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581.
582.
R D Britt G A Lorigan K Sauer M P Klein J L Zimmermann 《Biochimica et biophysica acta》1992,1140(1):95-101
The amplitude of the g = 2 Mn 'multiline' EPR signal of the S2 state of the photosynthetic oxygen-evolving complex varies inversely with temperature, indicating that this signal arises from a ground spin state. Electron spin echo experiments at temperatures of 4.2 K and 1.4 K show such Curie-law behavior of the g = 2 multiline EPR signal, as do continuous-wave EPR experiments performed at a non-saturating microwave power in the range from 15.0 K to 4.2 K. 相似文献
583.
584.
Lycopodium annotinum, a clonal pteridophyte, was grown under canopies formed by various combinations of deciduousVaccinium myrtillus and evergreenV. vitis-idaea. The canopies differed in red:far-red ratio, withV. myrtillus giving the lowest ratio. The current year's horizontal segments ofL. annotinum had the same specific weight in all treatments, but the lengths of the segments were significantly increased when grown under the canopy ofV. myrtillus compared withV. vitis-idaea. The number of vertical apices was also increased. Both these responses increased the amount of assimilating structures ofL. annotinum when growing under aV. myrtillus canopy. This might be beneficial for the evergreenL. annotinum, since it can then utilize spring and autumn periods when the deciduousV. myrtillus has no leaves. 相似文献
585.
Janice P. Lea Daryl O. Crenshaw Stephen J. Onufrak Britt B. Newsome William M. McClellan 《Obesity (Silver Spring, Md.)》2009,17(12):2216-2222
Obesity is highly prevalent in African Americans and is associated with increased risk of End‐Stage Renal Disease (ESRD) and death. It is not known if the effect of obesity is similar among blacks and whites. The aim of this study is to examine racial differences in the association of obesity with ESRD and survival in elderly patients (age >65). Data were obtained for 74,167 Medicare patients with acute myocardial infarction (AMI) between February 1994 and July 1995. BMI was calculated as weight (kg) divided by height (m2). We evaluated the association of BMI class with ESRD incidence and death using multivariable Cox proportional hazards models, testing for race‐BMI interactions. Compared to whites, African Americans had higher BMI (26.9 vs. 26.0, P < 0.0001) and estimated glomerular filtration rate (72.4 ml/min/1.73 m2 vs. 66.6 ml/min/1.73 m2, P < 0.0001). Crude ESRD rates increased with increasing obesity among whites but not among blacks. However, after adjusting for age, sex, and other comorbidities, obesity was not associated with increased ESRD rate among blacks or whites and the interaction between race and BMI was not significant. Furthermore, for both races, patients classified as overweight, class 1 obese, or class 2 obese had similar, significantly better survival abilities compared to normal weight patients and the race BMI interaction was not significant. In conclusion, obesity does not increase risk of ESRD among black or white elderly subjects with cardiovascular disease (CVD). However, both obese blacks and whites, in this population, experience a survival benefit. Further studies need to explore this obesity paradox. 相似文献
586.
During embryogenesis in insects, the axonscaffold of the brain is built around the embryonic foregut which separates the
anlagen of the brain hemispheres. Here, we investigate this process in Drosophila and show that the major longitudinal and horizontal tracts of the embryonic brain form superficially near the interface between
the foregut and embryonic brain hemispheres. We identify three types of cellular structures which might be involved in tract
formation. These are rows of glial cells at the medial brain margin, cellular bridges composed of neuronal somata and the
epithelial surface of the foregut itself. The close proximity to the outgrowing axons suggests that the structures at the
brain-foregut interface may play a role in the morphogenesis of embryonic brain tracts in Drosophila.
Received: 11 November 1996 / Accepted: 3 January 1997 相似文献
587.
588.
A coverslip culture technique for the growth of fungi, with subsequent preparation of permanent mounts for microscopic examination, is described. This simplified technique allows examination at different stages of development of the fungus, or can be used in the preparation of large numbers of similar mounts for teaching purposes. 相似文献
589.
Abstract The effects of heat shock upon the expression of several developmentally regulated genes of Myxococcus xanthus were examined. No effects were observed on levels or timing of developmentally regulated β-galactosidase expression in eight randomly selected Tn5lac insertion mutants. However, heat shock significantly affected the fruiting behavior of temperature-sensitive aggregation ( tag ) mutants of M. xanthus . The tag mutant phenotype exhibits the normal aggregation of cells to form fruiting bodies at temperatures < 34°C, but cells fail to aggregate at temperatures ⩾ 34°C. Heat shock administered to tag mutant strains prior to starvation prohibited fruiting body formation at permissive temperatures. Additionally, tag mutant strains were found to be extremely sensitive to killing at 40°C. Heat shock was also found to increase tagA and tagE expression by 22 and 47%, respectively. Mutations in tagA blocked heat shock induced expression of tagE . 相似文献
590.
David B. Goodin Vittal K. Yachandra R. David Britt Kenneth Sauer Melvin P. Klein 《BBA》1984,767(2):209-216
Photosynthetic water oxidation by higher plants proceeds as though five intermediates, S0-S4, operate in a cyclic fashion. In this study of the manganese involvement in the process, a low temperature EPR signal is used as an indicator of S-state composition for manganese X-ray absorption K-edge measurements of a spinach Photosystem II preparation. A dramatic change is observed in the edge properties between samples prepared in states S1 and either S2 or S3, establishing a direct relation between the local environment of Mn and the S-state composition. Samples in S2 or S3 exhibit a broadening of the principal absorption peak and a shift to higher energy by as much as 2.5 eV relative to S1 samples. The magnitude of these changes is directly related to the EPR signal intensity induced by illumination. Models are discussed in which these data may be interpreted in terms of a conformation-induced change in Mn ligation and/or oxidation during the S1 to S2 transition. 相似文献