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961.
Green plant cells can generate ATP in both chloroplasts and mitochondria. Hence the effect of photosynthesis on dark mitochondrial respiration can be considered at a variety of levels. Turnover of ceitric acid cycle dehydrogenases, which is essential for supply of carbon skeletons for amino acid synthesis, seems to be largely unaffected during photosynthesis. The source of carbon for the anaplerotic function of the citric acid cycle in light is however, not known with certainty. NADH generated in these reactions is probably not oxidised via the mitochondrial electron transfer chain coupled to ATP synthesis. However, it may be oxidised by the alternative cyanide-insensitive pathway, exported to the cytosol via the oxaloacetate-malate dicarboxylate shuttle or directly utilised for cytosolic nitrate reduction. Oxidation of succinate via cytochrome oxidase may also be similarly inhibited in light. Whether increase in the cytosolic ATP/ADP ratio in light is responsible for the inhibition of mitochondrial electron transfer to O2 is not clearly established, because the ATP/ADP ratio is reported to be already quite high in the dark. Effective collaboration between photophosphorylation and oxidative phosphorylation in order to maintain the cytosolic energy charge at a present high level is discussed. 相似文献
962.
Conservation of interphase chromatin nonhistone antigens as components of metaphase chromosomes 总被引:1,自引:0,他引:1
K W Adolph 《FEBS letters》1984,165(2):211-215
The degree of conservation of HeLa interphase chromatin nonhistone antigens among the nonhistones of isolated metaphase chromosomes was determined with immunological procedures. Proteins were separated on SDS-polyacrylamide gels and electrophoretically transferred to diazophenylthioether (DPT)-paper, which was then overlaid with antiserum to chromatin from interphase nuclei. The bound antibodies were detected with 125I-labeled protein A. Alternatively, polyacrylamide gels were directly overlaid with antiserum and with 125I-protein A. Densitometry of autoradiograms and stained gels revealed the degree of conservation of nonhistone antigenic determinants from interphase to metaphase to be over 90% for chromatin. 相似文献
963.
Sodium butyrate inhibits the synthesis of the transformation related protein p 53 in 3T6 mouse fibroblasts 总被引:3,自引:0,他引:3
Sodium butyrate, which blocks the cell cycle of many cell types in the G1 phase, strongly inhibits the synthesis of the transformation related, 53 kDa protein in 3T6 fibroblasts but much less so in SV 40 transformed mouse cells. By several criteria, this effect of the fatty acid appears to be indirect; p 53 synthesis takes place several hours after the butyrate-sensitive step in G1. The results are discussed in the light of a putative role of p 53 in growth control. 相似文献
964.
Summary Centrifugation of young seedlings ofTriticum durum andTriticum aestivum for 8–10 hours at 1,500–2,000 x g causes a serious disorder of the spatial organelle relationships in the interphase as well as the preprophase and mitotic subsidiary cell mother cells (SMCs). The nucleus, most organelles and cytoplasm are displaced to the centrifugal end of the cell, while the vacuoles lie at the other end. However, after centrifugation, the preprophase microtubule bands (PMBs) are nucleated and remain at the expected position close to the guard cell mother cells (GMCs). In some elongated SMCs the PMBs become completely separated from the nucleus. The mitotic spindle exhibits variable orientation and is usually formed at some distance from the PMB cortical zone.Cytokinesis in SMCs is spatially highly disturbed and the cell plate shows a variety of unpredictable dispositions, which seem to be determined by: 1. the position of the preprophase-prophase nucleus and the orientation of the mitotic spindle as well as their spatial relationships to the PMB cortical zone, and 2. the space available for cell plate growth. Many of the daughter cells exhibit a highly variable shape and size in different planes. Usually one edge of the cell plate partly or totally joins the anticlinal parent wall adjacent to the PMB cortical zone.In some SMCs ofZea mays andTriticum aestivum, the junction regions of the periclinal walls with the anticlinal ones, lined by the PMB cortical zone in normal SMCs, are detectably thickened after the arrest of mitosis and the prevention of interphase microtubule formation by a prolonged colchicine treatment. In a small number of protodermal cells of the same plants, participating in the development of stomatal complexes, irregular wall bodies or incomplete wall sheets were formed at wall regions lined by the PMB cortical zone.The presented observations are in line with the following hypotheses: 1. the PMB cortical zone interacts with the growing edges of the cell plate attracting it to fuse with the underlying parent wall when the latter approaches the former at a critical distance, and 2. in SMCs particular regions of the PMB cortical zone and/or the adjacent plasmalemma promote the local wall deposition in the absence of microtubules. 相似文献
965.
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
966.
Comparison between maize root cells and their respective regenerating protoplasts: wall polysaccharides 总被引:1,自引:0,他引:1
The cell-wall polysaccharides from different parts of maize roots have been analysed. The arabinose, galactose and mannose contents are influenced by cell differentiation, whereas xylose, rhamnose and uronic-acid contents are not. In cap cells, the pectin content is low but rhamnose and fucose are present in larger quantities. The cell-wall polysaccharides from cells of the elongation zone and their respective regenerating protoplasts were also analysed. The walls of the protoplasts contained higher xylose and mannose levels and a much lower level of cellulose than the cells from which they were derived. 相似文献
967.
Y. Kowyama T. Kawase H. Yamagata 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1984,68(4):297-303
Summary In order to examine changes in survival and mutation rates during a cell cycle in higher plant, fertilized egg cells of rice were irradiated with X-rays at 2 h intervals for the first 36 h after pollination, i.e., at different phases of the first and second cell cycles. The most sensitive phase in lethality was late G1 to early S, followed by late G2 to M, which were more sensitive than the other phases. In both M1 and M2 generations, sterile plants appeared most frequently when fertilized egg cells were irradiated at G2 and M phases. Different kinds of mutated characters gave rise to the respective maximum mutation rates at different phases of a cell cycle: namely, albino and viridis were efficiently induced at early G1, xantha at early S, short-culm mutant at mid G2, heading-date mutant at M to early G1. The present study suggests the possibility that the differential mutation spectrums concerning agronomic traits are obtained by selecting the time of irradiation after pollination. 相似文献
968.
Raymond D. Pratt John P. Johnson 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1984,805(4):405-411
Thyroid hormone (T3) has been demonstrated to inhibit the action of aldosterone on sodium transport in toad urinary bladder and rat kidney. We have exammined the effect of T3 on aldosterone action and specific nuclear binding in cultured epithelial cells derived from toad urinary bladder. In cell line TB6-C, addition of 5·10−8 M T3 to culture media for up to 3 days results in no change in short-circuit current or transepithelial resistance. This concentration of T3 completely inhibits the maximal increase in short-circuit current in response to 1·10−7 M aldosterone. The inhibition can be demonstrated with 18 h preincubation or with simultaneous addition of T3 and aldosterone. The half-maximal concentration for the inhibition of the aldosterone effect is approx. 5·10−9 M T3. T3 has no effect on cyclic AMP-stimulated short-circuit current in these cells. The effect of T3 on nuclear binding of [3H]aldosterone was examined using a filtration assay with data analysis by at least-squares curve-fitting program. Best fit was obtained with a model for two binding sites. The dissociation constants for the binding were K′d1 = (0.82 ± 0.36)·10−10 M and K′d2 = (3.2±0.60)·10−8 M.The half-maximal concentration for aldosterone-stimulated sodium transport in these cells is approx. 1·10−8 M. Analysis of nuclear aldosterone binding in cells preincubated for 18 h with 5·10−8 M T3 showed a K′d1 = (0.15 ± 0.10)·10−10 M and K′d2 = (3.5 ± 0.10)·10−8 M. We conclude that T3 i action of aldosterone on sodium transport at a site after receptor binding in the nucleus. 相似文献
969.
Jean Morisset 《Regulatory peptides》1984,10(1):11-22
The increases in DNA synthesis and total DNA content after caerulein treatment support the trophic effect of this CCK analog on the pancreas. Over a 15 day caerulein treatment, pancreatic growth plateaued after 5 days and somatostatin is believed to be responsible for this phenomenon. The present study was undertaken to test this possibility. Rats were treated for 2 or 4 days with caerulein (1 μg · kg?1), somatostatin antiserum plus caerulein or caerulein plus somatostatin (600 μg · kg?1). Caerulein increased all parameters studied after 2 and 4 days; pancreatic hyperplasia was established after 2 days. The somatostatin antiserum significantly enhanced the effect of caerulein, especially on DNA synthesis and contents after 2 and 4 days. The trophic effect of caerulein was significantly reduced by somatostatin dramatically so with respect to hyperplasia. The effects of the somatostatin antiserum and those of somatostatin on stimulated pancreatic growth support the hypothesis that somatostatin may be considered an endogenous growth inhibitory factor for the pancreas. 相似文献
970.
Summary Cell suspensions of Petunia hybrida were subjected to a selection procedure in which the concentration of the selective agent, methotrexate (MTX), was gradually elevated. In mammalian cells, this procedure frequently results in MTX-resistant mutants due to amplification of the gene coding for dihydrofolate reductase (DHFR), the target protein of MTX.Five suspension lines were isolated, with degrees of resistance ranging from 10 to 500 M MTX (in wild type the LD99.9 is 0.2 M). MTXR phenotypes were unstable, as manifested by the loss of resistance upon prolonged growth in the absence of drug. All of the mutants also exhibited high values of MTX-binding protein (60- to 400-fold higher than that of the wild type), which declined to intermediate values upon MTX withdrawal. Finally, cellular extracts from all of the mutants also showed high specific staining of DHFR-activity in gels.The results suggest that the resistance of MTX in these plant cell-lines is mediated by the elevation of the amounts of DHFR, probably as a consequence of gene amplification. 相似文献