Appearance of a State 1 – State 2 transition during chloroplast development in the wheat leaf: Energetic and structural considerations

The ability of developing chloroplasts to dynamically regulate the distribution of excitation energy between photosystem 1 and photosystem 2, and thus perform a State 1 – State 2 transition, was examined from analyses of chlorophyll fluorescence kinetics in 4- and 8-day-old Triticum aestivum L. cv. Maris Dove leaves grown under a diurnal light regime. Chloroplasts at all stages of development in the two leaf systems could undergo a State 1 – State 2 transition, except those found in the basal 0.5 cm of the 4-day-old leaf. The ability to physiologically modify the excitation energy distribution between the chlorophyll matrices of the two photosystems developed after the development of mature, fully photochemically competent photosystem 2 units and the appearance of excitation energy transfer between photosystem 2 and photosystem 1. Also, changes in the degree of energetic interaction between the two photosystems, in vivo rates of electron transport and the chlorophyll a/b ratio could not be correlated with the appearance of a State 1 – State 2 transition. Ultrastructural studies demonstrated a 32% increase in the degree of thylakoid appression in chloroplasts at the base of the 8-day-old leaf compared to the situation in the basal 0.5 cm of the 4-day-old leaf. This difference in thylakoid stacking can account for the differing abilities of these two tissues to perform a State 1 – State 2 transition when considered in the context of the distribution of the two photosystems within appressed and non-appressed regions of thylakoid membranes.     

猫初级视皮层内GIu/GABA表达比率的衰老性变化

最近的一些研究结果显示,视皮层内抑制性递质系统作用减弱可能是导致老年性视觉功能衰退的重要因素.是否皮层内兴奋性递质系统亦伴随衰老而发牛改变并影响皮层内神经兴奋与抑制的平衡尚不清楚.为此,利用Nissl染色和免疫组织化学染色方法以及Image-Pro Express图像分析软件对青、老年猫初级视皮层(17区)内各层神经元密度、兴奋性递质谷氨酸免疫反应阳性(Glu-immunoreactive,Glu-IR)神经元密度以及抑制性递质γ-氨基丁酸免疫反应阳性(γ-aminobutyric acid.immunoreactive,GABA-IR)神经元密度进行了统汁分析.结果显示,青、老年猫初级视皮层各层神经元密度均没有明显的年龄性差异(P>0.05);与青年猫相比,老年猫初级视皮层Glu-IR、GABA-IR神经元密度均显著减少(P<0.01),而Glu.IR/GABA.IR神经元密度比率去却显著增大(P<0.01).结果提示,老年猫初级视皮层内兴奋性递质系统作用相对增强,而抑制性递质系统的作用相对减弱,导致皮层内兴奋-抑制平衡关系失调,这可能是引起老年个体视觉功能衰退的重要原因之一.     

自身代谢缓解甲氨蝶呤对小鼠体内成熟卵母细胞副作用的研究

甲氨蝶呤(methotrexate,MTX)作为抗叶酸代谢类药物,在临床上应用广泛.其副作用之一表现为损伤卵母细胞质量.那么,对于有妊娠需求的女性服药者,停药后多久才适合受孕呢?该文结合双光子荧光成像与三维重构技术研究此问题.通过单次腹腔注射生理盐水及5 mg/kg MTX建立了对照组和MTX组小鼠,随后建立了MTX注...     

Circulation of excitation waves in a model medium containing unexcitable obstacles

Serial semithin optical sections were used for 3D reconstruction of rat ventricular tissue. At histological resolution, older animals (18 months) were found to have regions of fibrous connective tissue not observed in young animals (2 months). The 3D data were used in mathematical modeling of excitation wave propagation in a medium containing such obstacles. The values of conductance, medium excitation threshold, and pulse repetition rate were determined whereat the model predicts rhythm disorders caused by circulation of the excitation wave.     

Energy migration in purple bacteria. The criterion for discrimination between migration- and trapping-limited photosynthetic units

A criterion has been evolved for distinguishing between migration- and trapping-limited photosynthetic units (PSUs). Its application to purple bacteria has proved their PSUs to be of trapping-limited type. It means that any improvements of the molecular structure of their PSUs cannot noticeably increase the overall rate constant of excitation delivery from antenna BChls to reaction centers (RCs).Abbreviations PSUs photosynthetic units - RCs reaction centers - Chl chlorophyll - BChl bacteriochlorophyll - R intermolecular distance, _e - quantum yields of the primary excitation trapping and wasteful losses respectively - _fl excitation and fluorescence lifetimes respectively     

Supramolecular zippers elicit interbilayer adhesion of membranes producing cell death

Background

The fluorescent dye 10-N-nonyl acridine orange (NAO) is widely used as a mitochondrial marker. NAO was reported to have cytotoxic effects in cultured eukaryotic cells when incubated at high concentrations. Although the biochemical response of NAO-induced toxicity has been well identified, the underlying molecular mechanism has not yet been explored in detail.

Inhomogeneous Encoding of the Visual Field in the Mouse Retina

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Dynamic Remodeling of Pericytes In Vivo Maintains Capillary Coverage in the Adult Mouse Brain

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Overdrive excitation in the guinea pig sinoatrial node superfused in high [K+]o

The aim of the present experiments was to study the characteristics and mechanisms of the rhythm induced by overdrive (overdrive excitation, ODE) in the sinoatrial node (SAN) superfused in high [K⁺]_o (8–14 mM). It was found that: (1) overdrive may induce excitation in quiescent SAN and during a slow drive; (2) in spontaneously active SAN, overdrive may accelerate the spontaneous discharge; (3) immediately after the end of overdrive, a pause generally precedes the onset of the induced rhythm; (4) during the pause, an oscillatory potential (V_os) may be superimposed on the early diastolic depolarization (DD); (5) during the subsequent late DD, a different kind of oscillatory potential appears near the threshold for the upstroke (ThV_os) which is responsible for the initiation of spontaneous activity; (6) once started, the induced rhythm is fastest soon after overdrive; (7) faster drives induce longer and faster spontaneous rhythms; (8) the induced action potentials are slow responses followed by DD with a superimposed V_os, but ThV_os is responsible for ODE; (9) the induced rhythm subsides when ThV_os miss the threshold and gradually decay; (10) low [Ca²⁺]_o abolishes ODE; (11) in quiescent SAN, high [Ca²⁺]_o induces spontaneous discharge through ThV_os and increases its rate by enhancing V_os and shifting the threshold to more negative values, and (12) tetrodotoxin abolishes ODE as well as the spontaneous discharge induced by high [Ca²⁺]_o. In conclusion, in K⁺-depolarized SAN, ODE may be present in the apparent absence of calcium overload, is Ca²⁺- and Na⁺-dependent and is mediated by ThV_os and not by V_os.     

Suppression of radiation damping during selective excitation of the water signal: The WANTED sequence

Summary A new pulse sequence is presented allowing the use of long selective pulses at the water frequency using standard equipment. Radiation damping is suppressed during the pulse by the use of gradient echoes programmed between the single pulses of a DANTE train. This WANTED (water-selective DANTE using gradients) sequence thus allows the observation of interactions with water without the use of special probe heads or filtering of undesired resonances. By combining the WANTED sequence with NOESY, ROESY and NOESY-GSQC experiments, we obtain selective 1D and 2D spectra fit to the observation of chemical exchange and dipolar interactions between water and protein protons.