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941.
Data from measurements of optical density of intact tissue and of anthocyanins in extracts resolved on cellulose thin layer plates were compared with visual evaluations of color quality and intensity in poinsettia, rose, and snapdragon. Visual evaluation was in good agreement with both instrumental and chemical determinations. However, the number or kinds of anthocyanins present could not be predicted from the visual evaluation or from the spectra of the fresh tissue. Data from the resolved extracts did not provide a basis for predicting the optical-density spectrum or the color of the intact tissue. In addition to the genetic factors which have been shown to control (1) the type of anthocyanin, (2) the amount of anthocyanin, and (3) the distribution of anthocyanins within the flower, we suggest another group of genes which apparently affect color through control of structural modification of individual anthocyanins in the living cell through shift in pH, metal chelation, and/or copigmentation. Such genes are apparently responsible for the modification of red color within the Wh Wh genotype of poinsettias containing both pelargonidin and cyanidin glycosides and for a very similar pink color in a snapdragon and a rose, each containing a single anthocyanin, a pelargonidin glycoside, and a cyanidin glycoside, respectively. 相似文献
942.
Light-Induced Changes in the Fluorescence Yield of Chlorophyll a In Vivo: IV. The Effect of Preillumination on the Fluorescence Transient of Chlorella pyrenoidosa 下载免费PDF全文
The fluorescence transient of Chlorella pyrenoidosa, excited by saturating blue light, has a base level O, hump I, dip D, peak P, and at 1.5 sec a quasi-steady level S (12). With 2 sec exciting exposures and 4 min dark periods, preillumination-1 (lambda >/= 690 nm, intensities 1-750 ergs/sec-cm(2) incident), replacing the dark periods, lowers I more effectively than preillumination-2 (650 nm = lambda = 680 nm) in both aerobic and anaerobic cells. Results indicate that the intersystem electron transport pool A as well as the primary electron acceptor of pigment system II Q (fluorescence quencher) is normally being reduced at I. Preillumination-1 lowers and delays P. Preillumination-2 (absorbed by both pigment systems) also lowers P, but delays P only at low intensity; at high intensity it hastens P. Preillumination-1 raises S while preillumination-2 lowers S. With 30 instead of 2 sec exciting light exposures, preillumination-1 causes a large S increase, and at low intensity a P increase. The S effects seem to be of a long-term nature (26-29) rather than rapid changes in the redox state of Q. As exciting light intensity increases, fluorescence yield at P increases three-fold maximally. The ratio of P (anaerobic) to O (aerobic) is 5.5. These high ratios restrict the Franck-Rosenberg model of photosynthesis (13), which is based on fluorescence yield doubling. 相似文献
943.
FLAGELLAR ELONGATION AND SHORTENING IN CHLAMYDOMONAS : The Use of Cycloheximide and Colchicine to Study the Synthesis and Assembly of Flagellar Proteins 总被引:81,自引:56,他引:25 下载免费PDF全文
Flagella can be removed from the biflagellate Chlamydomonas and the cells begin to regenerate flagella almost immediately by deceleratory kinetics. Under usual conditions of deflagellation, more than 98% of all flagella are removed. Under less drastic conditions, cells can be selected in which one flagellum is removed and the other left intact. When only one of the two flagella is amputated, the intact flagellum shortens by linear kinetics while the amputated one regenerates. The two flagella attain an equal intermediate length and then approach their initial length at the same rate. A concentration of cycloheximide which inhibits protein synthesis permits less than one-third of each flagellum to form when both flagella are amputated. When only one is amputated in cycloheximide, shortening proceeds normally and the degree of elongation in the amputated flagellum is greater than if both were amputated in the presence of cycloheximide. The shortening process is therefore independent of protein synthesis, and the protein from the shortening flagellum probably enters the pool of precursors available for flagellar formation. Partial regeneration of flagella occurs in concentrations of cycloheximide inhibitory to protein synthesis suggesting that some flagellar precursors are present. Cycloheximide and flagellar pulse-labeling studies indicate that precursor is used during the first part of elongation, is resynthesized at mid-elongation, and approaches its original level as the flagella reach their initial length. Colchicine completely blocks regeneration without affecting protein synthesis, and extended exposure of deflagellated cells to colchicine increases the amount of flagellar growth upon transfer to cycloheximide. When colchicine is applied to cells with only one flagellum removed, shortening continues normally but regeneration is blocked. Therefore, colchicine can be used to separate the processes of shortening and elongation. Radioautographic studies of the growth zone of Chlamydomonas flagella corroborate previous findings that assembly is occurring at the distal end (tip growth) of the organelle. 相似文献
944.
945.
John F. Thomson Duane A. Habeck Sharron L. Nance Karen L. Beetham 《The Journal of cell biology》1969,41(1):312-334
During the first 3 days of exposure of rats to 5°C, the nitrogen concentration of interscapular brown fat increased by 50% and remained at this elevated level for the duration of the 8-wk observation period, while the mass of tissue increased fourfold. The concentration of both DNA and RNA per unit nitrogen reached a maximum after 3 days, then declined; however, the total quantity of each continued to rise. The concentration of various respiratory enzymes decreased during the first few days and then increased, but at different rates. The morphological changes in mature brown fat cells during cold acclimation were observed to be: a reduction in fat droplet size during the first 3 days, followed by a gradual increase in size through 6 wk in the cold; a continual increase in the amount of intermitochondrial ground substance during the first 3 wk, with increased granularity and glycogen content after 1 wk; initial disappearance of glycogen between mitochondria, followed by the reappearance of a few isolated particles in the intermitochondrial ground substance after 1 wk in the cold; initial increase in the density of intramitochondrial matrix for the first 3–4 days, followed by a gradual return to the control density; loss in integrity of mitochondrial outer membranes during the first 4 days, followed by gradual but incomplete restoration; temporary loss of the dense material in lipid droplets during the first 24 hr, with return after 1 wk in the cold; and a 40% increase in mitochondrial diameter within 1 day, followed by a decrease in diameter within 1 wk to a constant value about 15% larger than the controls. 相似文献
946.
Electron Microscopic Observations on the Ribonucleic Acid of Murine Leukemia Virus 总被引:12,自引:9,他引:3 下载免费PDF全文
The ribonucleic acid (RNA) of murine leukemia virus (MLV) Rauscher strain was observed by the aid of electron microscopy with the use of the protein monolayer technique. RNA was observed directly after release from virus particles or after isolation by sedimentation in sucrose density gradients. Molecules were found in an extended linear form. Many of the RNA filaments released by detergent treatment contained curled regions, suggesting the linear filaments were originally coiled within the virus particle. The relationship of the curled areas to the containment of the RNA within the virus particle is discussed, and a mechanism for the inclusion of RNA in the budding virion is proposed. Treatment of the extended MLV-RNA with dimethyl sulfoxide resulted in the collapse of the molecule forming a tangled complex. Treatment with urea or heating at 50 C in 3 mm NaCl also produced this effect. Also under the conditions in which MLV-RNA was linear, RNA from Rous sarcoma virus also was linear, but Newcastle disease virus RNA and ribosomal RNA of rat liver had collapsed structures. The results indicated that the RNA of MLV, and perhaps other RNA-containing tumor viruses, has a specific unique conformation dependent upon hydrogen bonds. 相似文献
947.
Chilling injury and changes in adenosine triphosphate of cotton seedlings 总被引:15,自引:11,他引:4 下载免费PDF全文
Young Gossypium hirsutum L. seedlings chilled at 5° showed a continual decrease in ATP concentration with time of chilling. Chilled plants returned to optimum conditions were able to restore the initial ATP concentration when chilled only 1 day, but not when chilled 2 days. The decrease in ATP with chilling was prevented by hardening the seedlings at 15° for 2 days (14-hr-day-length) immediately before chilling. The ATP level of hardened plants was higher than of unhardened plants. When hardened plants were chilled at 5°, the ATP level increased in the leaves but decreased in the roots. 相似文献
948.
Urea metabolism was studied with nitrogen-starved cells of Chlorella vulgaris Beijerinck var. viridis (Chodat), a green alga which apparently lacks urease. Incorporation of radioactivity from urea-(14)C into the alcohol-soluble fraction was virtually eliminated in cell suspensions flushed with 10% CO(2) in air. This same result was obtained when expected acceptors of urea carbon were replenished by adding ornithine and glucose with the urea. Several carbamyl compounds, which might be early products of urea metabolism and a source of the (14)CO(2), were not appreciably labeled. If cells were treated with cyanide at a concentration which inhibited ammonia uptake completely and urea uptake only slightly, more than half of the urea nitrogen taken up was found in the medium as ammonia. Cells under nitrogen gas in the dark were unable to take up urea or ammonia, but the normal rate of uptake was resumed in light. Since 3-(3,4-dichlorophenyl)-1,1-dimethylurea did not selectively inhibit this uptake, an active respiration supported by light-dependent oxygen evolution in these cells was ruled out. A tentative scheme for urea metabolism is proposed to consist of an initial energy-dependent splitting of urea into carbon dioxide and ammonia. This reaction in Chlorella is thought to differ from a typical urease-catalyzed reaction by the apparent requirement of a high energy compound, possibly adenosine triphosphate. 相似文献
949.
Summary Observations on the inhibition of root elongation and cell division in Allium cepa showed that the toxic effects of scandium and aluminium were very similar. Tracer uptake studies using 46Sc indicated that the rate of uptake in the apical 3.0 mm of the axis was more rapid than elsewhere in the root and proceeded in two distinct phases; Phase 1, probably superficial adsorption, was characterised by a rapid initial rate which was little affected by low temperature, the rate of Phase 2 was slower but remained constant for 24 hours and was highly dependent on temperature.Autoradiographs from roots treated for 30 min with 46Sc showed that most of the isotope in the root tip was concentrated in a peripheral belt corresponding with the mucigel layer of the root cap and it is suggested that this is the site of Phase 1 adsorption. The underlying root cap and epidermal cells retained little scandium but interior to them some isotope was associated with dividing cells; this increased steadily over 6 hour to an estimated concentration of 30 mM, and possibly represents Phase 2 uptake. Differentiation and secondary wall formation in the cortex restricted the rate of radial penetration of scandium. The primary endodermis restricted the entry of scandium into the stele at a very early stage in its development, which leads to the conclusion that migration of the ion across the root is primarily in the free space.Scandium enters the dividing cells in advance of observable effects on cell division, a situation compatible with the direct involvement of this ion in the inhibition of the mitotic cycle. Suggestions are made on the mechanisms by which polyvalent cations might disturb cell division and extension. 相似文献
950.
John Mackay-Dick 《BMJ (Clinical research ed.)》1969,1(5639):316-317