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1.
Tansley Review No. 112 总被引:4,自引:0,他引:4
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The rogue tomato differs from the normal plant in that it exhibitsa lesser degree of apical dominance. Grafting techniques andmeasurements of the endogenous levels of growth substances inthe two types have been used in order to establish whether thisdifference is due to an altered hormonal balance in the roguetype. The results suggest that root-produced cytokinins play no rolein the control of apical dominance in the tomato plant, andthat lateral bud out-growth is influenced by a balance betweenapically-produced auxin, abscisic acid produced at the sitesof bud development and cytokinins synthesized within the budsthemselves. Lycopersicon esculentum L., tomato, apical dominance, abscisic acid, auxins, cytokinins, growth regulation 相似文献
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Summary. Blood samples from a female sheep-goat hybrid and its back-cross male offspring were tested for electrophoretic variants of plasma albumin, transferrin and esterase, and of red cell carbonic anhydrase, nucleoside phosphorylase, NADH-diaphorase, 'X'-protein, superoxide dismutase, malic enzyme and haemoglobin. Red cells were also tested for blood group antigens. Both animals showed variants that could not be attributed to either sheep or goat alone, thus confirming previous chromosomal data that the female was a genuine sheep-goat hybrid. 相似文献
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Carbonic Anhydrase and the Regulation of Photosynthesis 总被引:14,自引:0,他引:14
THE role of CO2 in the regulation of photosynthetic and respiratory metabolism in plants is little understood in the unicellular alga Chlorella pyrenoidosa; for example, after autotrophic growth in high CO2 (5·5% by volume), transfer to a CO2 concentration about ten times less than the concentration in air results initially in low rates of photosynthesis characterized by the virtual absence of the Calvin cycle1 of CO2 fixation2. An induction period of about 2 h is necessary before normal photosynthetic rates are established. Cells grown in air (0.03% CO2) do not show this effect and photosynthesize at comparatively high rates even in very low concentrations of CO2. 相似文献
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Compared to air-breathers, animals that respire aquaticallyhave limited access to O2 and their habitats are more subjectto hypoxia. Because O2 diffuses more slowly through water thanair, animals in water experience greater diffusion boundarylayer effects on respiratory gas diffusion. While ventilationand specialized exchange surfaces mitigate O2 diffusion limitationson respiration, most animal phyla, particularly those confinedto aquatic habitats, lack these. Diffusion limitation influencesthe ontogeny of aquatic animals and may have also shaped Precambrianmetazoans. In spite of a more limited O2 access, aquatic animalsdisplay a much greater spectrum of respiratory adaptation, rangingfrom the loss of Hb in icefishes to the independent evolution,invention, and acquisition of Hb in many invertebrates confinedto hypoxic habitats. Three features of aquatic respiratory systemsdistinguishing them from aerial systems are the widespread occurrenceof integumental respiration, the frequent presence of combinedrespiratory and feeding surfaces, and the profound effect ofhypoxia on shaping respiratory adaptation, both in shallow waterand in the deep sea. 相似文献
7.
Axenic Cultivation of Entamoeba dispar Brumpt 1925, Entamoeba insolita Geiman and Wichterman 1937 and Entamoeba ranarum Grassi 1879 总被引:2,自引:0,他引:2
C. GRAHAM CLARK 《The Journal of eukaryotic microbiology》1995,42(5):590-593
ABSTRACT. Three species of Entamoeba have been grown in axenic culture for the first time. In two cases, novel methods for adapting the organisms to growth without bacteria were employed. While E. ranarum was axenized by the classic technique of Diamond, from a monoxenic culture with Trypanosoma cruzi as the associate, both E. dispar and E. insolita were first grown in axenic culture medium supplemented with lethally irradiated bacteria. From there, E. insolita was axenized directly, but E. dispar initially required the presence of fixed bacteria. After prolonged culture under this technically axenic but unwieldy culture system, E. dispar was eventually adapted to growth in the absence of added bacteria. 相似文献
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TUCKER WB 《Public Health Reports》1958,73(10):950-955
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Drought and Oxidative Load in the Leaves of C3 Plants: a Predominant Role for Photorespiration? 总被引:10,自引:0,他引:10
NOCTOR GRAHAM; VELJOVIC-JOVANOVIC SONJA; DRISCOLL SIMON; NOVITSKAYA LARISSA; FOYER CHRISTINE H. 《Annals of botany》2002,89(7):841-850
Although active oxygen species are produced at high rates inboth the chloroplasts and peroxisomes of the leaves of C3 plants,most attention has focused on the potentially damaging consequencesof enhanced chloroplastic production in stress conditions suchas drought. This article attempts to provide quantitative estimatesof the relative contributions of the chloroplast electron transportchain and the glycolate oxidase reaction to the oxidative loadplaced on the photosynthetic leaf cell. Rates of photorespiratoryH2O2 production were obtained from photosynthetic and photorespiratoryflux rates, derived from steady-state leaf gas exchange measurementsat varying irradiance and ambient CO2. Assuming a 10 % allocationof photosynthetic electron flow to the Mehler reaction, photorespiratoryH2O2 production would account for about 70 % of total H2O2 formedat all irradiances measured. When chloroplastic CO2 concentrationrates are decreased, photorespiration becomes even more predominantin H2O2 generation. At the increased flux through photorespirationobserved at lower ambient CO2, the Mehler reaction would haveto account for more than 35 % of the total photosynthetic electronflow in order to match the rate of peroxisomal H2O2 production.The potential signalling role of H2O2 produced in the peroxisomesis emphasized, and it is demonstrated that photorespiratoryH2O2 can perturb the redox states of leaf antioxidant pools.We discuss the interactions between oxidants, antioxidants andredox changes leading to modified gene expression, particularlyin relation to drought, and call attention to the potentialsignificance of photorespiratory H2O2 in signalling and acclimation. 相似文献