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61.
GUY JUMARIE 《Journal of biological physics》1997,23(2):101-110
In the information theoretic framework, to some extent, the complexity ofa system can be measured by its informational divergence which is thedifference between the maximum possible value of its entropy and theactual value of the latter. In her analysis of the DNA chain, Gatlinput in evidence two different divergences. One which drops the mutualdependences between the bases (A, C, G, T) and the other one whichexplicitly refers to this dependence via conditional entropies, and thus,provides a measure of the structural complexity of the system. One showshow the explicit form of this structural divergence can be obtained fordiscrete and continuous Markovian stochastic processes, and in the lattercase, as expected, this divergence is invariant under a transformation ofvariables. 相似文献
62.
G. BRUGEROLLE et G. METENIER 《The Journal of eukaryotic microbiology》1973,20(2):320-327
RESUME. Deux formes d'activité malate-deshydrogénasique (MDH) ont été séparées après centrifugation en gradient de densité, chez Trichomonas vaginalis: une forme est soluble et l'autre est liée aux "grains denses'cytoplasmiques. Ces 2 MDH (NAD dépendantes) ont des pH d'activité optimale et des constantes de Michaelis différents; on peut les séparer par électrophorèse sur gel d'amidon ou de polyacrylamide (présence d'isoenzymes).
SYNOPSIS. Two forms (isozymes) of malate dehydrogenase (MDH) of Trichomonas vaginalis cells were isolated by centrifugation on sucrose density gradient. One form is located in the soluble fraction and the other is linked to the cytoplasmic "dense granules."
The optimum pH and Km values are different for the 2, NAD-dependent dehydrogenases, which can be separated by starch or polyacrylamide gel electrophoresis. 相似文献
SYNOPSIS. Two forms (isozymes) of malate dehydrogenase (MDH) of Trichomonas vaginalis cells were isolated by centrifugation on sucrose density gradient. One form is located in the soluble fraction and the other is linked to the cytoplasmic "dense granules."
The optimum pH and K
63.
GUY METENIER 《The Journal of eukaryotic microbiology》1978,25(3):326-334
RÉSUMÉ. Des expérimentations portant sur des cellules isolées ont montré que 77% des microstomes de Tetrahymena paravorax, prélevés au hasard dans des cultures en phase logarithmique de croissance, se transforment directement en macrostomes en présence de “stomatine.” Ces macrostomes apparaissent à des moments variés entre 1,5 et 9 h après l'addition de la stomatine (“point 50% de transformations” vers 2,5 h). La compétence pour le remplacement oral est en relation avec la position dans le cycle cellulaire. Les pourcentages de transformation les plus élevés sont observés avec les populations testées pendant la première moitié de la période moyenne d'interfission. La formation des macrostomes est d'autant plus rapide que l'ǎge initial des microstomes est plus proche du point médian du cycle cellulaire (“point de compétence”). Dans la seconde moitié de ce cycle, le temps moyen de transformation reste à peu près constant, mais le pourcentage de divisions augmente: le “point de transition” (50% de divisions) se trouve au début d'une phase terminale représentant 19–20% de la durée totale du cycle. La transformation des produits de bipartition antérieur et postérieur est nettement asynchrone: dans la majorité des paires cellulaires, l'opisthe se transforme avant le proter. Les cellules-soeurs se divisent aussi de manière asynchrone: le temps de génération du proter est plus long que celui de l'opisthe. Le problème de l'acquisition de la compétence pour le changement de phénotype est discuté en envisageant les corrélations éventuelles avec certains processus majeurs du cycle cellulaire. SYNOPSIS. Seventy-seven percent of the microstomes of Tetrahymena paravorax taken from random samples of log-phase cultures transform directly into macrostomes in the presence of “stomatin.” These macrostomes appear between 1.5 and 9 h after addition of stomatin (“50% transformation point,”~ 2.5 h). Competence for oral replacement is related to the position in the cell cycle. The highest percentages of transformation are observed in populations tested during the first half of the mean interfission period. Formation of macrostomes is more rapid when the initial age of the microstomes is nearer to the midpoint of the cell cycle (“competence point”). In the 2nd half of this cycle, the mean transformation time remains approximately constant, but the percentage of cells undergoing division is increasing. The “transition point” (50% divided cells) is found at the beginning of a terminal phase which accounts for 19–20% of the cell cycle. Transformation of anterior and posterior fission products is fairly asynchronous; in the majority of individual pairs, the opisthe is transformed before the proter. The daughter cells also divide asynchronously, the generation time of the proter being longer than that of the opisthe. The problem of acquisition of competence for phenotypic change is discussed in light of possible correlations with certain major processes of the cell cycle. 相似文献
64.
Photoadaptation, photoinhibition and productivity in the blue-green alga, Spirulina platensis grown outdoors 总被引:2,自引:0,他引:2
Two Spirulina platensis strains, SP-G and SP-RB, resistant and sensitive to photoinhibition of photosynthesis, respectively, were grown outdoors in dense cultures and under different photon fluxes provided by shading. Cultures of both strains grown under full sunlight were more resistant to photoinhibition than those grown under nets with 15–50% decreases in the incident photon flux. Cultures grown outdoors were more resistant to photoinhibition than the laboratory ones. At noon, the photosynthetic activity, as expressed by O2 evolution, was higher for cultures grown under 50% shade, as compared with unshaded cultures. Productivity of the shaded cultures, in terms of biomass produced per day, was always higher when the cultures were protected from photoinhibition. 相似文献
65.
RAJU Y. SOOLANAYAKANAHALLY ROBERT D. GUY SALIM N. SILIM ERIC C. DREWES & WILLIAM R. SCHROEDER 《Plant, cell & environment》2009,32(12):1821-1832
In outdoor common gardens, high latitude populations of deciduous tree species often display higher assimilation rates ( A ) than low latitude populations, but they accomplish less height. To test whether trends in A reflect adaptation to growing season length or, alternatively, are garden growth artefacts, we examined variation in height increment and ecophysiological traits in a range-wide collection of Populus balsamifera L. populations from 21 provenances, during unconstrained growth in a greenhouse. Rooted cuttings, maintained without resource limitation under 21 h photoperiod for 90 d, displayed increasing height growth, A , leaf mass per area and leaf N per area with latitude whereas stomatal conductance ( g s ) showed no pattern. Water-use efficiency as indicated by both gas exchange and δ 13 C increased with latitude, whereas photosynthetic nitrogen-use efficiency decreased. Differences in δ 13 C were less than expected based on A/g s , suggesting coextensive variation in internal conductance ( g m ). Analysis of A – C i curves on a subset of populations showed that high latitude genotypes had greater g m than low-latitude genotypes. We conclude that higher peak rates of height growth in high latitude genotypes of balsam poplar are supported by higher A , achieved partly through higher g m , to help compensate for a shorter growing season. 相似文献
66.
NATHAN R. FRANSSEN KEITH B. GIDO CHRISTOPHER S. GUY JEFF A. TRIPE SALLY J. SHRANK TIMOTHY R. STRAKOSH KATIE N. BERTRAND COURTNEY M. FRANSSEN KRISTEN L. PITTS CRAIG P. PAUKERT 《Freshwater Biology》2006,51(11):2072-2086
1. Floods are major disturbances to stream ecosystems that can kill or displace organisms and modify habitats. Many studies have reported changes in fish assemblages after a single flood, but few studies have evaluated the importance of timing and intensity of floods on long‐term fish assemblage dynamics. 2. We used a 10‐year dataset to evaluate the effects of floods on fishes in Kings Creek, an intermittent prairie stream in north‐eastern, Kansas, U.S.A. Samples were collected seasonally at two perennial headwater sites (1995–2005) and one perennial downstream flowing site (1997–2005) allowing us to evaluate the effects of floods at different locations within a watershed. In addition, four surveys during 2003 and 2004 sampled 3–5 km of stream between the long‐term study sites to evaluate the use of intermittent reaches of this stream. 3. Because of higher discharge and bed scouring at the downstream site, we predicted that the fish assemblage would have lowered species richness and abundance following floods. In contrast, we expected increased species richness and abundance at headwater sites because floods increase stream connectivity and create the potential for colonisation from downstream reaches. 4. Akaike Information Criteria (AIC) was used to select among candidate regression models that predicted species richness and abundance based on Julian date, time since floods, season and physical habitat at each site. At the downstream site, AIC weightings suggested Julian date was the best predictor of fish assemblage structure, but no model explained >16% of the variation in species richness or community structure. Variation explained by Julian date was primarily attributed to a long‐term pattern of declining abundance of common species. At the headwater sites, there was not a single candidate model selected to predict total species abundance and assemblage structure. AIC weightings suggested variation in assemblage structure was associated with either Julian date or local habitat characteristics. 5. Fishes rapidly colonised isolated or dry habitats following floods. This was evidenced by the occurrence of fishes in intermittent reaches and the positive association between maximum daily discharge and colonisation events at both headwater sites. 6. Our study suggests floods allow dispersal into intermittent habitats with little or no downstream displacement of fishes. Movement of fishes among habitats during flooding highlights the importance of maintaining connectivity of stream networks of low to medium order prairie streams. 相似文献
67.
RAJU Y. SOOLANAYAKANAHALLY ROBERT D. GUY SALIM N. SILIM MINGHUA SONG 《Plant, cell & environment》2013,36(1):116-127
Plant phenology is expected to be sensitive to climate warming. In boreal trees, spring flush is primarily temperature driven, whereas height growth cessation and autumn leaf senescence are predominantly controlled by photoperiod. Cuttings of 525 genotypes from the full range of balsam poplar were planted into two common gardens (Vancouver and Indian Head, Canada) at similar latitudes, but with differing winter temperatures and growing seasons. There was clinal variation in spring and, particularly, summer and fall phenology. Bud flush and, despite milder climate, bud set and leaf drop were earlier at Vancouver than at Indian Head by 44, 28 and 7 d, respectively. Although newly flushed growth is insensitive to photoperiod, many genotypes at both sites became competent before the summer solstice. At Vancouver, high‐latitude genotypes set dormant terminal buds in mid‐spring. Most other genotypes grew until midsummer or set bud temporarily and then experienced a second flush. In both gardens and in a growth chamber experiment, earlier bud set was associated with reduced height growth and higher root/shoot ratios. Shoots attained competency ~5 weeks after flushing, which would normally prevent dormancy induction before the solstice, but may be insufficient if spring advances by more than a few weeks. 相似文献
68.
According to what we call the Principle of Procreative Beneficence (PB), couples who decide to have a child have a significant moral reason to select the child who, given his or her genetic endowment, can be expected to enjoy the most well-being. In the first part of this paper, we introduce PB, explain its content, grounds, and implications, and defend it against various objections. In the second part, we argue that PB is superior to competing principles of procreative selection such as that of procreative autonomy. In the third part of the paper, we consider the relation between PB and disability. We develop a revisionary account of disability, in which disability is a species of instrumental badness that is context- and person-relative. Although PB instructs us to aim to reduce disability in future children whenever possible, it does not privilege the normal. What matters is not whether future children meet certain biological or statistical norms, but what level of well-being they can be expected to have. 相似文献
69.
1. Parasitic wasps with structured populations are generally assumed to follow the local mate competition (LMC) model: females lay only the minimal number of sons necessary to inseminate all daughters in the emergence patch, and increase this number when faced with additional broods from unrelated females. After emergence, daughters mate with local males before dispersing for host location and oviposition. The main predictions from the model have been verified for many species. 2. Conflicting evidence exists on the status of the egg parasitoids Trichogramma regarding their on‐patch versus off‐patch mating. Although the life‐history traits of several species indicate that mating must occur on the emergence patch, recent data suggest that mating could occur outside the natal patch. 3. In this study, we measured the level of off‐patch mating in the egg parasitoid Trichogramma euproctidis using two isofemale lines in a greenhouse experiment. The impact of the sex ratio on the level of off‐patch mating was also tested. 4. The overall off‐patch mating proportion was 40.5% with a range between 0 and 85.7%, and was influenced by the sex ratio on the emergence patch: the more males available at emergence, the less off‐patch mating occurring. 5. The mating structure of this species can be described as partial LMC. 相似文献
70.