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Indirect evidence suggests that legumes can adjust rapidly theresistance of their root nodules to O2 diffusion. Here we describeexperiments using O2 specific micro-electrodes and dark fieldmicroscopy to study directly the operation of this diffusionbarrier. The O2 concentration sensed by the electrode decreasedsharply in the region of the inner cortex and was less than1.0 mmol m3 throughout the infected tissue in nodulesof both pea (Pisum sativum) and french bean (Phaseolus vulgaris).In a number of experiments the ambient O2 concentration wasincreased to 40% while the electrode tip was just inside theinner cortex. In 13 out of 21 cases the O2 concentration atthis position either remained low and unchanged or increasedirreversibly to near ambient values. In the remaining casesthe O2 concentration increased after 1 to 2.5 min and then decreasedto its former value. These results are ascribed to an increasein resistance of the barrier in response to increased O2 fluxinto the nodule. It was shown microscopically that air spacesboth at the boundary between the infected zone and the innercortex, and within the infected zone started to disappear 3min after nodules were exposed to high ambient O2 concentrationsand had disappeared completely after 8 min. These spaces werenot changed by exposure of the nodule for 10 min to either N2or air. Key words: Oxygen, root nodules, air spaces 相似文献
3.
Evolution of the 28S ribosomal RNA gene in anurans: regions of variability and their phylogenetic implications 总被引:1,自引:0,他引:1
Fifteen restriction sites were mapped to the 28S ribosomal RNA gene of
individuals representing 54 species of frogs, two species of salamanders, a
caecilian, and a lungfish. Eight of these sites were present in all species
examined, and two were found in all but one species. Alignment of these
conserved restriction sites revealed, among anuran 28S rRNA genes, five
regions of major length variation that correspond to four of 12 previously
identified divergent domains of this gene. One of the divergent domains
(DD8) consists of two regions of length variation separated by a short
segment that is conserved at least throughout tetrapods. Most of the
insertions, deletions, and restriction-site variations identified in the
28S gene will require sequence-level analysis for a detailed reconstruction
of their history. However, an insertion in DD9 that is coextensive with
frogs in the suborder Neobatrachia, a BstEII site that is limited to
representatives of two leptodactylid subfamilies, and a deletion in DD10
that is found only in three ranoid genera are probably synapomorphies.
相似文献
4.
ATP:AMP phosphotransferase (EC 2.7.4.3) (adenylate kinase) has been purified 1746-fold from Mycobacterium marinum (ATCC 927) by successive column chromatography on DEAE-cellulose (DE-53), Reactive Blue agarose, Sephadex G-75, hydroxyapatite and, finally, DEAE-Sephadex A-50. The final enzyme preparation had a specific activity of 576 mumol/min per mg protein with an overall yield of 51%. The preparation was homogeneous by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The enzyme was estimated to have an Mr of 29500 and an isoelectric point of 6.7, properties which generally resemble those of the mitochondrial enzyme. Indeed, the two enzymes failed to separate when subjected to polyacrylamide gel electrophoresis under denaturing conditions. The extinction coefficient (at 276 nm) was calculated to be 3.114 X 10(4) M-1 X cm-1 and E1%1cm = 10.556. Adenylate kinase was present at a concentration of 0.06 mg/g (wet weight) bacteria. Enzyme was stable for months in 60% glycerol in the freezer; at 4 degrees C, less than 5% of the activity was lost over a 7 day period. 相似文献
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Batra , Lekh R., and Richard P. Korf . (Cornell U., Ithaca, N. Y.) The species of Ciborinia pathogenic to herbaceous angiosperms. Amer. Jour. Bot. 46(6): 441–450. Illus. 1959.—On the basis of anatomical studies, 2 distinct species of Ciborinia, a generic segregate of Sclerotinia, are shown to occur on Erythronium. The life history and phytopathology of one of these, C. erythronii, are reported. The species is shown to be homothallic, to develop its sclerotia in nearly all parts of the plant, to overwinter also in the form of mycelium in bulbs, and to form spermatia in the field. Experiments on factors affecting formation of sclerotia and apothecia in the laboratory are reported. Prolonged washing of sclerotia formed in the laboratory proved to be an important factor for development of apothecia. A new species, C. trillii, pathogenic to Trillium is described, as is a new species, C. violae, pathogenic to Viola. The generic diagnosis of Ciborinia is emended on the basis of these studies. A new combination, C. hirtella, is also proposed. 相似文献