Anisotropy decay of fluorescence as an experimental approach to protein dynamics

This minireview makes an initial assessment of the progress made using anisotropy decay measurements for investigating the conformational changes and molecular dynamics in soluble systems. A critical analysis of available data is presented. The anisotropy decays of the tryptophan fluorescence of staphylococcal nuclease, adrenocorticotropin, melittin and of labeled transfer RNA were studied for investigating the functional conformational changes of these systems. The emissions of variously labeled immunoglobulins have been used to elucidate the conformations of these proteins before and after the binding of specific antibodies. Labeled myosin and its fragments have given information on the functional motions of the protein domains. The anisotropy decays of labeled and natural hemoglobin systems have been utilized for exploring the allosteric behavior of these molecules. The data suggest a wide applicability of this technique to the study of protein dynamics and conformational changes of macromolecules.     

Synchrotron-excited time-resolved fluorescence spectroscopy of adenosine,protonated adenosine and 6N, 6N-dimethyladenosine in aqueous solution at room temperature

The fluorescence behavior of adenosine in neutral solution has been studied by time-resolved spectroscopy using synchrotron excitation and timecorrelated single photon counting, and by decay time measurements. Three emissions have been identified and correlated with three excitation spectra. The assignment of these transitions has been made by comparison with similar measurements on ⁶N, ⁶N-dimethyladenosine (6 DMA), and on adenosine in acid solution (ADO H⁺). It is proposed that two of the transitions of adenosine which correlate with 6DMA originate from coplanar and orthogonal rotational conformers of the amino group. The other transition, correlating with ADO H⁺ may originate either from the ³H-imino tautomer, or from a differently solvated rotational conformer.A partial presentation of this work has been made at the Second Congress of the European Society for Photobiology Padova, Italy, 6–10 September 1987     

Morphology and ontogeny of stem xylem elements inSarcandra glabra (Thunb.) Nakai (Chloranthaceae): Additional evidence for the occurrence of vessels

Very recentlySarcandra, which had long been known as the only vesselless genus in Chloranthaceae, was found by Carlquist to have vessels in root secondary xylem. The present study further shows on the basis of observations of the xylem ontogeny that vessels occur in stem metaxylem ofSarcandra glabra as well, thus offering additional evidence for the occurrence of vessels in the genus, virtually in all Chloranthaceae. Metaxylem elements of the stem are thicker than the other tracheary elements in general and have scalariform pittings at the end wall, and their ontogeny indicates that, as the surrounding cytoplasm disintegrates, pit membranes at the end wall disappear at least in some elements, resulting in a perforated end wall, i.e., vessel perforation. The present study further shows thatChloranthus spicatus, which is closely related toSarcandra, may have an incomplete perforation plate because of retaining membranes at places on the plate. An evolutionary state of the “vesselless” condition in Chloranthaceae is discussed.     

Population density ofMonochamus alternatus adults (Coleoptera: Cerambycidae) and incidence of pine wilt disease caused byBursaphelenchus xylophilus (Nematoda: Aphelenchoididae)

Summary The seasonal occurrence ofMonochamus alternatus and newly weakened trees were investigated in aPinus thunbergii stand for 4 years. Adult beetles were present between June and September with a peak in their population occurring in early July followed by a decline then a period of about one month being in a steady number. The average number ofBursaphelenchus xylophilus (Nematoda), which is the causal agent of pine wilt disease, within beetles decreased as the season advanced. Pine trees newly weakened byB. xylophilus appeared between June and October, especially from August to October. The proportion of weakened or killed trees was directly proportional to the average beetle density per tree from June to August.     

An inflatable minirhizotron system for root observations with improved soil/tube contact

Commonly used minirhizotrons consisting of a transparent tube inserted into the soil seldom attain good contact between the tube and the soil, which leads to root growth occurring in a gap rather than in the soil. A new system is described involving an inflatable flexible rubber wall, made from a modified motorcycle tube. Pressure ensures a proper tube/soil contact so that the environmental circumstances for root growth along the tube more closely correspond to those in the undisturbed soil. Before the endoscope slide is introduced into the minirhizotron for taking pictures, the inflatable tube is removed, so that there is no-often opaque-wall between the endoscope and the roots. This improves the picture quality and facilitates the analysis of root images.     

Fluorescence decay of pyrene in small and large unilamellar L,α-Dipalmitoylphosphatidylcholine vesicles above and below the phase transition temperature

The fluorescence decays of pyrene in small and large unilamellar L,-dipalmitoylphosphatidylcholine vesicles have been investigated as a function of probe concentration and temperature. When the molar ratio of pyrene to phospholipid equals 1:3000, no excimer emission is observed and the fluorescence decays are mono-exponential. When this ratio is equal to or higher than 1:120, excimer formation is observed.Above the phase transition temperature the observed fluorescence decays of monomer and excimer can be adequately described by a bi-exponential function. The monomer decays can be equally well fitted to a decay law which takes into account a time-dependence in the probe diffusion rate constant. The fluorescence decay kinetics are compatible with the excimer formation scheme which is valid in an isotropic medium. The excimer lifetime and the (apparent) rate constant of excimer formation have been determined as a function of probe concentration at different temperatures above the phase transition temperature. The activation energy of excimer formation is found to be 29.4±1.3 kJ/mol. In small unilamellar vesicles the diffusion constant associated with the pyrene excimer formation process varies from 8.0x10^-7 cm²/s at 40°C to 2.2x10^-6 cm²/s at 70°C.Below the phase transition temperature the monomer decays can be described by a decay law which takes into account a time dependence of the rate constant of excimer formation. The lateral diffusion coefficient of pyrene calculated from the decay fitting parameters of the monomer region varies from 4.0x10^-9 cm²/s at 20°C to 7.9x10^-8 cm²/s at 35°C. No significant difference could be observed between the pyrene fluorescence decay kinetics in small and large unilamellar vesicles.Abbreviations SUV small unilamellar vesicles - LUV large unilamellar vesicles - DPPC dipalmitoylphosphatidylcholine - DMPC dimyristoylphosphatidylcholine - FRAP fluorescence recovery after photobleaching Part of this research has been presented at the 5th international symposium on surfactants in solution. Bordeaux, July 9th–13th 1984     

图们江流域林区居民点鸟类群落的研究

居民点鸟类与人类关系极为密切,在居民点生态系统中起着不可忽视的作用,因此对其生态学的研究具有一定意义。杜恒勤(1958、1959)、周昌乔等(1959)、钱国桢(1964)、郑光美(1965、1982),赵正阶(1981)等,对麻雀、家燕、金腰燕等居民点鸟类进行过大量种群生态学研究。居民点鸟类群落研究和数量统计,尚未见有报道。     

Root growth dynamics of Brussels sprouts (Brassica olearacea var.gemmifera) and leeks (Allium porrum L.) as reflected by root length,root colour and UV fluorescence

Minirhizotron observations of roots of leeks and Brussels sprouts grown in the Wageningen Rhizolab were used to study the dynamics of root length. Day of appearance and the time of decay were assessed for individual root segments visible on the minirhizotron surface.A Brussels sprouts crop produced much more root length than leeks, but the average longevity of these roots was about half that of leek roots.To investigate whether root colour or UV fluorescence could be used as a quantitative index of root functionality or root age, changes in root colour (on a scale of greys) over time were measured with interactive image analysis. In both crops a gradual change towards black was found with ageing. Measurements of the intensity of the UV fluorescence showed that leek roots fluoresced more than Brussels sprouts roots. Over time, UV fluorescence decreased in Brussels sprouts roots but increased in leek roots. It is concluded that UV fluorescence cannot be used as a universal indicator of root age or root functionality, but in some plant species it may be used to separate (transparent) roots from the background with image analysis techniques.