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11.
D. Menzel 《Protoplasma》1986,134(1):30-42
Summary The cytoskeleton in the siphonous, marine green algaAcetabularia is visualized by immunocytochemistry using antibodies against plant alfa tubulin and animal smooth muscle actin. In the vegetative phase of the life cycle, when the cell grows a cylindrical stalk and until the reproductive cap is completed, actin forms continuous, parallel bundles that extend through the entire length of the stalk and cap rays respectively. Microtubules (MTs) cannot be detected until the primary nucleus, located in the rhizoid of the giant cell, divides to form thousands of secondary nuclei. MTs can then be seen radiating from each secondary nucleus that is encountered in the stalk on its migration upwards into the cap rays. They are oriented mostly parallel to the long axis of the cell. At arrival in the cap rays up to the white spot stage, when nuclei assume equidistant positions in the cap ray cytoplasm, a radiating system of MTs forms around each nucleus and dramatically increases until impressive radial arrays have developed. This phase coincides with a disappearance of actin bundles in the cap rays, but they are retained in the stalk cytoplasm. Shortly after that additional MTs appear around the disk like partitions of cap ray cytoplasm. Concomitantly, bundles of actin reappear colinearly with the circumferrential MTs eventually forming complete rings around each disk of cap ray cytoplasm. During this process the compartments of the future cysts are gradually bulging outwards and simultaneously the rings of actin sink inwards until domes are formed with the nuclei fixed in the top centers of the domes. At this stage the peripheral areas of the radiating MT systems around the nuclei start to break down, whereas the circumferrential MT systems remain intact. Subsequently, the rings of both actin and MTs decrease in diameter, and finally contract to a spot opposite the nucleus, while the cysts continue to develop their oval shape. After the cysts have become separated, they round up and enter several rounds of nuclear divisions. MTs form short radial arrays around each nucleus with minor changes due to a reduction of MTs during division followed by a reappearance after completion of each division. Actin is rearranged in the cysts to a cortical network of randomly oriented, short bundles, that is maintained until gamete formation sets in.These findings accentuate the involvement of Cytoskeletal elements in the key steps of morphogenesis inAcetabularia to an extent that is unknown in higher plants. 相似文献
12.
R. Menzel D. F. Ventura H. Hertel J. M. de Souza U. Greggers 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1986,158(2):165-177
Summary Three different methods were used to determine the spectral sensitivity of retinula cells in the compound eyes of three species of hymenopteran insects (Apis mellifera, Melipona quadrifasciata, Osmia rufa). The conventional flash method gives the least reliable results. Sensitivity is extremely sensitive to small fluctuations of the resting potential and long lasting changes induced by preceding test flashes. The ramp method, which speeds up a spectral scan to about 1 min and keeps effective illumination constant at every flash, determines S() much more reliably. The best results are obtained with the spectral scan method, which provides the experimenter with aS() function of high spectral resolution within 20 s. Using this method we demonstrate that the high observed variability inS() of individual receptors is the result of the inadequacy of the flash method, which was the only method used in earlier studies.Double microelectrode experiments and variations of the stimulus conditions reveal that field potentials and return flow of electric current produced by activated neighboring cells have no effect in the bee eye. We conclude that the model of Shaw (1975, 1981) of current flow in the locust and fly eye does not apply to the bee eye. Very rare recordings (about 1%) of UV receptors with hyperpolarizing responses to long wavelength light are interpreted as having a synaptic inhibitory connection to green receptors.The improvement of spectral measurements of single receptors allows us for the first time to model the spectral input to a color-coding network with great precision. 相似文献
13.
Seventeen species ofHibiscus sectionFurcaria are native to the New World, of which 12 (one diploid, nine tetraploids, one octoploid and one decaploid) have been studied cytotaxonomically. New chromosome counts (2n=4x=72) are reported forH. cucurbitaceus, H. flagelliformis, H. kitaibelifolius, andH. laxiflorus. Seventeen types of tetraploid interspecific hybrids (seven new to this study) all showed complete meiotic chromosome homology (genome formulaGGPP) and normal floral development. That all hybrids were nevertheless almost completely sterile suggests a cytoplasmic component to the genetic differentiation of the species. The diversification of the tetraploid species in habits, habitats and geographical ranges is considerable, despite their similar genome constitutions. A key to 17 native and four introduced African species is presented.Hibiscus cerradoensis sp. nov. is described. 相似文献
14.
DNA gyrase is the bacterial enzyme responsible for converting circular DNA to a negatively supercoiled form. We show that the synthesis of DNA gyrase is itself controlled by DNA supercoiling; synthesis is highest when the DNA template is relaxed. The rates of synthesis in vivo of both the A and B subunits of DNA gyase are increased up to 10-fold by treatments that block DNA gyrase activity and decrease the supercoiling of intracellular DNA. Similarly, efficient synthesis of both gyrase subunits in a cell-free S-30 extract depends on keeping the closed circular DNA template in a relaxed conformation. The results suggest that DNA supercoiling in E. coli is controlled by a homeostatic mechanism. Synthesis of the RecA protein and several other proteins is also increased by treatments that relax intracellular DNA. 相似文献
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16.
Menzel, Margaret Y. (Florida State U., Tallahassee), and F. D. Wilson. Cytotaxonomy of twelve species of Hibiscus section Furcaria. Amer. Jour. Bot. 50(3): 262–271. Illus. 1963.—Metaphase-I chromosome numbers and pairing in 88 accessions showed that H. cannabinus, H. costatus, and H. surattensis are diploid (n = 18); and H. acetosella, H. aculeatus, H. bifurcatus, H.furcellatus, H. meeusei, H. radiatus, H. rostellatus and H. sabdariffa are tetraploid (n = 36), with similar low multivalent frequencies, hence probably allotetraploids each combining 2 well-differentiated genomes. No intraspecific variation in ploidy was found. Fertile, vigorous F1 hybrids between H.furcellatus and H. bifurcatus showed complete chromosome pairing (n = 36), confirming a close relationship between the parents. Two African strains of H. diversifolius were octoploid (n = 72) with low multivalent frequency and hence probably contain 4 differentiated genomes. At least 4, perhaps 5 or 6, differentiated genome groups are represented in tropical Africa, and at least 2 in the American tropics. 相似文献
17.
Chromosome pairing was studied in the following hybrids: Hibiscus radiatus-meeusei (tetraploid F1), H. sabdariffa-meeusei (tetraploid F1 and spontaneous allooctoploid F2), and hexaploid H. acetosella-(sabdariffa-meeusei). Genome constitutions of the species adduced from these data are symbolized as follows: H. radiatus and H. acetosella, AABB; H. meeusei, AAXX; H.sabdariffa, XXYY or AAYY. 相似文献
18.
Detection of coloured stimuli by honeybees: minimum visual angles and receptor specific contrasts 总被引:13,自引:0,他引:13
M. Giurfa M. Vorobyev P. Kevan R. Menzel 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1996,178(5):699-709
Honeybees Apis mellifera were trained to distinguish between the presence and the absence of a rewarded coloured spot, presented on a vertical, achromatic plane in a Y-maze. They were subsequently tested with different subtended visual angles of that spot, generated by different disk diameters and different distances from the decision point in the device. Bees were trained easily to detect bee-chromatic colours, but not an achromatic one. Chromatic contrast was not the only parameter allowing learning and, therefore, detection:
min, the subtended visual angle at which the bees detect a given stimulus with a probability P
0 = 0.6, was 5° for stimuli presenting both chromatic contrast and contrast for the green photoreceptors [i.e. excitation difference in the green photoreceptors, between target and background (green contrast)], and 15° for stimuli presenting chromatic but no green contrast. Our results suggest that green contrast can be utilized for target detection if target recognition has been established by means of the colour vision system. The green-contrast signal would be used as a far-distance signal for flower detection. This signal would always be detected before chromatic contrast during an approach flight and would be learned in compound with chromatic contrast, in a facilitation-like process. 相似文献
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