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991.
Stéphan G. Reebs N. Mrosovsky 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1989,165(6):819-825
Summary Bouts of induced wheel-running, 3 h long, accelerate the rate of re-entrainment of hamsters' activity rhythms to light-dark (LD) cycles that have been phase-advanced by 8 h (Mrosovsky and Salmon 1987). The bouts of running are given early in the first night of the new LD cycle, and by the second night the phase advance in activity onset already averages 7 h. Such large shifts contrast with the mean phase advance of <1 h at the peak of the phase response curve when hamsters in constant darkness (DD) experience 2-h pulses of induced activity (Reebs and Mrosovsky 1989). The present paper investigates pulse duration and light as possible causes for the discrepancy in shift amplitude between these two studies. In a first experiment, pulses of induced wheel-running 1 h, 3 h, or 5 h long were given at circadian times (CT) 6 and 22-2 to hamsters free-running in DD. Pulses given at CT 6 caused phase-advances of up to 2.8 h, whereas pulses at CT 22-2 resulted in delays of up to 1.0 h. Shifts after 3-h and 5-h pulses did not differ, but were larger than after 1-h pulses, and larger than after the 2-h pulses given in DD by Reebs and Mrosovsky (1989). Thus 3 h appears to be the minimum pulse duration necessary to obtain maximum phase-shifting effects. In a second experiment, the re-entrainment design of Mrosovsky and Salmon (1987) was repeated with the light portion of the shifted LD cycle eliminated. Hamsters exercised for 3 h phase-advanced 2.9 h on average (excluding 2 animals who ran poorly). When the same hamsters were exposed 7 days later to a 14-h light pulse starting 5 h after their activity onset, they advanced by an average of 3.3 h. Adding the average values for activity-induced shifts and light-induced shifts gives a total of about 6 h. Possible synergism between the effects of induced activity and those of light may account for the remaining small difference between this total and the 7-h advances previously reported.Abbreviations
CT
circadian time
-
DD
constant darkness
-
LD
light-dark
-
PRC
phase response curve
-
free-running period of rhythm 相似文献
992.
Dr. Isabelle A. Carré Ady S. Oster Danielle L. Laval-Martin Leland N. Edmunds Jr. 《Current microbiology》1989,19(4):223-229
The photosynthesis-deficient ZC mutant ofEuglena gracilis Klebs (strain Z) was cultured at 16°C on an aerated, magnetically stirred, mineral medium containing 0.1% ethanol (pH 7.0). Cell division could be entrained by a 12: 12 light: dark cycle (LD: 12, 12) or even by a one-pulse skeleton photoperiod (LD: 1,23) The rhythm free-ran in DD for at least 8 days with a circadian period (=25.5 h) in populations that had been previously entrained by LD. The freerunning rhythm could be phase-shifted by a single 1-h light pulse (3000 lx). The strong (Type 0) phase-response curve derived from the resetting effects of such signals given at different circadian times was similar to that for the photosynthetic wild-type strain. These results demonstrate that the presence of a functional chloroplast compartment is not necessary for the circadian clock to function inEuglena and suggest that phase resetting of the circadian clock by light occurs via a similar pathway in both photosynthetic and non-photosynthetic cell types. 相似文献
993.
At temperatures lower than 37°C, the ethanol inhibition constant (Ki) for growth or fermentation inrho
+ cells of theSaccharomyces cerevisiae strain S288C was always higher (1.1M) than inrho
– mutants (0.7M). At 37°C these differences disappeared, and both strains were equally inhibited by ethanol (Ki=0.7m). Mitochondrial activity can be inhibited by high ethanol concentration and temperature. In fact, the stronger inhibition by ethanol of therho
+ strain at 37°C was due to the fact that, under these conditions, this strain loses the advantage conferred by mitochondrial activity since the induction ofrho
– cells in the population is very high. This does not result in an increase in the frequency ofrho
– mutants because of the poor viability of these mutants in conditions of high temperature and ethanol. In consequence, S288C strain becomes as strongly inhibited by ethanol as therho
– mutant strains. Differences in viability were not related to the fatty acids and ergosterol composition of the strain. In the presence of ethanol, bothrho
+ andrho
– strains modified their lipids in the same way, but these changes did not improve their ethanol tolerance. They were not due to differences in adaptation to ethanol either, since after successive transfers in ethanol, growth () and fermentation () rates in therho
– mutants were increasingly inhibited with time, whereas in the S288C strain inhibition of and by ethanol remained unaltered. Rather,rho
– mutants are less viable thanrho
+ cells because of the inability of the former to respire. At 37°C the Ki increased to 0.9M ethanol either when mitochondrial from highly ethanol-tolerant wine yeasts were transferred torho
– mutants of the strain S288C or when the mitochondria of strain S288C were preadapted by growing the strain in glycerol instead of glucose before it was cultivated in ethanol. 相似文献
994.
995.
996.
A Reinberg Y Motohashi P Bourdeleau Y Touitou J Nouguier J Nouguier F Lévi A Nicola? 《Chronobiologia》1989,16(1):21-34
Fifteen male subjects including 12 shift workers (oil refinery operators) volunteered to document circadian rhythms in sleep-wake, grip strength of both hands, peak expiratory flow, heart rate, self-rated drowsiness, fatigue and attention. Each of these variables was measured 4 to 6 times/day for 2 to 3 weeks. In addition, both axillary temperature (with a shielded probe) and wrist activity were almost continuously recorded at 15 min intervals during the same time span. Individual time series were analyzed according to several statistical methods (power spectrum, cosinor, chi 2, etc.), in order to estimate the prominent circadian period tau and to evaluate both individual and subgroup differences with regard to tolerance of shift work, age, duration of shift work. The present study confirms for continuously recorded temperature and wrist activity, grip strength of both hands, heart rate and peak expiratory flow that intolerance of shift work is frequently associated with an internal desynchronization. However, this conclusion cannot be extended to circadian rhythms in self-rated drowsiness, fatigue and attention. The internal desynchronization among several circadian rhythms supports the hypothesis that these latter are driven by several oscillators, with presumable differences between right and left hemispheres as suggested by unequal values of tau in rhythms of both hand grip strength. Since an internal desynchronization can be observed in tolerant shift workers having no complaint, it is likely that symptoms of intolerance are related to the subject's sensitivity to internal desynchronization rather than to the desynchronization itself. 相似文献
997.
Heterologous protein export in Escherichia coli: influence of bacterial signal peptides on the export of human interleukin 1 beta 总被引:2,自引:0,他引:2
P Denèfle S Kovarik T Ciora N Gosselet J C Bénichou M Latta F Guinet A Ryter J F Mayaux 《Gene》1989,85(2):499-510
Expression plasmids carrying the coding sequence of mature human interleukin 1 beta (IL 1 beta) linked either to a Met start codon, or fused to different efficient Escherichia coli secretion signal sequences, have been constructed. In the latter case, we used signal peptides derived either from an outer membrane protein (OmpA) or from a periplasmic protein (PhoA). The synthesis of IL1 beta from these fusions was investigated in an otherwise strictly isogenic context using identical conditions of derepression and culture media. The Met-IL1 beta fusion produced a soluble cytoplasmic protein which could be released from the cells by osmotic shock whereas the OmpA and PhoA fusions were always insoluble. The extent of sOmpA-IL1 beta maturation was found to vary from 50 to 100%, mainly depending on the medium used, whereas no significant maturation of the signal peptide could be detected in the case of the sPhoA-IL1 beta fusion. Immuno-electron microscopy revealed that the sOmpA-IL1 beta fusion was targeted to the inner membrane, whereas the sPhoA-IL1 beta fusion remained within the cytoplasm and thus did not appear to enter the secretion pathway. Amplifying the E. coli signal peptidase lep gene on a multicopy plasmid did not improve signal peptide removal from sOmpA-IL1 beta. Moreover, these E. coli secretion vectors allowed us to produce, in high levels, IL1 beta fragments which otherwise could not be stably accumulated within the cytoplasmic compartment. 相似文献
998.
The greening of the upper part of the outerAllium cepa L. bulb scales, in particular along the vascular regions, is limited to the hypodermal cells in which typical leucoplasts are transformed to normal and functional chloroplasts. This process is light dependent and cannot afterwards be reversed or modified by darkness. The changes in fine structure are described and briefly discussed.Dedicated to Prof. DrLothar Geitler on the occasion of his 90th birthday and 55 years after the publication of his Grundriß der Cytologie. 相似文献
999.
繁缕(Stellaria media)和小繁缕(S.apetala)是两个形态相似的近缘种,有人把后者作为前者的亚种或变种来处理。本文通过对南京地区不同生境的三个自然群体和三个人工控制栽培群体的取样,以群体为单位,分别测算了叶、萼片、雄蕊、花瓣、果实和种子的8个数量性状的变异,绘制了多角形图;对花粉粒和种子进行了扫描;还通过花蕾套袋试验对种子活力作了检查。结果发现繁缕和小繁缕都是近亲繁殖植物,在形态上区别明显,对生态环境的要求基本相同,但小繁缕似更能耐受人为的践踏和刈割。 相似文献
1000.
陕西蓝田公王岭“蓝田伟猴”化石的再研究 总被引:8,自引:4,他引:4
蓝田公王岭动物群中,唯一的一种非人灵长类化石由胡长康、齐陶(1978)定名为Megamacaca lantianensis(蓝田伟猴)。但按其形态,我们觉得把它归于疣猴亚科比较适宜。特别是与该亚科中的金丝猴属(Rhinopithecus)更为相像,例如蓝田标本下颌支与下颌体垂直,冠状突略向后弯,齿尖起伏较大等都显示了金丝猴的一般性质。至此,本文将蓝田伟猴归于金丝猴属,保留原有种名:Rhinopithecus(Megamacaca)lantianensis(Hu and Qi)。时代为早更新世晚期。 相似文献