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1.
Variability in DNA content to testis cells and sperm from F1 hybrids between the laboratory mouse (M. muscullus) and the tobacco mouse (M. poschiavinus), has been determined by flow cytometry (FMC). The F1 hybrid mouse is known to be heterozygous for seven metacentric chromosomes produced by Robertsonian fusion. Enriched populations of nuclei from late pachytene spermatocytes and round spermatids were obtained by velocity sedimentation. These nuclei, as well as epididymal sperm nuclei and spleen cells, were stained by the acriflavin-Feulgen technique for DNA and measured by FCM. Peaks in the fluorescence intensity frequency distributions resulting from these measurements were analyzed to determine their mean fluorescence intensities and their widths (coefficients of variation). Because mean intensities of corresponding cell types from M. musculus and the F1 hybrids were identical, the average DNA contents were taken to be the same. The average coefficients of variation of the peaks to fluorescence from the pachytene, spermatid, and sperm nuclei and spleen cells from M. muscullus animals were about 5%. While the peaks of fluorescence from spleen cells and pachytene nuclei from f1 hybrids also had average coefficients of variation of 5%, post-meiotic nuclei from spermatids and spermatozoa had coefficients of variationof 8%. From these results we conclude that, in these F1 hybrids, abnormal meiotic segregation causes an increased variability of 6% in the amount of DNA in the spermatozoa.  相似文献   

2.
When exposed to light, the cells of characean algae produce intermittent regions of H+ extrusion and H+ absorption, featuring different photosynthetic activities. Methods for local measurements of outer pH, O2 content, and photochemical activity of photosystem II (PSII) were applied to examine microscopic regions of Chara coralline Klein ex Willd. internodes. The results show that the functional spatial heterogeneity of these excitable cells is controlled not only by light but also by electric excitation of the plasma membrane. Generation of a single action potential (AP) induced a reversible transition to the state with homogenous pH distribution and had different effects on photosynthesis in cell regions producing alkaline and acid zones. The effective quantum yield of PSII primary processes and the maximal chlorophyll fluorescence decreased after AP in the alkaline cell regions but were almost unaffected in the acidic cell regions. The suppression of photosynthesis after AP was also evident in the decrease of photosynthetic O2 evolution. The results provide evidence that electric signals arising at the plasmalemma are transmitted to the level of thylakoid membranes. The effects of electric excitation on fluorescence and the quantum yield of PSII photochemistry were best pronounced at low light intensities and low level of nonphotochemical quenching. The sensitivity of chlorophyll fluorescence in resting and excited cells to light intensity and protonophores indicates that the AP-induced fluorescence changes derive from the increase in pH gradient at the thylakoid membrane. The temporal elimination of alkaline zones and inhibition of photosynthesis apparently arise from parallel operational sequences that have a common initial stage. A possible role of cytosolic Ca2+ rise in the mechanism of photosynthesis suppression after electric excitation of the plasma membrane is discussed.  相似文献   

3.
When orientation is attained under the influence of beams of parallel light opposed at 180° the deflection θ from a path at right angles to the beams is given by tan See PDF for Equation, where I 1 and I 2 are the photic intensities and H is the average angle between the photoreceptive surfaces. This expression is independent of the units in which I is measured, and holds whether the primary photosensory effect is proportional to I or to log I. When photokinetic side-to-side motions of the head occur, H decreases with increasing total acting light intensity, but increases if higher total light intensity restricts the amplitude of random movements; in each case, H is very nearly proportional to log I 1 I 2. For beams of light at 90°, See PDF for Equation. The application of these equations to some particular instances is discussed, and it is shown why certain simpler empirical formulæ previously found by others yield fair concordance with the experimental data. The result is thus in complete accord with the tropism theory, since the equations are based simply on the assumption that when orientation is attained photic excitation is the same on the two sides.  相似文献   

4.
Photosynthetic efficiency, primary productivity, and N2 reduction were determined in peas (Pisum sativum L. var. Alaska) grown at light intensities ranging from severely limiting to saturating. Plants grown under higher light intensities showed greater carboxylation and light capture potential and higher rates of net C exchange. Uptake of N2, computed from measured C2H2 reduction and H2 evolution rates, also increased with growth light intensity, while the previously proposed relative efficiency of N2 fixation, based on these same parameters, declined. The plot of N/C ratios (total nitrogen content/plant dry weight) increased hyperbolically with light intensity, and the plot of N2/CO2 uptake ratios (N2 uptake rate/net CO2 uptake rate) increased linearly. Both plots extrapolated to the light compensation point. The data indicate that the relative efficiency of N2 fixation is not necessarily correlated with maximum plant productivity and that evaluation of a plant's capacity to reduce N2 is related directly to concurrent CO2 reduction. A measure of whole plant N2 fixation efficiency based on the N2/CO2 uptake ratio is proposed.  相似文献   

5.
Stable hydrogen isotope ratios of wood lignin methoxy groups (δ2HLM values) of mid-latitude forests are increasingly applied to reconstruct δ2H patterns in precipitation of regional to sub-continental scales. To date, the knowledge about the effect of topographic factors on δ2HLM values is still scare, especially in the biogeographic boundary. We measured tree-ring δ2HLM chronologies (1901–2018) from two typical conifer species at three sites with different altitudes of a north-ridge-south transect of the Qinling Mountains (central China), where covers the climate transition zone from warm temperate to subtropics. The δ2HLM chronologies of the north and the south slopes were characterized by a decreasing trend between 1901 and 1955, which turned into a positive trend after 1955. In contrast, the mountain ridge site located at the highest altitude showed continuous increasing δ2HLM values over the entire period from 1901 to 2018. The highest correlations between temperature and δ2HLM chronologies were found for the northern slope and the mountain ridge region spring temperatures (March–May). The observed abrupt changes in the δ2HLM values since the 1950s at lower elevation sites might reveal slope-related moisture effects which superimpose local temperature patterns. During the rapidly warming period 1955–2018, the higher correlations of the δ2HLM chronologies with the spring and mean annual (previous November to current October) temperatures were detected on the warmer northern slope. In summary, although the variations of measured δ2HLM of the three investigated sites reflect geographic-specific hydrological characteristics, the low-frequency temperature changes are documented in the δ2HLM values.  相似文献   

6.
The reversible hydrogenase from Anabaena 7120 appeared when O2 was continuously removed from a growing culture. Activity increased further when cells were incubated under argon in the dark or in the light plus 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Hydrogenase existed in an inactive state during periods of O2 evolution. It could be reductively activated by exposure to reduced methyl viologen or by dark, anaerobic incubation. Hydrogenase-containing cells evolved H2 slowly during dark anaerobic incubations, and the rate of H2 evolution was increased by illumination with low intensity light. Light enhancement of H2 evolution was of short duration and was eliminated by the ferredoxin antagonist disalicylidene diaminopropane. Physiological acceptors that supported H2 uptake included NO3, NO2, and HSO3, and light had a slight influence on the rate of H2 uptake with these acceptors. Low levels of O2 supported H2 uptake, but higher concentrations of O2 inactivated the hydrogenase. Hydrogen uptake with HCO3 as acceptor was the most rapid reaction measured, and it was strictly light-dependent. It occurred only at low light intensities, and higher light intensities restored normal O2-evolving photosynthesis. It is suggested that hydrogenase is present to capture exogenous H2 as a source of reducing equivalents during growth in anaerobic environments.  相似文献   

7.
Flicker response curves have been obtained at 21.5°C. for three genera of fresh water teleosts: Enneacanthus (sunfish), Xiphophorus (swordtail), Platypoecilius (Platy), by the determination of mean critical intensities for response at fixed flicker frequencies, and for a certain homogeneous group of backcross hybrids of swordtail x Platy (Black Helleri). The curves exhibit marked differences in form and proportions. The same type of analysis is applicable to each, however. A low intensity rod-governed section has added to it a more extensive cone portion. Each part is accurately described by the equation F = Fmax./(1 + e -p log-p logI/Ii), where F = flicker frequency, I = associated mean critical intensity, and Ii is the intensity at the inflection point of the sigmoid curve relating F to log I. There is no correlation between quantitative features of the rod and cone portions. Threshold intensities, p, Ii, and Fmax. are separately and independently determined. The hybrid Black Helleri show quantitative agreement with the Xiphophorus parental stock in the values of p for rods and cones, and in the cone Fmax.; the rod Fmax. is very similar to that for the Platy stock; the general level of effective intensities is rather like that of the Platy form. This provides, among other things, a new kind of support for the duplicity doctrine. Various races of Platypoecilius maculatus, and P. variatus, give closely agreeing values of Im at different flicker frequencies; and two species of sunfish also agree. The effect of cross-breeding is thus not a superficial thing. It indicates the possibility of further genetic investigation. The variability of the critical intensity for response to flicker follows the rules previously found to hold for other forms. The variation is the expression of a property of the tested organism. It is shown that, on the assumption of a frequency distribution of receptor element thresholds as a function of log I, with fluctuation in the excitabilities of the marginally excited elements, it is to be expected that the dispersion of critical flicker frequencies in repeated measurements will pass through a maximum as log I is increased, whereas the dispersion of critical intensities will be proportional to Im; and that the proportionality factor in the case of different organisms bears no relation to the form or position of the respective curves relating mean critical intensity to flicker frequency. These deductions agree with the experimental findings.  相似文献   

8.
The Raman spectra of all the dimethylene interrupted methyl cis, cis-octadecadienoates and octadecadiynoates have been studied. The Raman band positions and their relative intensities for the ν(CC), ν(CC), ν(CO), ν(CH) and δ(CH2) modes are recorded. The height intensity of the bands arising from ν(CC) relative to ν(CO) provides a means of determining the number of cis-ethylenic bonds in a mono-ester. In the acetylenic series, the intensity of the bands arising from ν(CC) relative to ν(CO) failed to indicate with certainty the number of acetylenic bonds in the mono-esters studied, due to the weak intensity of the band due to ν(CO). However a better correlation between the relative intensities of the ν(CC) and δ(CH2) bands is established instead. An attempt to correlate the areas under the bands due to ν(CC), (CC), (CO) and δ(CH2) failed to produce any significant results. The Raman spectra of the methyl octadec-cis-10-en-5-ynoate and methyl octadeca-5, 10-diynoate are also recorded.  相似文献   

9.
The micellar properties of gangliosides in water solutions were investigated by quasielastic light scattering measurements. GM1 and GD1a gangliosides were isolated from calf brain, purified to more than 99% and dissolved in 0.025 M Tris—HCI buffer (pH 6.8) at 37°C. The average intensity of scattered light and the intensity correlation function were measured by an apparatus including a 5145 Å argon laser and a real-time digital correlator. The scattered intensity data allowed the derivation of an upper limit to the critical micelle concentration (c0) and the evaluation of the molecular weight (M) of the micelle. The intensity correlation function gave the diffusion coefficient D, and hence the hydrodynamic radius RH, and also contained information on the polydispersity of the sample. We find co < 1 × 10?6 M for both GM1 and GD1a, M = 532 000 ± 50 000 and RH = 63.9 ± 2 A? for GM1, and M = 417 000 ± 40 000 and RH = 59.5 ± 2 A? for GD1a. The mixture 3:1 of the two gangliosides gave intermediate values for all examined parameters. The presence of cations, within the physiological concentration range. and, in particular of Ca2+, did not influence significantly the values of co and the main features of the micelle.  相似文献   

10.
In order to elucidate the mobilities of the fluorophores of fluorescent 2- and 16-(9-anthroyloxy)palmitic acids (16-AP and 2-AP, respectively) in lipid bilayer vesicles, the steady-state and time-dependent nuclear Overhauser effects in 1H-NMR spectroscopy, but not the fluorescence depolarization in fluorescence spectroscopy, have been measured. The steady-state nuclear Overhauser effect measurements showed an appreciable magnitude of negative nuclear Overhauser effects between the resonances due to the fluorophores of the two fluorescent probes and lipids. These results definitely mean that in lipid bilayers, the fluorophores (anthroyloxy ring) of the fluorescent probes experience other types of motions with much longer correlation times than those detected by the fluorescence depolarization measurements, since at the correlation time showed by the fluorescent method (1–2 · 10−9 s or less), no such transfer of the negative nuclear Overhauser effects is expected to occur. The correlation times of the fluorophores, as calculated from the cross-relaxation rates of the anthroyl ring protons of 16-AP and 2-AP, were 3.8 · 10−8 and 1.1 · 10−7 s, respectively. These values, respectively, compare favorably with those of the terminal methyl of acyl chains and the choline methyl carbons which were estimated by 13C T2 relaxation times. Thus, it is concluded that the fluorophores of both 16-AP and 2-AP have a slow form of motion which moves with a similar time scale to those of lipids in addition to the faster one that causes fluorescence depolarization.  相似文献   

11.
Iodide and acrylamide were applied simultaneously in a doublequenching experiment to compare acrylamide quenching constants for internal and external fluorophores of high-density lipoproteins (HDL1 and HDL2) from manganese-adequate (MnA) and deficient (MnD) rats, free of the electrostatic effects associated with iodide. In MnA HDL1 compared to MnD HDL1, the acrylamide quenching constant for external fluorophores was different (P < 0.1). In MnA HDL2, there were two populations of fluorophores accessible to acrylamide, whereas in MnD HDL2, all fluorophores were accessible to both quenchers. We concluded that there were structural (local environmental) differences, possibly charge-related, around the external fluorophores, and a slightly larger population of buried fluorophores in the MnD HDL1 compared with MnA HDL1. In MnA HDL2, one-third of the fluorophores were accessible to iodide, and all external and internal fluorophores were accessible to acrylamide, whereas in MnD HDL2, all fluorophores were accessible to both quenchers.  相似文献   

12.
Y. Koyama  R.A. Long  W.G. Martin  P.R. Carey 《BBA》1979,548(1):153-160
The resonance Raman spectrum of the carotenoid neurosporene is shown to be a sensitive monitor of absorption shifts, and thus changes in membrane potential, in chromatophores of the GlC mutant of Rhodopseudomonas sphaeroides. For a Raman excitation wavelength at 472.7 nm, the intensities of the two most prominent resonance Raman features (v1 and v2) respond very differently to small shifts in the absorption maxima. Thus, the ratio intensity v1/intensity v2 is a sensitive probe for absorption shifts. Changes in this ratio of ~20% were observed during a valinomycin induced diffusion potential. At 5°C changes in the average intensity ratio of +6, ?4 and ?14% were brought about by oligomycin, FCCP and sodium deoxycholate, respectively. The changes in intensity ratio were temperature dependent and, in addition, effects due to the laser beam acting as an actinic light could be detected. Oscillatory changes were observed in absolute Raman and Rayleigh scattering intensities for chromatophores at 5°C and for intact cells under growing conditions.  相似文献   

13.
This study compared different measures of urban heat island (UHI) intensity, which were calculated using both air temperature (Tair) at a height of 1.5 m and Landsat land surface temperature (LST) in Hangzhou, China. Two UHI-driven indicators (range and magnitude) and two land-cover-driven indicators (urban-rural and urban-agriculture) were calculated to quantify the UHI intensity based on hourly Tair from five stations and fifteen Landsat 5 LST images. Pearson correlation testing and a moving average times series of the previous 30 days were used to investigate the relationship between UHI intensities calculated by different indicators and data. The results indicate that the land-cover-driven indicators explain UHI better than the UHI-driven indicators, while the calculated values of UHI intensity using Landsat LST and hourly Tair are not comparable. We also investigated the influence of weather conditions on UHI intensity. Generally, Landsat-LST-based UHI performs best on hot sunny days, while Tair-based UHI has a better chance during the nighttime following a dry sunny day. This study suggests that the value of UHI intensity can be influenced by the selected indicators, the data used, the acquisition time and the weather conditions. Thus, these factors should be considered when comparing UHI intensity between different cities or quantifying their influences (e.g., population size, land use and land cover change) on UHI intensity.  相似文献   

14.
The effect of two strains of the phytopathogenic fungus Septoria nodorum Berk. of different virulence on the intensity of local generation of hydrogen peroxide in common wheat leaves and the role of oxidoreductases in this process was studied. Differences in the pattern of hydrogen peroxide production in wheat plants infected with high- and low-virulence pathogen strains have been found. The low-virulent S. nodorum strain caused a long-term hydrogen peroxide (H2O2) generation in the infection zone, whereas the inoculation of leaves with the highly virulent strain resulted in a transient short-term increase in the H2O2 concentration at the initial moment of contact between the plant and the fungus. It was shown that the low level of H2O2 production by plant cells at the initial stages of pathogenesis facilitates S. nodorum growth and development. The decrease in the H2O2 concentration induced by the highly virulent S. nodorum strain is determined by inhibition of the oxalate oxidase activity in plant tissues and by the ability of the fungus to actively synthesize an extracellular catalase. The pattern of hydrogen peroxide generation at the initial stages of septoriosis may serve as an index of virulence of S. nodorum population.  相似文献   

15.
A theory describing the shapes of polarized fluorescence photobleaching recovery (PFPR) curves for a population of fluorophores undergoing restricted rotational diffusion in two-dimensional systems such as planar membranes has been developed. In this model, restricted rotational diffusion of the fluorophores is described by using reflective boundary conditions, in which the fluorophores are assumed to diffuse freely but only within an angular space of width 2ω. The magnitude and apparent rate of the PFPR postbleach fluorescence curves are a function of both ω and the angle between the bleaching and observation beam polarizations ψ. It is shown that estimates of the degree of rotational restriction ω may be obtained from changes in the ψ-dependent postbleach fluorescence intensities. Using angle-dependent PFPR, slow rotational reorientations of the fluorescent lipid analogue 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine in distearoylphosphatidylcholine Langmuir–Blodgett monolayers deposited on octadecyltrichlorosilane-treated fused quartz were measured. As theoretically predicted for a rotationally restricted fluorophore population, both the initial Fψ(0) and final Fψ(∞) postbleach fluorescence intensities varied as a function of ψ, and no measurable change in the postbleach fluorescence intensities was observed for ψ = 45°. Using the theory for restricted rotational motion, the ψ-dependent variations of the final fluorescence intensities Fψ(∞) obtained at two bleaching intensities gave an average apparent ω ≈? 52°. However, to adequately fit the Fψ(0) data, inclusion of the theoretical effects of rapid (faster than the duration of the photobleaching pulse) fluorophore dynamics was also required. Best fits of the Fψ(0) and Fψ(∞) data were obtained when the fluorophores were assumed to rapidly wobble within a cone of semiangle δ ≈? 30°–50° while slowly rotating within an angular space defined by semiangle ω ≈? 35°–60°. Subsequent analysis of the time- and ψ-dependent changes in the postbleach fluorescence curves Fψ(t) gave apparent diffusion coefficients ranging from D ≈? 10?3 s?1 to 4 × 10?2 s?1. © 1993 John Wiley & Sons, Inc.  相似文献   

16.
L. K. Matveeva 《Hydrobiologia》1983,104(1):353-356
Seasonal changes of species diversity (Hr) and average spatial overlap (ōjk) of planktonic rotifers in a mesotrophic lake were examined with respect to their dependence on habitat diversity (Hh) and on a predator (Asplanchna herricki). Hr was positively correlated with the density of A. herricki and with Hh. In the absence of A. herricki there was no correlation between Hr and Hh. ōjk was negatively correlated with the density of A. herricki and with Hh; the correlation between ōjk and Hh was independent of the presence of the predator.  相似文献   

17.
Trait matching—a correlation between the morphology of plants and their pollinators—has been frequently observed in pollination interactions. Different intensities of natural selection in individual regions should cause such correlations to be observable across different local assemblages. In this study, we focused on matching between spur lengths of the genus Impatiens and bill lengths of sunbirds in tropical Africa. For 25 mountain and island locations, we compiled information about the composition and traits of local Impatiens and sunbird assemblages. We found that assemblage mean and maximum values of bill lengths were positively correlated with mean and maximum spur lengths across locations. Moreover, our results suggest that the positive correlations hold only for forest sunbird assemblages sharing the same habitat with Impatiens species. We further show that long‐billed sunbirds seem to locally match the morphology of multiple Impatiens plant species, not vice versa. Our observation implies that trait matching significantly contributes to structuring of Impatiens–sunbird pollination systems. We suggest that special habitat preferences together with spatial isolation of mountain environment might play a role in this case.  相似文献   

18.
In photosynthetic organisms, sudden changes in light intensity perturb the photosynthetic electron flow and lead to an increased production of reactive oxygen species. At the same time, thioredoxins can sense the redox state of the chloroplast. According to our hypothesis, thioredoxins and related thiol reactive molecules downregulate the activity of H2O2-detoxifying enzymes, and thereby allow a transient oxidative burst that triggers the expression of H2O2 responsive genes. It has been shown recently that upon light stress, catalase activity was reversibly inhibited in Chlamydomonas reinhardtii in correlation with a transient increase in the level of H2O2. Here, it is shown that Arabidopsis thaliana mutants lacking the NADP–malate dehydrogenase have lost the reversible inactivation of catalase activity and the increase in H2O2 levels when exposed to high light. The mutants were slightly affected in growth and accumulated higher levels of NADPH in the chloroplast than the wild-type. We propose that the malate valve plays an essential role in the regulation of catalase activity and the accumulation of a H2O2 signal by transmitting the redox state of the chloroplast to other cell compartments.  相似文献   

19.
The heterodimeric [NiFe] hydrogenase from Desulfovibrio fructosovorans catalyzes the reversible oxidation of H2 into protons and electrons. The catalytic intermediates have been attributed to forms of the active site (NiSI, NiR, and NiC) detected using spectroscopic methods under potentiometric but non-catalytic conditions. Here, we produced variants by replacing the conserved Thr-18 residue in the small subunit with Ser, Val, Gln, Gly, or Asp, and we analyzed the effects of these mutations on the kinetic (H2 oxidation, H2 production, and H/D exchange), spectroscopic (IR, EPR), and structural properties of the enzyme. The mutations disrupt the H-bond network in the crystals and have a strong effect on H2 oxidation and H2 production turnover rates. However, the absence of correlation between activity and rate of H/D exchange in the series of variants suggests that the alcoholic group of Thr-18 is not necessarily a proton relay. Instead, the correlation between H2 oxidation and production activity and the detection of the NiC species in reduced samples confirms that NiC is a catalytic intermediate and suggests that Thr-18 is important to stabilize the local protein structure of the active site ensuring fast NiSI-NiC-NiR interconversions during H2 oxidation/production.  相似文献   

20.
An insight into the conformation and dynamics of unfolded and early intermediate states of a protein is essential to understand the mechanism of its aggregation and to design potent inhibitor molecules. Fluorescence correlation spectroscopy has been used to study the effects of several model protein stabilizers on the conformation of the unfolded state and early folding dynamics of tetramethyl rhodamine-labeled cytochrome c from Saccharomyces cerevisiae at single molecular resolution. Special attention has been given to arginine, which is a widely used stabilizer for improving refolding yield of different proteins. The value of the hydrodynamic radius (rH) obtained by analyzing the intensity fluctuations of the diffusing molecules has been found to increase in a two-state manner as the protein is unfolded by urea. The results further show that the presence of arginine and other protein stabilizers favors a relatively structured conformation of the unfolded states (rH of 29 Å) over an extended one (rH of 40 Å), which forms in their absence. Also, the time constant of a kinetic component (τR) of about 30 μs has been observed by analyzing the correlation functions, which represents formation of a collapsed state. This time constant varies with urea concentration representing an inverted Chevron plot that shows a roll-over and behavior in the absence of arginine. To the best of our knowledge, this is one of the first applications of fluorescence correlation spectroscopy to study direct folding kinetics of a protein.  相似文献   

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