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71.
John Kuo 《American journal of botany》1983,70(2):159-164
The nacreous walls of sieve elements occur in seagrasses in all three genera of the family Zosteraceae and the genus Halodule of the family Cymodoceaceae but are absent from another eight seagrass genera belonging to the families Hydrocharitaceae, Cymodoceaceae, and Posidoniaceae. They occur in leaf blades, leaf sheaths, rhizomes, and erect stems but are not present in root tissues. The nacreous wall is uneven along the inner limits reflecting irregular thickness. The wall consists of hemicellulose or pectin and cellulose, but no protein, lignin, or lipid. Ultrastructurally, the wall contains parallel microfibrils or loose fibrils embedded in an amorphous matrix. Open pores occur in sieve plates and branching plasmodesmata are present in enlarged sieve areas. Mitochondria, endoplasmic reticulum, and plastids are also present in these sieve elements. 相似文献
72.
Demonstration of an “Excitation-Contraction Recoupling” Mechanism in Mammalian Ventricular Myocardium 总被引:1,自引:0,他引:1
A PROCESS called “excitation-contraction coupling” has been generally accepted to take place only in the direction of excitation to contraction. Through this mechanism a propagated action potential initiates an active state in skeletal or cardiac muscle and the muscle contracts. We propose that, in the mammalian ventricular myocardium at least, the process is not unidirectional and an important reverse coupling between the contractile system and the excitable plasma membrane has been overlooked. Through this feedback interaction the mode of contraction (that is, isotonic or isometric) not only determines the instantaneous electrical state of the plasma membrane, but also influences the mechanical events of the subsequent beats. Thus when Kaufmann et al.1 recorded intracellular action potentials from cat papillary muscle, the time course of the repolarization was altered depending on the mode of contraction. Some kind of contraction-excitation feedback has also been suggested by Stauch2 and Lab3,4. They showed a difference in the shape of the monophasic action potential, as recorded by a suction electrode, when comparing isotonic and isovolumic contraction of the intact ventricle. But their experimental conditions did not allow satisfactory analysis of the phenomenon. 相似文献
73.
74.
Function of the <Emphasis Type="Italic">rel</Emphasis> Gene in <Emphasis Type="Italic">Escherichia coli</Emphasis> 总被引:6,自引:0,他引:6
Sokawa et al. suggest that rel- strains of Escherichia coli possess abnormal protein synthesizing machinery, which cannot carry out normal protein synthesis when the supply of amino-acids is limited. 相似文献
75.
AVRAM HERSHKO PIERRE MAMONT ROBERT SHIELDS GORDON M. TOMKINS 《Nature: New biology》1971,232(33):206-211
A hypothesis has been developed to relate stringent control in bacteria to a set of interactions involved in the regulation of growth of transformed and untransformed mammalian cells. 相似文献
76.
Kimball and Wilson1 reported that the arabinose analogue of cytidine (ara-C) inhibited DNA polymerase in a crude extract prepared from Ehrlich ascites cells. Furth and Cohen2 observed cytosine arabinoside triphosphate (ara-CTP) inhibited DNA polymerase in extracts from either calf thymus or bovine lymphosarcoma tissue, although these investigators3 had already found no effect of ara-CTP on DNA polymerase from Escherichia coli. The inhibition in both of these cases could be substantially reversed by dCTP; but incorporation of the arabinose nucleotide (ara-CMP) into DNA could not be unequivocally demonstrated. Graham and Whitmore4 reported the incorporation of ara-C into DNA in vivo and the inhibition of a DNA polymerase from L cells by ara-CTP. They found that ara-CMP was initially incorporated into small DNA strands but subsequently appeared in long strands. Momparler5 has presented evidence that, in vitro, ara-C incorporation was limited to the 3′-hydroxyl end of DNA chains. Such incorporation might be expected to block further chain elongation but this expectation was not supported by the evidence presented by Graham and Whitmore. 相似文献
77.
ALINA TAYLOR 《Nature: New biology》1971,234(48):144-145
JACOB and Fuerst1,2 demonstrated the presence of a bacteriolytic enzyme (λ-endolysin) in the induced cultures of lysogenic Escherichia coli K12 (λ). The enzyme was later identified as the product of gene R; of phage λ3 which is involved in bacterial lysis at the end of a latent period. The enzyme is apt to form spheroplast-like structures in E. coli2 and one would therefore expect its substrate to be murein. 相似文献
78.
S H Chang S Kuo E Hawkins N R Miller 《Biochemical and biophysical research communications》1973,51(4):951-955
The nucleotide sequence of “Renaturable” leucine transfer RNA from Baker's yeast has been re-investigated. The results showed that (i) this tRNA has a sequence of DCD at positions 19–21, (ii) it has an anticodon m5CAA and (iii) it has a pseudouridine at position 40. 相似文献
79.
80.
Isolation of amylolytic strains of Thermoactinomyces vulgaris and production of thermophilic actinomycete amylases 总被引:6,自引:1,他引:5
Kuo, M. J. (Iowa State University, Ames), and P. A. Hartman. Isolation of amylolytic strains of Thermoactinomyces vulgaris and production of thermophilic actinomycete amylases. J. Bacteriol. 92:723-726. 1966.-Of 759 isolates obtained from dung, compost, and soil samples, a culture of Thermoactinomyces vulgaris (strain 5) was selected for further study on the basis of quantities of amylase produced in synthetic and nonsynthetic media, rapid growth and sporulation, culture stability upon prolonged storage at 5 C, and growth temperature range. Inoculum preparation, temperature optimum for amylase formation, and the effects of various kinds and levels of carbon and nitrogen sources on amylase production were studied with T. vulgaris strain 5. An optimal procedure for production of T. vulgaris amylases is proposed. 相似文献