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951.
952.
R. De Boer 《Genetica》1982,58(1):17-22
A case of non-reciprocal hybrid infertility between strains of the spider mite Tetranychus urticae Koch is described. Evidence is presented that the infertility results from an interaction between a chromosomal and a cytoplasmic factor. The presence or absence of the cytoplasmic factor seems to be controlled also by chromosomal genes. 相似文献
953.
A study of the puffing patterns of the Jst, J1, U1–2, U1–2–8 and Ust chromosomal arrangements of Drosophila subobscura, from different geographical origins, has been carried out. Twenty-eight puffs were observed, 10 on the J chromosome, and 18 on the U chromosome. No differences, whether qualitative or quantitative, have been found between the puffing pattern of the J chromosome, whether from the same of different geographical background. In the U chromosome, the U1–2 and U1+2+8 arrangements show the same puffing pattern, and neither quantitative nor qualitative differences were found. However, the puffing pattern of these chromosomes alters considerably in the Ust arrangement of the K228 laboratory strain. 相似文献
954.
A comparative study of the heat resistance ( D 60 values) of four Saccharomyces spp. and two Kluyveromyces spp. (21 strains) showed a 30–350-fold higher heat resistance of ascospores than of vegetative cells. It was also observed that small numbers of ascospores exhibiting a considerably higher heat resistance can easily be formed, even in a complete vegetative growth medium. This phenomenon may have led most other authors to report none or only slight differences between the heat resistance of yeast ascospores and their vegetative cells. Until more information has been collected about the ascospore load of acid (fruit) products and their heat resistance, accurate calculations of the minimum F values for heat preservation of these products may not be possible. 相似文献
955.
H. J. Lindeboom H. A. J. De Klerk-V. D. Driessche A. J. J. Sandee 《Aquatic Ecology》1982,16(1):93-102
Summary During five 28-hours measurements in 1981, the oxygen production and consumption in an eelgrass community in saline Lake Grevelingen were investigated using light plexiglass enclosures. Applying a conversion factor of 0.29 the amount of carbon fixed and the amount of organic carbon mineralized were estimated. Gross and net production were estimated over 24-hours periods.There appeared to be a good correlation between production and insolation on the water surface. For every measurement period the production as a function of light and aboveground eelgrass biomass in the enclosure were calculated. This showed a maximum of 5.10–6 mg C.J.–1 g dry weight–1 in April and minimum of 1.4.10–6 mg C.J.–1 g–1 in August.Using the calculated production coefficients, the insolation and the eelgrass biomass the gross production, net production and consumption during the growing season of 1976 were calculated. Gross production amounted to 340 gC.m–2, and net production came to 130 g C.m–2. Approximately 60 gC.m–2 was respired by the eelgrass plants while the remaining 150 gC.m–2 was consumed or mineralized by other organisms on the sampling spot. Approximately 120 g C.m–2.yr–1 was transported by wind and wave action towards the eastern part of the lake where it became anaerobically degraded. This resulted in the formation of sulfide and methane.Communication no. 236 of the Delta Institute for Hydrobiological Research, Yerseke, The Netherlands. 相似文献
956.
The cytokineplast: purified, stable, and functional motile machinery from human blood polymorphonuclear leukocytes 总被引:11,自引:4,他引:7
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We examined the formation of motile, chemotactically active, anucleate fragments from human blood polymorphonuclear leukocytes (PMN, granulocytes), induced by the brief application of heat. These granule-poor fragments are former protopods (leading fronts, lamellipodia) that become uncoupled from the main body of the cell and leave it, at first with a connecting filament that breaks and seals itself. The usual random orientation of such filaments can be controlled by preorientation of cells in a gradient of the chemotactic peptide, N-formylmethionylleucylphenylalanine (F-Met-Leu-Phe) (2x10(-9) M- 1x10(-8)). Cytochalsin B, 2.5-5 μg/ml, prevents fragment formation; colchicine, 10(-5) M, does not. In scanning electron micrographs, fragments are ruffled and the cell body rounded up and rather smooth. In transmission electron micrographs, fragments contain microfilaments but lack centrioles and microtubules. Like intact cells, both bound and free fragments can respond chemotactically to an erythrocyte destroyed by laser microirradiation (necrotaxis); the free, anucleate fragments may do so repeatedly, even after having been held overnight at ambient temperatures. We propse the name cytokineplast for the result of this self-purification of motile apparatus. The exodus of the motile machinery from the granulocyte requires anchoring of the bulk of the cell to glass and uncoupling, which may involve heat-induced dysfunction of the centrosome. In ultrastructural studies of the centrosomal region after heat, centriolar structure remains intact, but pericentriolar osmiophilic material appears condensed, and microtubules are sparse. These changes are found in all three blood cell types examined: PMN, eosinophil, and monocyte. Of these, the first two make fragments under our conditions; the more sluggish monocyte does not. Uncoupling is further linked to centrosomal dysfunction by the observation that colchicines-treated granulocytes (10(-5)M, to destroy the centrosome’s efferent arm) make fragments after less heat than controls. If motive force and orientation are specified mainly from the organelle-excluding leading front, then endoplasmic streaming in PMN is a catch-up phenomenon, and microtubules do not provide the vector of locomotion but rather stabilize and orient the “baggage” (nucleus, granuloplasm)—i.e., they prevent fishtailing. Moreover, constraints emanating from the centrosome may now be extended to include, maintenance of the motile machinery as an integral part of the cell. 相似文献
957.
Influence of the carboxyl terminus of luteinizing hormone-releasing hormone and bradykinin on hydrolysis by brain endo-oligopeptidases 总被引:1,自引:0,他引:1
A C De Camargo M J Da Fonseca H Caldo K De Morais Carvalho 《The Journal of biological chemistry》1982,257(16):9265-9267
A homogeneous preparation of endo-oligopeptidase A from rabbit brain cleaves luteinizing hormone-releasing hormone (less than Glu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH2) at the Tyr-Gly bond only after the removal of Gly-NH2 from the COOH-terminal position of the molecule. The influence of the carboxyl terminus on hydrolysis by brain endo-oligopeptidases was studied using bradykinin as a model substrate. The substitution of the carboxyl group of bradykinin by the amide reduces by 2.5-fold the rate of Phe-Ser bond hydrolysis by endo-oligopeptidase A but has no effect on the rate of hydrolysis of the Pro-Phe bond by endo-oligopeptidase B. On the other hand, the deletion of Phe-Arg from the COOH-terminal portion of bradykinin makes the peptide resistant to hydrolysis by endo-oligopeptidase A whereas it increases by 5-fold the rate of hydrolysis of the Pro-Gly bond by endo-oligopeptidase B. 相似文献
958.
Field and greenhouse experiments showed that yield losses of sugarbeet, Beta vulgaris, did not occur in soil infested with fewer than eight Heterodera schachtii eggs/g soil. However, larger population densities greatly reduced sugarbeet yield. In the field experiment, the yield in microplots inoculated with more than 64 eggs/g soil was less than 20% of yields in uninoculated microplots. Nevertheless, tolerance limits of 4 and 1.8 eggs/g soil, in greenhouse and field microplots, respectively, were derived by fitting the data with the equation y =m + (l - m)zP-T. Maximum rates of multiplication of 55 and more than 300, and equilibrium densities of 340 and 130 eggs/g soil, were estimated in greenhouse and field microplot tests, respectively. 相似文献
959.
Adenylate Cyclases in the Vertebrate Retina: Distribution and Characteristics in Rabbit and Ground Squirrel 总被引:7,自引:5,他引:2
Adenylate cyclase activity and the effects of EGTA, 5'-guanylylimidodiphosphate (GPP(NH)P), and dopamine were measured in microdissected layers of rod-dominant (rabbit) and cone-dominant (ground squirrel) retinas, The distribution of basal enzyme activity was similar in both species, with the highest levels found in the inner plexiform and photoreceptor cell inner segment layers, EGTA inhibited adenylate cyclase in the inner retina of both species and stimulated activity in rabbit outer and inner segment layers, but had no effect in these layers from ground squirrel. Enzyme activity was stimulated in all regions by GPP(NH)P, except in the outer segments of the photoreceptors. Dopamine stimulated the enzyme in the outer and inner plexiform and inner nuclear layers in rabbit, but only in the inner plexiform layer in ground squirrel. These data demonstrate that the enzymatic characteristics of adenylate cyclase vary extensively from region to region in vertebrate retina and suggest that cyclic AMP may have multiple roles in this tissue. A model for the distribution of the different forms of adenylate cyclase in retina is proposed. 相似文献
960.
M J De Wolf P Vitti F S Ambesi-Impiombato L D Kohn 《The Journal of biological chemistry》1981,256(23):12287-12296
Bovine thyroid membranes possess both ADP ribosyltransferase and NAD glycohydrolase activities with the same Km values for NAD and the same pH optima. In intact membranes, the ADP ribosyltransferase is limited in its extent by the amount of available membrane acceptor which can be ADP-ribosylated; in membranes solubilized with lithium diiodosalicylate, an artificial acceptor, L-arginine methyl ester, can be substituted to eliminate this limitation. The product of the ADP ribosyltransferase is a mono-ADP-ribosylated acceptor whether the intact or solubilized membrane provides the enzyme activity and whether membrane or exogenous acceptor, L-arginine methyl ester, is utilized. The intact membranes and the solubilized preparation also have an enzyme activity which can release AMP from the mono-ADP-ribosylated acceptor whether formed by the action of the membrane ADP ribosyltransferase or the A promoter of cholera toxin. The NAD glycohydrolase activity appears to represent the half-reaction of the ADP ribosyltransferase, i.e. an activity measurable substituting water for a membrane acceptor or L-arginine methyl ester. Membranes from functional rat thyroid cells in culture, i.e. cells chronically stimulated by thyrotropin and unresponsive to further additions of thyrotropin, have low ADP-ribosylation but high NAD glycohydrolase activities. In contrast, membranes from nonfunctional rat thyroid cells, i.e. cells unresponsive to thyrotropin, have high ADP-ribosylation and low NAD glycohydrolase activities. NAD hydrolysis by the NAD glycohydrolase activity cannot account for the low ADP-ribosylation activity in membranes from the functioning cells, and its low level of ADP-ribosylation can be eliminated by solubilizing the membranes and substituting an artificial acceptor, L-arginine methyl ester. The ADP ribosyltransferase activity of rat thyroid cell membrane preparations can be enhanced by thyrotropin in a dose-dependent manner but not by insulin, glucagon, hydrocortisone, adrenocorticotropin, or its glycoprotein hormone analog, human chorionic gonadotropin. It is thus suggested (i) that, in analogy to cholera toxin, thyrotropin-stimulated ADP-ribosylation may be important in the regulation of the adenylate cyclase response and (ii) that the level of membrane acceptor available for ADP-ribosylation may relate both to a stable "'activated" state of the adenylate cyclase system in cells chronically stimulated with thyrotropin and/or to a desensitized state with regard to a failure of more thyrotropin to elicit additional functional responses. 相似文献