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51.
Ultrastructural and histochemical studies on guard cells 总被引:6,自引:0,他引:6
Serial thick sections of guard cells from Vicia faba L., Nicotiana tabacum L., Allium cepa L., Zea mays L. and Beta vulgaris L. were obtained systematically (600–800 nm) and viewed with the transmission electron microscope in an effort to demonstrate the presence or absence of a symplastic transport pathway within the stomatal complex. Eight to ten stomata from each species were examined, and no continuous plasmodesmata were found connecting guard cells to sister guard cells or to adjacent epidermal or subsidiary cells. Continuous plasmodesmata were observed in immature guard cells, but were sealed (truncated) during the development of the mature cell wall. Histochemical stains, phosphotungstic acid and silver methenamine, were used to demonstrate differentiation within the mature guard-cell wall. The structural differentiation of the stomatal apoplastic region is discussed in relation to fanctional specialization. Plasma-membrane elaborations or plasmalemmasomes were identified in the guard cells of Zea, and it is suggested that these structures may function in ion transport.Abbreviations PTA-HCl
phosphotungstic acid and hydrochloric acid
- SM
silver methenamine
- UA-LC
uranyl acetate and lead citrate 相似文献
52.
53.
J. del Mazo J. A. Abrisqueta Amalia Pérez-Castillo V. Aller M. Angeles Martín Lucas M. Luisa de Torres M. José Martín 《Human genetics》1978,44(1):105-108
Summary A new case of ring chromosome 4 in a 2-day-old female child with multiple malformations is described. By means of the GTG-banding technique, a karyotype 46,XX,r(4), (p16q35) was determined. The characteristics of the child's karyotype and the relationship with the structure of the chromosome, especially the location of the deletion that produces the syndrome, are compared with previous reports. 相似文献
54.
Characterization and in vitro translation of polyadenylated messenger ribonucleic acid from Neurospora crassa. 总被引:3,自引:0,他引:3
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Ribonucleic acid (RNA) extracted from Neurospora crassa has been fractionated by oligodeoxythymidylic acid [oligo(dT)]-cellulose chromatography into polyadenylated messenger RNA [poly(A) mRNA] and unbound RNA. The poly(A) mRNA, which comprises approximately 1.7% of the total cellular RNA, was further characterized by Sepharose 4B chromatography and polyacrylamide gel electrophoresis. Both techniques showed that the poly(A) mRNA was heterodisperse in size, with an average molecular weight similar to that of 17S ribosomal RNA (rRNA). The poly(A) segments isolated from the poly(A) mRNA were relatively short, with three major size classes of 30, 55, and 70 nucleotides. Gel electrophoresis of the non-poly(A) RNA indicated that it contained primarily rRNA and 4S RNA. The optimal conditions were determined for the translation of Neurospora mRNA in a cell-free wheat germ protein-synthesizing system. Poly(A) mRNA stimulated the incorporation of [14C]leucine into polypeptides ranging in size from 10,000 to 100,000 daltons. The RNA that did not bind to oligo(dT)-cellulose also stimulated the incorporation of [14C]leucine, indicating that this fraction contains a significant concentration of mRNA which has either no poly(A) or very short poly(A) segments. In addition, the translation of both poly(A) mRNA and unbound mRNA was inhibited by 7-methylguanosine-5'-monophosphate (m7G5'p). This is preliminary evidence for the existence of a 5'-RNA "cap" on Neurospora mRNA. 相似文献
55.
Internodal and whorl (branch) cells of the green alga,Chara corallina Klein ex Willd., em. R.D.W., were studied with the extracellular vibrating probe for measuring transmembrane ion currents, and with an extracellular pH microprobe for measuring the surface pH profile. Bands of positive inward current (OH- efflux) 1–3 mm wide were separated by wider bands of outward current (HCO
3
-
influx) along the length of the cell. The measured peaks of inward current ranged from 20 to 60 A cm-2 (98 m from the cell surface) which would correspond to a surface ionic flux of 270–800 pmol cm-2 s-1. The peaks of outward current (HCO
3
-
influx) ranged from 10 to 30 A cm-2 which would correspond to a surface ionic flux of 140–400 pmol cm-2 s-1. The inward current bands matched the regions of surface alkalinity very well. The outward current (HCO
3
-
influx) was reduced at least 10-fold in low-HCO
3
-
medium, with a commensurate readjustment in the strength and pattern of inward current (OH- efflux). (Although these experiments involved a manipulation of the external pH, it is felt that the main adjustment in current patterns was in response to the reduction in exogenous HCO
3
-
). The presence of the vibrating probe perturbed the inward current region when vibrating with a 26-m amplitude, but this perturbation was eliminated when a 7-m amplitude was used. The perturbation was usually observed as a reduction in the number of inward current peaks with an increase (approximate doubling) in the amplitudes of the one or two remaining peaks. Both the inward and outward currents were light-dependent, falling off within seconds of light removal. 相似文献
56.
Polymorphonuclear leukocyte-mediated, antibody-dependent, cellular cytotoxicity against tumor cells: dependence on oxygen and the respiratory burst. 总被引:10,自引:0,他引:10
Experiments were done to determine 1) whether the respiratory burst of superoxide anion (O2-) production in polymorphonuclear leukocytes (PMN) is triggered during antibody-dependent killing of tumor cells and 2) whether O2- production is essential for cytotoxicity. Three parameters of the respiratory burst (1-14C-glucose oxidation, oxygen consumption, and O2- release) were increased 2.5- to 7.3-fold during killing of antibody-primed tumor cells by human PMN. Added catalase and superoxide dismutase did not inhibit lysis, possibly because these enzymes were unable to diffuse into the inter-plasma-membrane space between killer and target cells. Evidence for an O2- requirement for cytotoxicity was the fact that concentrations of amobarbital or phenylbutazone sufficient to inhibit the cyanide-insensitive respiration of PMN also inhibited cytotoxicity. Also, hypoxic conditions inhibited cytotoxicity from 29 to 73%. The requirement for oxygen was most likely related to O2- generation and not mitochondrial respiration since cyanide and azide, which inhibit mitochondrial respiration, increased cytotoxicity. 相似文献
57.
Lucas WJ 《Plant physiology》1979,63(2):248-254
The nature of the transport system responsible for the establishment of alkaline bands on cells of Chara corallina was investigated. The transport process was found to be insensitive to external pH, provided the value was above a certain threshold. At this threshold (pH 5.1 to 4.8) the transport process was inactivated. Transport function could be recovered by raising the pH value of the external solution. The fastest rate of recovery was always obtained in the presence of exogenous HCO3−. 相似文献
58.
An analysis of canine size and jaw shape in some Old and New World non-human primates 总被引:1,自引:0,他引:1
P. W. Lucas 《Journal of Zoology》1981,195(4):437-448
An analysis of the relationship between the height of canine teeth, the length of the jaw and the height of the jaw joint above the occlusal plane was undertaken in catarrhine primates and some cebids. An inverse relationship was found in males between the angle
the jaw must be opened to clear the canine teeth and the height of the jaw joint above the occlusal plane, divided by the length of the lower jaw. A theoretical model is presented which can account for this phenomenon and which presumes selection pressure for alignment of the canine teeth when in use. In females, the angle the jaw must be opened to clear
the canine teeth was in most cases very small though in certain species elongated canines
were found. 相似文献
the jaw must be opened to clear the canine teeth and the height of the jaw joint above the occlusal plane, divided by the length of the lower jaw. A theoretical model is presented which can account for this phenomenon and which presumes selection pressure for alignment of the canine teeth when in use. In females, the angle the jaw must be opened to clear
the canine teeth was in most cases very small though in certain species elongated canines
were found. 相似文献
59.
W. J. Criddle J. C. Fry Maureen M. Keaney C. M. Lucas J. A. Tovey 《Molecular and cellular biochemistry》1977,16(1):3-8
Summary Experimental studies have been undertaken with a view to isolation of the enzyme(s) responsible for the stereospecific oxidation of myo-inositol. A partial fractionation has been achieved and the properties of this extract examined. Results show that the active enzyme may well have a cytochrome component and there is indication that the stereospecificity ofAcetomonas oxydans results from permease as opposed to dehydrogenase activity. Kinetic experiments suggest that only one type of active enzyme site is involved in the dehydrogenation of myo-inositol.Departments of Chemistry and Applied Biology 相似文献
60.
A study was performed to establish the value of immune adherence haemagglutination tests for antibody to hepatitis A virus in the diagnosis of non-B hepatitis. Infection with hepatitis A virus was confirmed in 14 out of 16 patients from six families and seven out of nine patients in whom the source of infection was unknown. One additional patient, who had had two episodes of jaundice, was shown to have had an attack of hepatitis A followed by an attack of hepatitis B. In patients with acute hepatitis A antibody detectable by immune adherence haemagglutination becomes detectable three or four weeks after the onset of symptoms and reaches peak levels about five weeks later. 相似文献