Primary photosynthetic processes in Heliobacterium chlorum at 15K

Absorbance changes induced by 25-ps laser flashes were measured in membranes of Heliobacterium chlorum at 15 K. Absorbance difference spectra, measured at various times after the flash showed negative bands in the Q_y region at 812, 793 and 665 nm. The first of these bands was attributed to the formation of excited singlet states of a long-wavelength form of antenna bacteriochlorophyll g (BChl g 808). Absorbance changes of shorter wavelength absorbing antenna BChls g were at least an order of magnitude smaller, indicating rapid excitation energy transfer (i.e. within the time resolution of the apparatus) from these BChls to BChl g 808. Excited BChl g 808 showed a bi-exponential decay with time constants of 50 and 200 ps. The bands at 793 and 665 nm may be attributed to the primary charge separation and reflect the photooxidation of the primary electron donor P-798 and photoreduction of a primary electron acceptor absorbing near 670 nm, presumably a BChl c or Chl a-like pigment. The bleaching of this pigment reversed with a time constant of 300 ps at 15 K and of 800 ps at 300 K. This indicates that electron transfer from the primary to the secondary electron acceptor is approximately 2.5 times faster at 15 K than at room temperature.Abbreviations BChl bacteriochlorophyll - FWHM full width at half maximum - P-798 primary electron donor - Tris tris(hydroxymethyl)amino methane     

Preparation of megabase-sized tomato DNA and separation of large restriction fragments by field inversion gel electrophoresis (FIGE)

The Schwartz and Cantor technique for releasing and fractionating megabase-sized DNA from agarose-embedded cells is beginning to bridge the gap in resoluation between classical genetics and current molecular DNA techniques, particularly in mammalian systems. As yet no conditions have been described for preparing plant DNA that is of sufficient length to allow similar long-range restriction mapping experiments in plant systems. In this report, we describe the application of the Schwartz and Cantor technique for preparing high molecular weight DNA from embedded tomato leaf protoplasts, as well as conditions for generating and fractionating large restriction fragments, by field inversion gel electrophoresis (FIGE). The bulk of DNA released from lysed protoplasts was at least 2 Mb in size and amenable to restriction digestion as shown by hybridizing Southern blots with, among others, a probe for the Adh-2 gene of tomato. Restriction fragments as large as 700 kb were detected. Chloroplast DNA is isolated intact, amenable to restriction analysis and, in its native form, not mobile in FIGE.     

Periodic electric field as a biopolymer conformation switch: a possible mechanism

A theoretical model is proposed to describe the influence of a periodic electric field (PEF) upon a biopolymer. The biopolymer is treated as a classical mechanical system consisting of subsystems (molecular groups) which interact with each other through potential forces. The PEF is treated as a periodic driving force applied to a molecular group. The energy dissipation is considered using the model of fluid (viscous) friction. Arguments for the non-linear character of the friction-velocity dependence caused by the non-Newtonian rheology of a viscous medium are formulated.A forced molecular-group motion is investigated for the situation of a small driving-force period, with oscillations overdamped and a driving force consisting of more than one harmonic. As a result, it is established that the motion always gets to a terminal stage when only a small-scale vibration about some point, X ^*, takes place. The terminal motion is preceded by a transient characterized by the presence of a directional velocity component and so by a drift along a potential profile. the drift goes on until a barrier is met which has a sufficiently large steepness (the barrier height is not important). As a result, the point X ^* may happen to be remote from the conformation potential local minimum (conformational state). The physical reasons for the drift are described.If we consider the small-scale vibration about X ^* in the framework of the hierarchy of scales for intramolecular mobility, it can be regarded as an equilibrium mobility, whereas the drift can be regarded as a functionally important motion, and X ^* as a new conformational state which is realizable only in the presence of the PEF. It may be concluded, as the result of a consistent treatment and neglecting the small-scale vibration, that the conformational potential is modified by adding a linear term (in the one-dimensional case). In this connection, the set of conformational states can both deform (deviation of the positions of minima and their relative depth) and rearrange qualitatively (some minima can vanish and/or new minima can appear). In particular, the transition from one conformation to another one may happen due to rearrangement.     

中国九个人群耵聍的遗传多态性

报道了九个人群的耵聍位点基因。计算表明中国各族人群在耵聍位点上的遗传分化程度非常大,固定指数F_(ST)=0.22。本文根据耵聍基因频率在我国和邻近地区的分布趋势,认为亚洲东北地区应是干型基因的起源地,目前世界上耵聍位点基因频率分布格局主要是基因扩散的结果,而非选择作用造成的。     

Analysis of electric and magnetic fields leaking from induction heaters

Results are presented of an investigation on electric and magnetic fields leaking from inductive (magnetic) heaters that are used for thermal processing of high-power electron tubes and lasers in an industrial plant. Measurements of electric and magnetic fields were done using both commercially available and laboratory-developed instrumentation. Isotropic H-field sensors were developed to allow quantitative evaluation of high-intensity magnetic fields. Ten induction heaters with nominal A.C. power ranging from 2.5 kW to 15 kW and operating at frequencies between 300 kHz and 790 kHz were surveyed. Electric field strengths up to 8 kV/m and magnetic field strengths up to 20 A/m were measured.     

Chronic exposure to ELF fields may induce depression

Exposure to extremely-low-frequency (ELF) electric or magnetic fields has been postulated as a potentially contributing factor in depression. Epidemiologic studies have yielded positive correlations between magnetic- and/or electric-field strengths in local environments and the incidence of depression-related suicide. Chronic exposure to ELF electric or magnetic fields can disrupt normal circadian rhythms in rat pineal serotonin-N-acetyltransferase activity as well as in serotonin and melatonin concentrations. Such disruptions in the circadian rhythmicity of pineal melatonin secretion have been associated with certain depressive disorders in human beings. In the rat, ELF fields may interfere with tonic aspects of neuronal input to the pineal gland, giving rise to what may be termed "functional pinealectomy." If long-term exposure to ELF fields causes pineal dysfunction in human beings as it does in the rat, such dysfunction may contribute to the onset of depression or may exacerbate existing depressive disorders.     

The effects of guanine and cytosine variation on dinucleotide frequency and amino acid composition in the human genome

Summary One hundred twelve human DNA sequences were analyzed with respect to dinucleotide frequency and amino acid composition. The variation in guanine and cytosine (G+C) content revealed: (1) at 2–3 and 3-1 doublet positions CG discrimination is attenuated at high G+C, but TA disfavor is enhanced, and (2) several amino acids are subject to G+C change. These findings have been reported in part for collections of sequences from various species. The present study confirms that in a single organism-the human-the G+C effects do exist. Aspects of the argument that connects G+C with protein thermal stability are also discussed.     

Measurement of Free Intracellular Calcium in the Brain by 19F-Nuclear Magnetic Resonance Spectroscopy

We report the first measurement of the free intracellular calcium level in an actively metabolising intact cerebral tissue preparation. To this end, we applied the recently developed 19F-nuclear magnetic resonance calcium chelator, 5,5'-F2-1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (5FBAPTA), in superfused cerebral cortical slices to give values for the intracellular Ca2+ concentration of 350 and 480 nM, at external calcium concentrations of 1.2 and 2.4 mM, respectively. Under both conditions, the intracellular Ca2+ concentration was increased by depolarisation using a high external K+ concentration. Interleaved 31P spectra showed that the presence of the 5FBAPTA had a deleterious effect on the metabolic state of the tissue with an external Ca2+ concentration of 1.2 mM, but normal viability was maintained using 2.4 mM.     

Combined effect of light and temperature on triacylglycerol accumulation in Dicranum elongatum

In the subarctic moss Dicranum elongatum Schleich & Schwaegr., the level of total lipids and triacylglycerols (TAG) was high in late winter and spring and low in autumn and winter. Four-week exposure of field material to continuous light (135μmol m⁻²s⁻¹) at 1°C resulted in a considerable increase in the amount of TAG in the autumn material acclimated to low temperatures and rhythmic light in the field. In contrast, the same treatment did not cause any increase in TAG in the spring material, acclimated to low temperatures and continuous light in the field. Results from experiments, in which moss cultivated for 4 months at 9°C on 12-h photoperiods (135μmol m⁻²s⁻¹) was kept for 3 weeks at low temperatures (9°C and −3°C) either in continuous light (135 or 70 μmol m⁻²s⁻¹) or with 12-h photoperiods (135 μmol m⁻²s⁻¹), indicated that the TAG level was higher at higher light intensity. At 9°C it was also higher in continuous light of both intensities than in rhythmic light. These results strongly suggest that decreasing irradiance and decreasing daylength limits the accumulation of TAG in D. elongatum during autumn in the subarctic.     

诱导小麦-天兰偃麦草-黑麦三属杂种花粉植株的研究

以法国六倍体小黑麦为母本,分别与普通小麦(Triticum aestivum)和天兰偃麦草(Elytrigia intermedia of Agropyron glaucum)的杂交后代中的中间类型3号和5号杂交。由此获得的三属杂种F_1性状介于亲本之间,兼有三属亲本类型的特征,呈中间类型。用马铃薯-Ⅱ培养基培养三属杂种F_1的花药,诱导花粉愈伤组织。将所获得的愈伤组织转入190-2培养基进行分化,已成功地诱导出一批三属间杂种花粉植株,并用Giemsa显带技术鉴定花粉植株的染色体组组成。