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21.
Factors Determining the Frequency of the Killer Trait within Populations of the Paramecium aurelia Complex 下载免费PDF全文
Wayne G. Landis 《Genetics》1987,115(1):197-205
The factors maintaining the cytoplasmically inherited killer trait in populations of Paramecium tetraurelia and Paramecium biaurelia were examined using, in part, computer simulation. Frequency of the K and k alleles, infection and loss of the endosymbionts, recombination during conjugation and autogamy, cytoplasmic exchange and natural selection were incorporated in a model. Infection during cytoplasmic exchange at conjugation and natural selection were factors that would increase the proportion of killers in a population. Conversely, k alleles reduced the proportion of killers in a population, acting through conjugation and autogamy. Field studies indicate that the odd mating type is prevalent in P. tetraurelia isolated from nature. Conjugation and therefore transmission by cytoplasmic transfer would be rare. Competition studies indicate a strong selective disadvantage for sensitives at concentrations found in nature. Natural selection must therefore be the factor maintaining the killer trait in P. tetraurelia. 相似文献
22.
Phytochrome-mediated germination of fern spores of Dryopteris paleacea Sw. was initiated by a saturating red-light (R) irradiation after 20 h of imbibition. For its realization external Ca2+ was required, with a threshold at a submicromolar concentration, and an optimum was reached around 10-4 M. At concentrations 10-1 M only a reduced response was obtained, based probably on an unspecific osmotic or ionic effect. The germination response was inhibited by La3+, an antagonist of Ca2+. From these results it is concluded that Ca2+ influx from the medium into the spores may be an important event in phytochrome-mediated germination. In the absence of Ca2+ the R-stimulated system remained capable of responding to Ca2+, added as late as 40 h after R. Moreover, Ca2+ was effective even if added after the active form of phytochrome, Pfr, had been abolished by far-red (FR) 24 h after R. Thus, the primary effect of Pfr, that initiates the transduction chain, does not require calcium. Coupling of Pfr to subsequent dark reactions has been investigated by R-FR irradiations with various dark intervals. The resulting escape kinetics were characterized by a lag phase (6 h) and half-maximal escape from FR reversibility (19 h). These kinetics were not significantly changed by the presence or absence of calcium. Thus, direct interaction of Pfr and calcium is not a step in the transduction chain initiated by the active form of photochrome.Abbreviations EGTA
ethyleneglycol-bis(-aminoethyl ether)-N,N,N,N-tetraacetic acid
- FR
far-red light
- Pr
red-light-absorbing form of phytochrome
- Pfr
far red-light-absorbing form of phytochrome
- Pipes
piperazine-1,4-bis(2-ethanesulfonic acid)
- R
red light
A preliminary report of this work was presented at the XIV Int. Bot. Congr., Berlin (West), Germany, Book of Abstracts, 2-116a-5 (1987) 相似文献
23.
24.
silver Wayne L.; Walker Dianne B.; Ogden Michael W.; Walker James C. 《Chemical senses》1990,15(6):701-712
An apparatus was developed which permits the automated deliveryof volatile chemical stimuli for use in neurophysiology experiments.A computer-controlled olfactometer, incorporating electronicmass flow controllers (EMFCs) and Teflon-lined solenoid valves,generated and delivered clean or odorized air. Neural and respiratorysignals from the animal were amplified and stored, along withtrial information (e.g. odorant concentration) on a chart recorderand video cassette recorder, both of which were controlled bythe computer. This apparatus was used to measure responses totoluene from the rat ethmoid nerve, a part of the ophthalmicdivision of the trigeminal nerve. Multi-unit responses to thiscompound were first observed at 2000 p.p.m. The magnitude ofthe response increased linearly with logarithmic increases inconcentration up to vapour saturation. Changes in respirationin response to toluene also were observed, although neural responsesoften were seen in the absence of respiratory changes. 相似文献
25.
Plasmid content of 5 hepatotoxin and 2 neurotoxin producing cyanobacterial strains were analyzed. Among the hepatotoxin-producing strains, Microcystis aeruginosa PCC7820, M. aeruginosa M228 and M. aeruginosa UV027 were found to carry plasmids, whereas other hepatotoxin and neurotoxin producing strains did not harbor any plasmids. Correlations were sought between toxicity and the presence of plasmids in toxic cyanobacteria as a function of age. Aged cultures of M. aeruginosa PCC7820 exhibited toxicity and harbored plasmids. In other cyanobacterial strains, plasmids were not detected. The data add to and support the current understanding that plasmids are probably not involved in toxin production in cyanobacteria.Author for Correspondence 相似文献
26.
Chromosomal localization of satellite DNA sequences among 22 species of felids and canids (Carnivora) 总被引:2,自引:0,他引:2
In situ hybridization was carried out using cloned satellite DNAs from the domestic cat and domestic dog as probes to metaphase chromosomes from 12 species of felids and 10 species of canids. Autoradiographic silver grains along metaphase chromosomes were counted and analyzed with regard to the mean number of grains per cell in each species, their chromosomal location, and their presence or absence on specific autosomes or sex chromosomes, where known. Among the felids and canids there was a 7.6- and 8.9-fold statistically significant difference, respectively, in the mean number of grains per cell between the species having the minimum and maximum values. Among the felids, most grains occurred on the telomeres of D- and E-group chromosomes, although departures from this general pattern also occurred. For example, the Asian golden cat and the Bornean bay cat showed substantial labeling at the centromeric region of chromosome A1, and a number of species showed some labeling at the short-arm telomeres of B-group chromosomes. Among the canids, about 90% of all grains were located at autosomal centromeres, and grains were absent from the sex chromosomes. Grains are usually distributed at chromosomal locations that stain C-band positive; however, certain C-band-positive regions without grains probably do not contain the particular satellites studied here. 相似文献
27.
Bruce Vondracek Wayne A. Wurtsbaugh Joseph J. Cech 《Environmental Biology of Fishes》1988,21(1):45-57
The allocation of energy to growth and reproduction, in relation to temperature and food availability, was investigated in
laboratory experiments with the mosquitofish,Gambusia affinis. At constant temperature of 20, 25 and 30°C and ad libitum feeding, specific growth rates increased with increasing temperature
at 1.7, 3.1 and 3.4% dry mass day−1, respectively. Growth rates in a cycling temperature regime (20–30°C,
) were faster than in a 25°C constant temperature. As temperature increased from 20 to 30°C, mean age at first reproduction
decreased from 191 to 56 days and brood size and mass of offspring increased significantly. Interbrood interval was also temperature
dependent; estimates at 25 and 30°C for females >1000 mg were 22.6 and 18.6 days, respectively. Interbrood interval could
not be calculated at 20°C. Although fitness was highest at 30°C, females at 25°C invested a greater proportion of surplus
energy (growth and reproduction) to reproduction (38%) than at 20 (17%) or 30°C (36%) during the 32-week study. Fish at cooler
temperatures began reproduction at a smaller size.
Where rations were controlled at low, medium, and ad libitum levels, somatic and gonadal growth increased with increasing
temperatures and food availability. The proportion of energy invested in reproduction was highest at 25°C for each comparable
ration level. Calculated energy budgets indicated that over the 10-week study, 17–22% of the food energy was invested in growth,
0–7% in reproduction, and 75–83% in respiration and excretory losses, depending on feeding and temperature conditions. 相似文献
28.
Roderick A. Capaldi Diego Gonzalez Halphen Yu-Zhong Zhang Wayne Yanamura 《Journal of bioenergetics and biomembranes》1988,20(3):291-311
There is a renewed interest in the structure and functioning of the mitochondrial respiratory chain with the realization that a number of genetic disorders result from defects in mitochondrial electron transfer. These so-called mitochondrial myopathies include diseases of muscle, heart, and brain. The respiratory chain can be fractionated into four large multipeptide complexes, an NADH ubiquinone reductase (complex I), succinate ubiquinone reductase (complex II), ubiquinol oxidoreductase (complex III), and cytochromec oxidase (complex IV). Mitochondrial myopathies involving each of these complexes have been described. This review summarizes compositional and structural data on the respiratory chain proteins and describes the arrangement of these complexes in the mitochondrial inner membrane. This biochemical information is provided as a framework for the diagnosis and molecular characterization of mitochondrial diseases. 相似文献
29.
Sources,fates, and impacts of nitrogen inputs to terrestrial ecosystems: review and synthesis 总被引:1,自引:0,他引:1
The relative importance of nitrogen inputs from atmospheric deposition and biological fixation is reviewed in a number of diverse, non-agricultural terrestrial ecosystems. Bulk precipitation inputs of N (l–l2 kg N ha–1 yr–1) are the same order of magnitude as, or frequently larger than, the usual range of inputs from nonsymbiotic fixation (< 1=" –=" 5=" kg=" n=">–1 yr–1), especially in areas influenced by industrial activity. Bulk precipitation measurements may underestimate total atmospheric deposition by 30–40% because they generally do not include all forms of wet and dry deposition. Symbiotic fixation generally ranges from 10–160 kg N ha–1 yr–1) in ecosystems where N-fixing species are present during early successional stages, and may exceed the range under unusual conditions.Rates of both symbiotic and nonsymbiotic fixation appear to be greater during early successional stages of forest development, where they have major impacts on nitrogen dynamics and ecosystem productivity. Fates and impacts of these nitrogen inputs are important considerations that are inadequately understood. These input processes are highly variable in space and time, and few sites have adequate comparative information on both nitrogen deposition and fixation.
相似文献
| - more intensive studies of total atmospheric deposition, especially of dry deposition, are needed over a wide range of ecosystems; |
| - additional studies of symbiotic fixation are needed that carefully quantify variation over space and time, examine more factors regulating fixation, and focus upon the availability of N and its effects upon productivity and other nutrient cycling processes; |
| - process-level studies of associative N-fixation should be conducted over a range of ecosystems to determine the universal importance of rhizosphere fixation; |
| - further examination of the role of free-living fixation in wood decomposition and soil organic matter genesis is needed, with attention upon spatial and temporal variation; and |
| - investigations of long-term biogeochemical impacts of these inputs must be integrated with process-level studies using modern modelling techniques. |
30.
A method is described to determine germination by blue-light excited red fluorescence in the positively photoblastic spores of Dryopteris paleacea Sw. This fluorescence is due to chlorophyll as evidenced from 1) a fluorescence-emission spectrum in vivo, where a bright fluorescence around 675 nm is obtained only in red light (R)-irradiated spores and 2) in vitro measurements with acetone extracts prepared from homogenized spores. Significant amounts of chlorophyll can be found only in R-treated spores; this chlorophyll exhibits an emission band around 668 nm, when irradiated with 430 nm light at 21°C.
Compared to other criteria for germination, such as swelling of the cell, coat splitting, greening, and rhizoid formation, which require longer periods after induction for their expression, chlorophyll fluorescence can be used to quantify germination after two days. This result is confirmed by fluence-response curves for R-induced spore germination; the same relationship between applied R and germination is obtained by the evaluation with the epifluorescence method 2 days after the light treatment as compared with the evaluation with bright-field microscopy 5 days after the inducing R.
Using this technique we show for the first time that Ca2+ contributes to the signaltransduction chain in phytochrome-mediated chlorophyll synthesis in spores of Dryopteris paleacea . 相似文献
Compared to other criteria for germination, such as swelling of the cell, coat splitting, greening, and rhizoid formation, which require longer periods after induction for their expression, chlorophyll fluorescence can be used to quantify germination after two days. This result is confirmed by fluence-response curves for R-induced spore germination; the same relationship between applied R and germination is obtained by the evaluation with the epifluorescence method 2 days after the light treatment as compared with the evaluation with bright-field microscopy 5 days after the inducing R.
Using this technique we show for the first time that Ca