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221.
Summary In this report we show that large cytoplasmic channels form between the tapetal cells ofZea mays (maize) during the period of tapetal cell differentiation. Tapetal cells are connected by plasmodesmata through their cellulosic cell walls prior to the first meiotic division of the meiocytes. As the tapetal cellulose wall is degraded at the onset of meiosis, both plasmodesmata and cytoplasmic channels measuring 50–200 nm are detectable between tapetal cells. By the time the meiotic tetrad is formed, the cytoplasmic channels are well-established and vary in size from 100–400 nm. The channels, with an average diameter of 200–300 nm, persist after the microspores are released from the callose wall and throughout the period of exine development in microsporogenesis. The channels could potentially allow for free exchange of cytoplasm and organelles. As the tapetal cells begin to pull apart and become vacuolate prior to microspore mitosis, the connecting channels are no longer detectable. 相似文献
222.
Patricia Maurer Corinne Royer Bernard Mauchamp Patrick Porcheron Danile Debieu Guy Riba 《Archives of insect biochemistry and physiology》1991,16(1):1-9
The major ecdysteroids in large worker pupae of the leaf-cutting ant Acromyrmex octospinosus were characterized at the peak ecdysteroid concentration by using high-performance liquid chromatography, enzyme immunoassay, and mass spectrometry. In decreasing amounts, they were determined to be makisterone A, an unidentified C28 ecdysteroid bearing a molecular weight of 494, 20-hydroxyecdysone (ratio of 1 to 6 as compared to makisterone A), and putative but negligible ecdysone. The presence of both C28 and C27 ecdysteroids is discussed in relation to the content of 4-desmethylsterols determined by gas chromatography and mass spectrometry to be ergosta-5,7,24 (28)-trien-3β-ol, ergosterol, ergosta-5,7-dien-3β-ol and ergosta-7,24(28)-dien-3β-ol for the main sterols, and with a small amount of cholesterol. 相似文献
223.
This paper concerns an enzymological investigation into a putative canine canalogue of the human autosomal recesive disease primary hyperoxaluria type 1 (alanine:glyoxylate / serine:pyruvate aminotransferase deficiency). The liver and kidney activities of alanine:glyoxylate aminotransferase and seribe:pyruvate aminotransferase in two Tibetan Spaniel pups with familial oxalate nephripathy were markedly reduced when compared with a variety of controls. There were no obvious deficiencies in a number of other enzymes including d-glycerate dehydrogenese / glyoxylate reductase which have been shown previously to be deficient in primary hyperoxaluria type 2. Immunoblotting of liver and kidney homogenates from oxalotic dogs also demonstrated a severe deficiency of immunoreactive alanine:glyoxylate aminotransferase. The developmental expression of alanine:glyoxylate / serine:pyruvate aminotransferase was studied in the livers and kidneys of control dogs. In the liver, enzyme activity and immunoreactive protein were virtually undetectable at 1 day old, but then increased to reach a plateau between 4 and 12 weeks. During this period the activity was similar to that found in normal humanb liver. The enzyme activities and the levels of immunoreactive protein in the kidneys were more erratic, but they appeared to increase up to 8 weeks and then decrease, so that by 36 weeks the levels were similar to those found at 1 day. The data presented in this paper suggest that these oxalotic dogs have a genetic condition that is anlogous, at least enzymologically, to the human disease primary hyperoxaluria type 1. 相似文献
224.
Kim B. Saunders Patricia A. D’Amore 《In vitro cellular & developmental biology. Animal》1992,28(7-8):521-528
Summary Heterotypic cell-cell interactions appear to be involved in the control of development and function in a wide variety of tissues.
In the vasculature, endothelial cells and mural cells (smooth muscle cells or pericytes) make frequent contacts, suggesting
a role for intercellular interactions in the regulation of vascular growth and function. We have previously grown endothelial
cells and mural cells together in mixed cultures and found that heterocellular contact led to endothelial growth inhibition.
However, this mixed culture system does not lend itself to the examination of the effects of contact on the phenotype of the
individual cell types. We have therefore developed a co-culture system in which cells can be co-cultured across a porous membrane,
permitting intercellular contact while maintaining pure cell populations. Co-culture of endothelial cells and smooth muscle
cells across membranes with pore sizes of 0.02, 0.4, 0.6, and 0.8μm maintained the two cell types as homogeneous populations, whereas smooth muscle cells migrated across the membrane through
pores of 2.0μm. Vascular cell co-culture across membranes with 0.8-μm pores resulted the inhibition of endothelial cell proliferation and the generation of conditioned media which inhibited
endothelial cell growth. The arrangement of the cells in this co-culture system mimics thein vivo orientation of vascular cells in which mural cells are separated from the abluminal surface of the endothelium by a fenestrated
internal elastic lamina or basement membrane. Because this co-culture system maintains separable populations of cells in contact
or close proximity allowing for biochemical and molecular analyses of pure populations, it should prove useful for the study
of cell-cell interactions in a variety of systems. 相似文献
225.
Somatic embryogenesis in soybean via somatic embryo cycling 总被引:4,自引:0,他引:4
Wennuan Liu Patricia J. Moore Glenn B. Collins 《In vitro cellular & developmental biology. Plant》1992,28(3):153-160
Summary The objectives of the present research were: a) to develop an efficient soybean embryogenic regeneration system characterized
by a high frequency of explant response and a large number of somatic embryos per explant; b) to evaluate the factors affecting
somatic embryogenesis via somatic embryo cycling; and c) to identify the origin of somatic embryos in the system. A highly
improved and efficient system for soybean somatic embryogenesis was established using somatic embryo cotyledons and somatic
embryo hypocotyl/radicle explants plated on α-naphthaleneacetic acid (NAA) or 2,4-dichlorophenoxyacetic acid (2,4-D) supplemented
MS basal media. The system included somatic embryo cycling between liquid and solid medium and it consistently gave rise to
a much higher frequency of explant response and a larger number of embryos per responding explant than those obtained from
zygotic cotyledon explant tissues. Genotype, differences were observed for response in some of the treatments with cv “Fayette”
being more responsive than “J103”. Histological studies revealed that somatic embryos induced in the somatic embryo cycling
system originated almost exclusively from epidermal cells on both 2,4-D and NAA inductive media. The cells of the epidermis
proliferated to produce somatic embryos directly without an intervening callus phase. A single-cell origin of somatic embryos
was observed in cultures on a 40 mg/liter 2,4-D treatment. A large number of responding cells in the epidermis was also observed
in the 10 mg/liter NAA treatment. The single-cell origin of somatic embryos from epidermal layers of the explant tissues should
facilitate development of an efficient transformation system for soybean. 相似文献
226.
227.
Patricia Arevalo-Durup 《BioControl》1992,37(2):239-247
Les interactions h?te-parasito?de ont été abordées dans le cas du systèmeTrichomalopsis peregrina G. (Pteromalidae) et son h?te grégaireEuproctis chrysorrhoea L. (Lymantriidae), au cours de la phase diapausante des chenilles dans les nids d'hiver tissés par ce ravageur. Un échantillon de 1 432 nids
d'hiver a été récolté dans 8 peuplements de chênes dans la région toulousaine durant l'hiver 1988. Le volume du nid a été
utilisé comme estimateur du nombre de chenillesh?tes dans les nids et la réponse du parasito?de a été comparée à celle prévue
par la théorie de la stratégie optimale de recherche. Les principaux résultats sont les suivants:
Host-parasitoid interactions are reviewed in the case ofTrichomalopsis peregrina G. (Pteromalidae) and its aggregated host,Euproctis chrysorrhoea (Lymantriidae) during the arrest of development of the caterpillars in the winter nest spun by this forest pest. A sample of 1,432 winter
nests in 8 oak groves near Toulouse, Haute-Garonne, France were collected during the winter 1988. The volume of the winter
nests has been used to estimate the number of larvae in nests. The response of the parasitoid has been compared with the optimal
searching theory for parasitoids. The main results are:
(i) Parasitoids present an aggregative response; to a higher density of host larvae corresponds a higher number of apparent
attacks; (ii) in contrast with that theory, the apparent rate of parasitism is inversely density dependent with respect to
caterpillar density in the nest; (iii) these results suggest that the access of the parasito?d to the caterpillars is limited
to the proximity of the nest surface. 相似文献
(i) | les parasito?des présentent une réponse agrégative typique, les plus fortes densités d'h?tes correspondant au plus grand nombre de parasito?des sortant des nids; |
(ii) | contrairement à la théorie, les taux de parasitisme apparent varient en sens inverse des effectifs de chenilles par nid; |
(iii) | ces résultats suggèrent l'existence d'une accessibilité limitée des chenilles, l'activité parasitaire s'exer?ant sur les chenilles proches de la surface du nid. |
228.
Lessonia trabeculata is one of the major kelps found along the northern coast of Chile. In addition to its ecological and economic importance, L. trabeculata may be severely affected by environmental disturbances such as El Níño, which during 1982–1983 cleared wide areas along the coast of Peru and Chile. The main goal of this work was to mass culture L. trabeculata and to observe the growth of sporophytes obtained in the laboratory and cultured in the sea. Juvenile sporophytes obtained in the laboratory were attached between 1 and 6 m in depth. The linear growth rate, as blade elongation, was recorded weekly for seven months. No significant differences (p < 0.05) were found in sporophyte blade linear growth at different depths. The best elongation growth rate was 7.5 ± 1.6 mm d–1 at 3 m during March. This preliminary work suggests that L. trabeculata follows an annual growth cycle similar to that of other Laminariales with a high rate of blade elongation during the summer and decreasing towards autumn. This species can be considered a potential candidate for aquaculture to increase the availability of raw material and aid in repopulation of overexploited areas. 相似文献
229.
Purification and Characterization of Echinonectin, a Carbohydrate-Binding Protein from Sea Urchin Eggs 总被引:2,自引:2,他引:0
Patricia A. Veno Margaret A. Strumski William H. Kinsey 《Development, growth & differentiation》1990,32(3):315-319
A galactose-specific carbohydrate binding protein has been identified in eggs and embryos of the sea urchin Lytechinus variegatus . This protein, named echinonectin (Alliegro et al., 1988, J. Cell Biol. 107; 2319–2327) has been described as a cell-substrate adhesion protein functioning during embryonic development. The purified protein has an apparent molecular weight of 220 kDa and exists as a dimer of apparently identical 110 kDa subunits. The carbohytrate specificity of the purified protein was examined through the use of competition assays. The protein has a marked specificity for galactose and fucose and a higher affinity for polymers of galactose or galactose sulfate such as carrageenan. 相似文献
230.
Regulation of amidase formation in mutants from Pseudomonas aeruginosa PAO lacking glutamine synthetase activity 总被引:1,自引:0,他引:1
Dick B. Janssen Patricia M. Herst Han M. L. J. Joosten Chris van der Drift 《Archives of microbiology》1982,131(4):344-346
The formation of amidase was studied in mutants from Pseudomonas aeruginosa PAO lacking glutamine synthetase activity. It appeared that catabolite repression of amidase synthesis by succinate was partially relieved when cellular growth was limited by glutamine. Under these conditions, a correlation between amidase and urease formation was observed. The results suggest that amidase formation in strain PAO is subject to nitrogen control and that glutamine or some compound derived from it mediates the nitrogen repression of amidase. 相似文献