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41.
Cytokinin requiring cells of Nicotiana tabacum L. cv "Havana 425" can be induced in culture to become cytokinin autotrophic. This process is known as cytokinin habituation. Earlier we showed that pith parenchyma tissue consists of inducible cells, which habituate at high rates when treated with cytokinin, and noninducible cells, which remain cytokinin requiring under these conditions. The inducible and noninducible phenotypes are determined states that arise during the development of the tobacco plant and are inherited by individual cells. Here we show that pith tissue of plants regenerated from cloned lines of noninducible cells exhibits the inducible phenotype indicating that noninducible cells, or their descendants, can become inducible. This change in competence for habituation appears to have an epigenetic basis; it is reversible, occurs at high rates, and depends on the developmental state of the cells. The habituated state occurs in two forms that can be distinguished by their difference in developmental potential. Habituated cells derived from inducible pith cells give rise to normal plants whose leaf and pith tissues require cytokinin for growth in culture. In contrast, habituated cells obtained by transferring noninducible cells on media with progressively lower cytokinin concentrations give rise to plants whose leaf and pith tissues exhibit a cytokinin-habituated phenotype in culture. 相似文献
42.
43.
Quinolinic Acid Phosphoribosyltransferase in Rat Brain 总被引:9,自引:7,他引:2
Because of the possible participation of quinolinic acid in brain function and/or dysfunction, the characteristics of its catabolic enzyme, quinolinic acid phosphoribosyltransferase (QPRTase; EC 2.4.2.19), were examined in rat brain tissue. For this purpose, a sensitive radiochemical assay method, based on the conversion of quinolinic acid to nicotinic acid mononucleotide (NAMN), was developed. For brain QPRTase, the Mg2+ dependency, substrate specificity, and optimal assay conditions were virtually identical to those of the liver enzyme. Kinetic analyses of brain QPRTase revealed a Km of 3.17 +/- 0.30 microM for quinolinic acid and Km = 65.13 +/- 13.74 microM for the cosubstrate phosphoribosylpyrophosphate. The respective Vmax values were: 0.91 +/- 0.08 pmol NAMN/h/mg tissue for quinolinic acid and 11.65 +/- 1.55 fmol NAMN/h/mg tissue for phosphoribosylpyrophosphate. All kinetic parameters measured for the brain enzyme were significantly different from those determined for liver QPRTase, indicating structural differences or distinct regulatory processes for the brain and liver enzymes. Phthalic acid was a potent competitive inhibitor of brain QPRTase. Examination of the regional distribution of QPRTase in the rat CNS and retina indicated a greater than 20-fold difference between the area displaying the highest activity (olfactory bulb) and those of only moderate activity (frontal cortex, striatum, retina, hippo-campus). Enzyme activity was present at the earliest age tested, 2 days, and tended to increase in older animals. Brain QPRTase activity was preferentially located in the nerve-ending (synaptosomal) fraction. Enzyme activity was stable over extensive periods of storage at -80 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
44.
Activation of the transformation potential of the cellular fps gene 总被引:27,自引:0,他引:27
Chicken cellular-fps (c-fps) sequences were substituted for viral-fps (v-fps) sequences in two retroviral genome structures, one that expressed a c-fps gene product that was indistinguishable from the normal c-fps gene product expressed in chicken bone marrow cells, and another that expressed a gag-fps fusion protein. When c-fps gene sequences (without linked gag gene sequences) were expressed at high levels in a viral vector, no transformation of fibroblasts was detected. It was previously demonstrated that the corresponding v-fps sequences could transform fibroblasts. When the same c-fps sequences were expressed in a form linked to gag gene sequences, transformation of fibroblasts and induction of tumors were observed. The data suggest that the c-fps gene product lacks transformation potential by itself even when overexpressed and that the transformation potential of the c-fps gene can be activated by either mutation (or mutations) in the fps coding region or by fusion with viral gag gene sequences. 相似文献
45.
Localization of Tamm-Horsfall-glycoprotein-like immunoreactivity in cultured baby-hamster kidney cells, shown by immunofluorescence and by light- and electron-microscopic immunoperoxidase techniques.
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Tamm-Horsfall glycoprotein was isolated from hamster urine, and antiserum against it was produced in rabbits. IgG was isolated from the antiserum. Immunocytochemical methods were used to localize Tamm-Horsfall-like immunoreactivity in three substrains of baby-hamster kidney (BHK) cells. Indirect immunofluorescence techniques showed that, in two substrains (BHK-21/C13/2P and BHK-21/C13/3P), a proportion of the cells fluoresced brilliantly, whereas those of the third substrain (BHK-21/ICRF) were totally negative. Related findings were obtained by the immunoperoxidase optical-microscopic technique. From the results of immunoperoxidase techniques using the electron microscope, it was concluded that the substance was present in association with the plasma membranes of the reacting cells. Our data suggest that the line of baby-hamster kidney cells, BHK-21/C13, may contain cells of renal-tubular epithelial origin, and that the proportion of these may be variable from one subculture to another. 相似文献
46.
The involvement of a rhodopsin-like photopigment in the photoperiodic response of the Japanese quail
R. G. Foster B. K. Follett 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1985,157(4):519-528
Summary A technique has been developed for the investigation of the photopigment involved in the photoperiodic control of reproduction in Japanese quail,Coturnix coturnix. When these photoreceptors were exposed to white or monochromatic light a clear relationship was found between light intensity and the extent of photo-induced luteinizing hormone (LH) secretion. A spectroradiometric investigation of the passage of light through the skull and brain enabled us to illuminate the hypothalamic region with equal numbers of photons at a range of wavelengths. Action spectra were then conducted and showed a photopigment with a peak sensitivity at wavelengths near 500 nm. An excellent match was obtained when the standard absorption spectrum for a rhodopsin was fitted to the action spectrum, suggesting a rhodopsin maximally sensitive at 492 nm. The absolute sensitivity of the photoreceptors was calculated at a range of wavelengths: with light at 500 nm, 2.85×10–12 E·cm–2·s–1 triggered the photoperiodic response. This level of sensitivity is matched only by the rhodopsin visual pigments.Abbreviations
LH
luteinizing hormone
-
T
transmission 相似文献
47.
Basement membrane components in healing rabbit corneal epithelial wounds: immunofluorescence and ultrastructural studies 总被引:10,自引:3,他引:7
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The nature of the substrate that supports epithelial migration in vivo is of interest, particularly with respect to mechanisms of wound healing. Immunofluorescence and electron microscopy were used to search for common substrate components in prototype rabbit corneal wounds: epithelial scrape wounds, in which the corneal or conjunctival epithelium migrated over the denuded lamina densa of the corneal basement membrane (CBM), and superficial keratectomy, in which the corneal epithelium migrated over a bare stroma without CBM. The corneal epithelium moved rapidly over the CBM or stroma to cover the defect within 2-3 d, whereas the conjunctival epithelium required 1-2 wk. In all wounds, fibronectin and fibrin/fibrinogen were deposited onto the bare surface within 8 h after wounding and persisted under the migrating epithelium until migration was complete. Bullous pemphigoid antigen (BPA), a normal component of the CBM, was removed with the epithelium upon scrape wounding and reappeared in the CBM after migration was completed. In contrast, the conjunctival epithelium had a continuous subepithelial band of BPA out to the migrating tip. Laminin, also a normal component of the CBM, was not removed in the scrape wounds, indicating that the region of least resistance to shear stress was between the BPA and laminin layers. Laminin was removed by superficial keratectomy and was not detectable under the leading edge of the migrating cells. Laminin and BPA were restored in the CBM by 2-4 wk. Type IV collagen could not be detected in normal CBM, but was conspicuously present in conjunctival basement membrane and in blood vessels. Focal bands of type IV collagen did appear in the newly synthesized CBM 2-4 wk after keratectomy. These results argue that BPA, laminin, and type IV collagen are not essential for the migration of corneal epithelium during wound healing and support the hypothesis that fibronectin and fibrin/fibrinogen are the common, perhaps the essential, components of the provisional matrix that serves as a substrate until the permanent attachment components are regenerated. 相似文献
48.
The development and testing of an integrated kinetic model describing both short and long term zinc metabolism in humans is discussed. The development took place in two stages. The first, based on a five day turnover study, details the early phases of zinc metabolism in several body tissues together with absorption and excretion. This model, however, accounts for only 10% of total body zinc. To describe the kinetics of total body zinc, a long term model which contains a reduced version of the five day model was developed. This model required an additional compartment for the liver system, but as postulated in the short term model, 90% of body zinc turns over slowly in a single compartment. The models are then used to describe the effect on zinc metabolism of different disease states and lietary perturbations. These additional studies enhance the models' validity while providing physiological insights. 相似文献
49.
Effect of age and training on aerobic capacity and body composition of master athletes 总被引:5,自引:0,他引:5
Pollock M. L.; Foster C.; Knapp D.; Rod J. L.; Schmidt D. H. 《Journal of applied physiology》1987,62(2):725-731
Maximum oxygen uptake (VO2max) and body composition have been shown to deteriorate with age. How much of the decline is attributable to aging and how much is affected by reduced physical activity is not known. The purpose of this investigation was to determine the aerobic capacity and body composition of 24 master track athletes and to evaluate the relationship to age and maintenance of training over a 10-yr period. The subjects (50-82 yr of age) were retested after a 10.1-yr follow-up (T2). All continued their aerobic training, but only 11 were still highly competitive (COMP) and continued to train at the same intensity. The other 13 athletes studied became noncompetitive (post-COMP) and reduced their training intensity. The results showed the COMP group to maintain its VO2max and maximum O2 pulse while the post-COMP group showed a significant decline (54.2-53.3 vs. 52.5-45.9 ml X kg-1 X min-1; 20.7-20.8 vs. 22.4-20.0 ml/beat from test one (T1) to T2 for the COMP vs. post-COMP groups, respectively). Maximum heart rate declined 7 beats/min for both groups. Body composition showed no difference between groups from T1 to T2. For both groups body weight declined slightly (70.0-68.9 kg), percent fat increased significantly (13.1-15.1%), and fat-free weight decreased significantly (61.0-59.0 kg). Thus, when training was maintained, aerobic capacity remained unchanged over the follow-up period. Body composition changed for both groups and may have been related to aging and/or the type of training performed. 相似文献
50.
In previous experiments two extreme modes of visual discrimination performance have been investigated by measuring small differences in pattern shape at points along a continuum of pattern shapes. These two modes, associated with discrete and continuous encoding processes, were obtained by simultaneously manipulating the number of pattern components in the display and the effective duration of the display. In this experiment, discrimination performance was measured for a fixed number of pattern components, namely three, and variable display time course. The stimuli used were curved lines drawn from a continuum with curvature parameter s. There were three stimulus time courses: (1) 2-s stimulus display, (2) 100-ms stimulus display, and (3) 100-ms stimulus display followed by a post-stimulus mask. Discrimination performance declined smoothly and monotonically with s for (1), but varied non-monotonically with s revealing a central peak for (3). Performance for (2) was intermediate between that for (1) and that for (3). A reduction in effective stimulus duration alone was thus sufficient to cause a transition from continuous to discrete modes of discrimination performance, a result which may be compatible with an explanation of variable discrimination modes based on a method of successive internal approximations of the stimulus. 相似文献