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21.
Christian Biémont Cristina Vieira Christine Hoogland Géraldine Cizeron Catherine Lœvenbruck Claude Arnault Jean-Pierre Carante 《Genetica》1997,100(1-3):161-166
To investigate the main forces controlling the containment of transposable elements (TE) in natural populations, we analyzed
the copia, mdg1, and 412 elements in various populations of Drosophila melanogaster and D. simulans. A lower proportion of
insertion sites on the X chromosome in comparison with the autosomes suggests that selection against the detrimental effects
of TE insertions is the major force containing TE copies in populations of Drosophila. This selection effect hypothesis is
strengthened by the absence of the negative correlation between recombination rate and TE copy number along the chromosomes,
which was expected under the alternative ectopic exchange model (selection against the deleterious rearrangements promoted
by recombination between TE insertions). A cline in 412 copy number in relation to latitude was observed among the natural
populations of D. simulans, with very high numbers existing in some local populations (around 60 copies in a sample from Canberra,
Australia). An apparent absence of selection effects in this Canberra sample and a value of transposition rate equal to 1–2
× 10-3 whatever the population and its copy number agree with the idea of recent but temporarily drastic TE movements in local populations.
The high values of transposition rate in D. simulans clearly disfavor the hypothesis that the low amount of transposable elements
in this species could result from a low transposition rate.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
22.
23.
24.
Summary When the Na electrochemical potential difference across the skin (Na) is altered by perturbing the transmembrane electrical potential difference or the external Na concentration, effects on transport and associated oxygen consumption can be described by the formalism of linear nonequilibrium thermodynamics (Vieira, Caplan & Essig, 1972,J. Gen. Physiol.
59:77; Danisi & Lacaz-Vieira, 1974,J. Gen. Physiol.
64:372; Procópio and Lacaz-Vieira, 1977,J. Membrane Biol.
35:219). We now show that with modifications of Na by substitution of Li or choline for Na in the inner bathing solution, this formalism is no longer applicable. Inner Na by K substitution ((Na×K)
i
) causes profound alterations in short-circuit current (SCC),J
Na
in
, K efflux (J
K
eff
) and PD. SCC drops transiently after (Na×K)
i
in Cl and in SO4 media, increasing subsequently. In Cl medium, following the initial transient, there is a late decline in SCC toward a steady state. The rate of SCC decline in Cl medium is more pronounced than that observed in SO4 medium. (Na×K)
i
causes a transient increase inJ
Na
in
with a peak synchronous to the minimum in SCC, both in Cl and in SO4 media. This was interpreted as due to depolarization of the inner membrane. In SO4 medium, following the peak observed after (Na×K)
i
J
Na
in
drops, to increase again toward a steady state in which SCC andJ
Na
in
are not statistically different, resembling the control condition before (Na×K)
i
. In Cl medium, however, theJ
Na
in
steady state is approximately 100% higher than SCC. This difference is due to an important K efflux (J
K
eff
), which builds up progressively after the substitution. The apparent K permeability [J
K
eff
/(K
i
)] is of comparable magnitude in Cl and in SO4 media before (Na×K)
i
, the apparent K permeability increases one order of magnitude as compared to the control condition before the ionic substitution. In Cl medium, the high levels ofJ
Na
in
and ofJ
K
eff
observed in the steady state after (Na×K)
i
were interpreted as being a consequence of cell swelling. SCC and PD follow very different temporal patterns after (Na×K)
i
which are characterized by transients in SCC and a simple fall in PD. Reasons for these differences are discussed. 相似文献
25.
H. Mercier C. C. J. Vieira R. C. L. Figueiredo-Ribeiro 《Plant Cell, Tissue and Organ Culture》1992,28(3):249-254
Leaf and stem segments of Gomphrena officinalis originated from aseptically grown seedlings were used to initiate cultures. Callus production was obtained on gelled Murashige & Skoog medium supplemented with 6-benzylaminopurine alone (1.0, 5.0 or 10.0 mgl-1) or combined with -naphthalene acetic acid (0.1, 0.5 and 1.0 mgl-1) after 10 to 15 days of culture, and can be transferred to fresh medium every 30 days. The combinations of 5.0 or 10.0 mgl-1 of 6-benzylaminopurine with 0.1 mgl-1 of -naphthalene acetic acid were found to be the best for shoot regeneration. Adventitious shoot formation occurred after 50 to 60 days of culture in leaf and internode stem explants. Nodal segments developed actively growing lateral buds after 30 days of culture. Gelled Murashige & Skoog medium containing 10 mgl-1 of indole-3-butyric acid was considered optimal for the rooting of shoots. Rooted plants transferred to potting soil could be successfully established.Abbreviations BA
6-benzylaminopurine
- IAA
indole-3-acetic acid
- IBA
indole-3-butyric acid
- MS
Murashige & Skoog
- NAA
-naphthalene acetic acid 相似文献
26.
Summary Cellulolytic fungi were isolated from rotting leaves and tested for extra-cellular cellulase activities (CMCase, avicelase, cellobiase and xylanase). The effect of the proportion of the enzyme activities on the rate of degradation of leached beet cosette was observed using a range of supernatant fluids in appropriate combinations. At low cosette concentrations (1.5–3.0 g/l), avicelase and cellobiase were the rate limiting enzymes; avicelase in the initial stages of reaction and cellobiase after 6–8 hours, when cellobiose inhibition becomes important. A ratio of celiobiase to avicelase of approx 2.0 was established as appropriate. At higher substrate concentrations (10 g/l, 40 g/l) the best cellobiase to avicelase ratio was maintained and up to 40% hydrolysis was obtained in the 10 g/l incubation with 10 Uav/l and 20 Ucellob/l. At 100 g/l cosette concentration, substrate inhibition was observed. 相似文献
27.
De Moraes DJ Abilio FM Cunha M Feitosa LA Aragão E Cysne E Vieira R Glavam HC Zaniolo W Netto MS Villela RD Labrunie P 《Cardiovascular diseases》1979,6(2):144-152
Thirteen patients were submitted to direct myocardial revascularization (saphenous vein graft) without the use of an artificial oxygenator. The perfusion was done by a left ventricle-to-aorta bypass and autogenous oxygenation. Most patients had three grafts implanted plus endarterectomy of the distal right coronary artery. There was one hospital death that was apparently not related to the method used. Perfusion time ranged from 45 minutes to 4 hours. Body temperature during perfusion was kept between 25 and 30 degrees C. Perfusion flow was maintained between 25 to 50 ml per kg of body weight per minute. Ischemic, hypothermic cardiac arrest was employed. We demonstrated for the first time that perfusion for this kind of heart surgery could be done with no artificial oxygenators and, apparently, is safer for the patients. There were no bleeding problems even in perfusions as long as 4 hours. There was no respiratory dysfunction, and artificial respiration was used for only 6 to 12 hours. The patients awoke at the end of surgery with no signs or symptoms of central nervous system damage, and vasopressor drugs were rarely used after surgery. Although the experience is very small, it suggests that many postoperative problems, especially those related to bleeding and respiratory dysfunction may be reduced or eliminated by this new method. 相似文献
28.
Ines Gerson Robert L. Seecof Raymond L. Teplitz 《In vitro cellular & developmental biology. Plant》1976,12(9):615-622
Summary Cultures of embryonicDrosophila melanogaster cells were examined by electron microscopy and events in myogenesis were recorded. Thick and thin myofilaments, T-tubules
and sarcoplasmic reticulum all appeared at about the same time, 10.5 hr. This was about 5 hr after the final division of myoblasts
and about the time that muscle cells were elongating, aligning and fusing. Sarcoplasm typical of insect muscle was detected
by 18.5 hr, as were myotendonal and tendocuticular junctions. Two populations of myocytes were detected, the cytoplasm of
one more electron-dense than the other. The only previous report of myofibrilogenesis in invertebrate embryos had described
novel mechanisms. InDrosophila embryonic material, however, the sequence of myofibrilogenesis resembled that in post-embryonic insect or vertebrate material.
Mrs. Pilar Toribio-Fiorio provided excellent technical assistance, and Patricia Minter, the secretarial expertise.
This investigation was supported, in part, by NIH Grant NS9330 and the James Douglas Research Fund to Robert L. Seecof and
NIH Grant No. 1 RO1 CA17223-01 to Raymond L. Teplitz. 相似文献
29.
The floral morphology of seven Oxypetalum species and, in particular, the spatial relationship between the five stigmatic chambers and two separate ovaries of their
flowers with respect to transmission of the pollen tube are studied. In all species, except O. banksii subsp. banksii, floral morphology is similar to that in other Asclepiadeae, and the flowers pollinated with one pollinium develop only one
follicle, which means compitum absence. In O. banksii subsp. banksii flowers, the secretory interstaminal tissue lines the inner walls of the stigmatic chambers as in the other species studied,
but it also reaches the upper part of the inner surface of the filament tube, where it surrounds the styles, an unprecedented
feature for Asclepiadaceae. This tissue secretes nectar and mucilage; the latter acts as transmitting medium for the growth
of pollen tubes from pollinia inserted and hydrated in stigmatic chambers (“hyperstigmas”). Mucilage also functions as an
extragynoecial compitum: in flowers pollinated with one pollinium both carpels develop into a follicle.
Received August 28, 2001; accepted April 9, 2002 Published online: October 14, 2002
Addresses of the authors: Milene Faria Vieira (e-mail: mfvieira@mail.ufv.br), Departamento de Biologia Vegetal, Universidade
Federal de Vi?osa, 36571-000, Vi?osa, Minas Gerais, Brazil. George John Shepherd, Departamento de Botanica, Instituto de Biologia,
Universidade Estadual de Campinas, C.P. 6109, 13083-970, Campinas, S?o Paulo, Brazil. 相似文献
30.
The species Proceratophrys cristiceps belongs to the genus Proceratophrys within the family Cycloramphidae. These amphibians are found exclusively in South America in the morphoclimatic domain of the semi-arid depression zones in northeastern Brazil known as the Caatinga. We examined intrapopulational variation using univariate and multivariate statistics with traditional and geometric morphometrics, which supported the existence of two morphotypes of this species. Our results indicated significant degrees of variation in skeletal characteristics between some natural populations of this species. Careful analyses of variability levels are fundamental to avoid taxonomic errors, principally in populations that demonstrate characteristics intimately associated with their area of occurrence, as is the case of Proceratophrys cristiceps. 相似文献