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991.
Photosynthesis, photorespiration and nitrogen metabolism 总被引:16,自引:6,他引:10
ROGER M. WALLSGROVE ALFRED J. KEYS PETER J. LEA BENJAMIN J. MIFLIN 《Plant, cell & environment》1983,6(4):301-309
Abstract. The ATP and reduced ferredoxin generated in photosynthetic reactions in the chloroplast are utilized for a large number of reactions other than CO2 -fixation. Quantitatively the most important reaction is the reassimilation of ammonia liberated during photorespiration in C3 plants via the glutamate synthase cycle. Chloroplasts are also able to reduce nitrite to ammonia, sulphate to sulphide, and synthesize a number of amino acids. The amino acids essential for human nutrition are all synthesized in the chloroplast and evidence is presented to suggest that they may be the sole site of such biosynthetic reactions. 相似文献
992.
SYNOPSIS. Uptake of 14C-labeled alanine, glutamate, lysine, methionine, proline, and phenylalanine by Trypanosoma equiperdum during 2-minute incubations occurred by diffusion and membrane-mediated processes. Amino acid metabolism was not detected by paper chromatography of trypanosome extracts. Most of 18 carbohydrates tested for ability to alter amino acid transport neither changed nor significantly inhibited transport. Glucose, however, stimulated glutamate, lysine and proline transport; fructose stimulated lysine uptake and 2-deoxy-D-glucose increased phenylalanine and methionine absorption. No evidence was found that the carbohydrates acted by binding to amino acid transport “sites.” Glucose inhibition of alanine, phenylalanine, and methionine uptake was linked to glycolysis. The rapid formation of alanine from glucose stimulated alanine release and, when glycolysis was blocked, glucose no longer inhibited alanine transport. Methionine and phenylalanine release was also stimulated by glucose. Glucose changed the ability of lysine, glutamate, and proline to inhibit each others’uptake, indicating that certain amino acids are preferentially absorbed by respiring cells. Analysis of free pool amino acid levels suggested that some amino acid transport systems in T. equiperdum are linked in such a way to glycolysis as to control the cell concentrations of these amino acids. 相似文献
993.
Tails of Tetrahymena 总被引:6,自引:0,他引:6
SYNOPSIS. The source of force generation of beating cilia and flagella is an interaction between the doublet microtubules mediated by the dynein-1 arms which cause the doublets to slide relative to one another. Previously, we demonstrated direct sliding of Tetrahymena ciliary axonemes by dark field light microscopy. In this paper, the results of such an experiment have been captured on a polylysine-coated grid surface for whole-mount electron microscopy. Images in which sliding between doublets has taken place can be identified. We conclude that doublets slide relative to one another with a constant polarity. To produce the observed displacement, the direction of the dynein-1 arm force generation must be from base to tip, so that the doublet (n), to which the arms are attached, pushes the next doublet (n+ 1) toward the tip. In addition to the functional polarity, the dynein-1 arms are found to have a structural polarity: they tilt toward the base when viewed along the edges of the A-subfiber. A scheme is presented which reconciles the finding of a single polarity of active sliding with the geometry of microtubule tip displacement of bent cilia. 相似文献
994.
Aspects of Scotia Sea zooplankton 总被引:2,自引:0,他引:2
INI GO EVERSON PETER WARD 《Biological journal of the Linnean Society. Linnean Society of London》1980,14(1):93-101
Information on small scale distributions of three species of Antarctic zooplankton is reviewed. Aggregations of the euphausiid Euphausia superba , the tunicate Salpa thompsoni , and the amphipod Parathemisto gaudichaudii are compared, and the manner in which such aggregations mav arise is discussed. A possible relationship between swarming and feeding activity in E. superba is suggested in which krill are thought to be dispersed whilst feeding but that on repletion they swarm. It is thought that this may account for this species' irregular spatial distribution as recorded bv previous expeditions. A further consequence of this theory is that during the Winter swarming will be minimal. 相似文献
995.
Solid state photosensors with their many advantages have not been utilized for chlorophyll fluorescence research. One reason is their reputed low photosensitivity compared to photomultiplier tubes. A photodarlington sensor has a relatively low photosensitivity and a nonlinear current output versus light intensity. However, when incorporated into an apparatus described in this paper it can respond to fluorescence signals from leaves using light excitation as low as 500 μW/cm2. The sensitivity of another solid state device (photovoltaic photodiode) was compared to five photomultipliers using a monochromator-microphotometer testing apparatus. This solid state sensor proved to have equal or greater sensitivity to chlorophyll fluorescence. An apparatus incorporating the photovoltaic photodiode is discussed. 相似文献
996.
997.
Temperature exposures which normally decrease growth of Pisum sativum seedlings by 50 % were found to be lethal in plants whose cotyledons were removed. Utilization of the two major reserves, starch and protein, decreased at high temperatures. However, the two enzymes responsible for their hydrolysis were thermostable. It appears that the influence of high temperatures on seedling growth is not due to direct effects of temperature on cotyledon metabolism, but rather indirectly through the axis. 相似文献
998.
SYNOPSIS. Biochemical adaptation to environmental parameterssuch as temperature appears to involve two distinct types ofchanges in the organism's chemistry. On the one hand, the quantitiesof certain molecular species present in the cells may change.Alternatively, the actual types of molecules present may vary.Rainbow trout (Salmo gairdneri) acclimated to warm and coldtemperatures exhibit a striking example of this latter typeof adaptation. For all enzymes we have examined in this species,distinct "warm" and "cold" isozymes are present. The isozymesfound in warmacclimated (18°C) trout function well onlyat temperatures above 1012°C. The isozymes presentin cold-acclimated (4°C) trout function optimally at 2-5°C,temperatures this species normally encounters in winter. Thesedata, plus information on comparable changes in membrane lipids,lead us to propose that adult poikilotherms may undergo a considerabledegree of "biochemical restructuring" on a seasonal basis. Thefactors which control this "restructuring," and the rates atwhich the process occurs at high and low temperatures, are topicsfor future investigation. 相似文献
999.
Regulation of Growth in Avena (Oat) Stem Segments by Gibberellic Acid and Abscisic Acid 总被引:1,自引:0,他引:1
The purpose of this study was to analyze the nature of the interaction between gibberellic acid (GA3) and abscisic acid (ABA) in the regulation of growth in excised Avena (oat) stem segments. Growth, compared to sucrose controls, was inhibited by ABA in the range of 10?4 to 10?6M. GA3-promoted growth was also inhibited by ABA in the same concentration range. A Lineweaver-Burk analysis of the interaction between GA3 and ABA indicated that ABA acts in a non-competitive fashion with GA3. This same result was obtained previously with GA3-indoleacetic acid (IAA) and GA3-kinetin interactions with Avena stem sections. Our results indicate that ABA can inhibit GA3-promoted growth within physiological concentrations, and that it is probably acting at a different physiological site from that for GA3. 相似文献
1000.
SPECIFIC immunoreactivity can be conferred on lymphoid cells by incubation with RNA-rich extracts prepared from lymphoid tissues exposed to specific antigens in vivo1 and in vitro2,3. We have shown transfer of immunity to tumour specific antigens in vivo4 and in vitro5 by incubation of syngeneic spleen cells in vitro with RNA extracted from the lymphoid tissues of xenogeneic or syngeneic animals immunized with the tumour to be treated. Administration of these spleen cells to normal animals decreased the development and growth of isografts of the same tumour. 相似文献