline in responsiveness was punctuated by partial resurgences of response.
These differences may be the consequence of the adults’ more extensive histories of interaction with group members that, though
generally reliable, vary with respect to the potential benefits of deceptive signaling. 相似文献
66.
67.
68.
Susan M. Rankin Sarah K. Storm Dana L. Pieto Andrea L. Risser 《Journal of Insect Behavior》1996,9(1):85-103
The expression and maintenance of maternal behavior in the earwig,Euborellia annulipes, was examined through manipulation of clutch size, age, and species and through observations of interactions between brooding females. Females underwent discrete gonadotrophic cycles culminating in oviposition of first clutches that were highly variable in size. Neither the head capsule width nor the age of the mother was correlated with clutch size. Maternal care extended through embryogenesis and for the week following hatching. Clutch removal significantly shortened the interclutch interval, indicating that the presence of brood inhibited the onset of the second gonadotrophic cycle. Brooding females readily accepted replacement clutches of the same age. Thus, mothers did not appear to distinguish their own eggs from those of other females. Experimental doubling of clutch size did not significantly reduce the proportion hatching or fledging. In contrast, reducing clutch size diminished the percentage successfully fledging. Manipulation of clutch age resulted in reduced hatching/fledging success. Placing two females, each with newly laid clutches, in the same cage usually resulted in egg transfer from the nest of one female to that of the other within 12 h. Nests of females with larger forceps were significantly more likely to contain both clutches. When mothers with first clutches were paired with mothers with third clutches, eggs were more likely to be transferred to the nest of the older female.E. annulipes females with newly laid clutches appeared to accept as replacement clutches eggs of the earwigDoru taeniatum. Alien clutches were maintained for the typical duration of embryogenesis; however, noD. taeniatum hatchlings were observed. 相似文献
69.
David McElroy Douglas A. Chamberlain Eunpyo Moon Kate J. Wilson 《Molecular breeding : new strategies in plant improvement》1995,1(1):27-37
The use of reporter genes to characterise sequence elements that act to regulate gene expression in transgenic plants has been vital to the development of foreign gene expression strategies for use in cereal transformation. ThegusA locus ofEscherichia coli, which encodes the enzyme-glucuronidase (GUS), is by far the most popular reporter gene used in plant transformation. In this paper we extend the utility of the GUS reporter gene system in cereal transformation by describing and evaluating a number of novel constructs suitable for use in direct gene transfer experiments. These plasmids are all available from the Molecular Genetic Resource Service of the Center for the Application of Molecular Biology to International Agriculture. 相似文献
70.
Abstract. The Argentine Chaco is a mosaic of grassland and open forest habitats maintained by natural disturbance activities such as fire. Since the introduction of domestic livestock and other human activities, the balance of this mosaic has been significantly altered, both in plant species and structural composition. This study focuses on the impact of such changes on the diversity of ground-dwelling arthropods within semi-arid Chaco forest. Quantitative measures of habitat structure and arthropod diversity were taken in forest areas previously subjected to grazing, logging and ploughing. Results indicated that arthropod diversity was smaller on sites with reduced structural complexity, with marked changes in arthropod family composition. The habitat components relating to plant architectural and vertical diversity were particularly influential on arthropod diversity. The guild size ratio of predatory to non-predatory arthropods also differed significantly between habitats suggesting a change in the resource base available to some groups. The latter suggests a shift in the functional organisation of the forest ecosystem which could have important repercussions for the diversity of other trophic levels. 相似文献