A DIURNAL RHYTHM IN THE RATE OF LIGHT-INDUCED ELECTRON FLOW IN MAIZE BUNDLE SHEATH STRIPS

Abstract— A technique for the rapid mechanical isolation of bundle sheath strips from Zea mays was used to study the rate of light-induced electron flow as a function of time of day. Seedlings were raised for 10 days in light/dark cycles and then exposed to various intensities of light. The rate of light-induced electron flow was measured five times during the 24-h cycle using a whole cell, H₂O to methyl viologen assay in the presence of gramicidin. The uncoupled rate of electron flow reached a maximum at midday and then decreased for the remainder of the cycle.
If at the end of the 14-h dark period plants were either maintained in darkness, or exposed to very low irradiance white light. then no rhythmicity was observed. If continuous light at higher irradiance was used, then only one additional peak of activity was observed. The minimal light irradiance necessary to allow the continued expression of the rhythm in light/dark cycles is in the range between 11 to 54 W m_-2. A 15-min bright-light (54 W m_-2) pulse administered at dawn is not sufficient to stimulate the expression of the rhythm indicating that the light during the light/dark cycle is doing more than just acting as a "light-on" synchronizing signal. An imposed dark period is also necessary if the rhythm is to be expressed for more than one cycle.     

ACTION SPECTRUM FOR THE PHOTOPERIODIC INDUCTION OF BULB FORMATION IN Allium cepa L.

Abstract— The action spectrum for the induction of bulb formation in Allium cepa L. was determined by continuous irradiation with monochromatic light for 3 h in the middle of the daily light period of the inductive photoperiod (18 h). The resultant action spectrum showed a single peak at 714 nm. Daily 3 h dark interruptions in the middle of inductive long photoperiods do not permit bulb formation. Bulb formation was inhibited also by monochromatic far red light (758 nm) applied at the beginning of the 3 h dark interruptions. The results of dichromatic irradiations indicate that phytochrome is the only photoreceptor involved in the photoperiodic regulation of bulbing in onion plants. The effect of far red light exhibits the characteristics (action spectrum and fluence rate dependency) of a classical "HIR" response.     

ON THE PHOTOCHEMISTRY OF THE DINUCLEOTIDE TpC*

Abstract— In an aqueous buffered solution of TpC monochromatic ultraviolet light lowers the absorption peak to approximately half its value, characterized by a photostationary state. The quantum yield for this photochemical decomposition is independent of the wavelength between 2400 and 3000 Å.At pH 7 the quantum yield amounts to 0.006, at pH 2 to 0.002, respectively. At neutral pH about 85 per cent of the photochemical transformation produced are reversible in the dark, at pH 2 only 40 per cent. Three photoproducts, being non-reversible in the dark, were isolated electrophoretically and characterized by their absorption spectra. These three compounds have an absorption peak around 2680 Å, one compound has a second absorption maximum at 3120 Å (pH 7).     

SPECIFIC PROTEIN OCCURRENCE RELATED WITH PHOTOPERIODIC FLOWER INDUCTION IN THE COTYLEDONS OF Pharbitis nil CV. VIOLET

In our experiment, three groups of seedlings of SDP Pharbitis nil cv. violet were sepa-rately treated with three different photoperiods (1,16 h dark period--SD; 2, continuous illumi-nation--CL; 3, 16 h dark treatment with 10 min white light in the middle of the dark period--NB). By analysing proteins in the cotyledons from three groups with 2-D PAGE, we found nodifference in protein pattern between the three groups at 0 or 8 h after photoperiodic treatments.At 24 h after the treatments, a specific protein(MW:19 kD; pI: 4.5)appeared only in the cotyledonsof the seedlings which endured SD. This protein disappeared at 72 h after SD. ActinomycinD could inhibit flowering and the specific protein occurrence when applied to cotyledonsprior to SD, but it had no inhibition effect on flowering as well as the specific proteinoccurrence when applied to cotyledons after SD. Chloroamphenicol, a protein synthesisinhibitor, inhibited flowering when applied to cotyledons prior to or immediately after SD,but it did not i     

RHODOPSIN REGENERATION, CALCIUM, AND THE CONTROL OF THE DARK CURRENT IN VERTEBRATE RODS

Abstract— The dark current of retinal rods is suppressed for an extended period when their rhodopsin is bleached. An 8% bleach completely suppresses the current for 8 min and after 35 min it is fully recovered. The dark current can recover fully from a bleaching flash without any rhodopsin being regenerated. Moreover the recovery can be hastened either by lowering the activity of calcium ions surrounding the rods or by regenerating the rhodopsin. The recovery of the dark current following these bleaches showed zero order kinetics, regardless of whether the recovery was hastened by low calcium, 11- cis retinaldehyde or not. If all the rhodopsin is bleached in the retina, the dark current does not recover; the addition of 11- cis retinaldehyde, but not all- trans retinaldehyde, to the bleached retina causes the dark current to begin its recovery as early as 10 min after the addition with zero order kinetics (1.3% min^-1). In two of three similar experiments, the dark current recovered 100%. When the recovery rate of the dark current from the retina showing the earliest response is compared with the rate of the regeneration of rhodopsin in the plasma and disc membranes, the dark current begins its recovery after the plasma membrane rhodopsin is fully regenerated and the disc rhodopsin is half regenerated. When the disc rhodopsin is fully regenerated, the dark current is recovered 75%, and 20 min later it is completely recovered.     

聚丙烯酸甲酯及其模型化合物与O2的初始暗氧化反应

烯酸甲酯及其模型化合物２－甲丁酸甲酯与Ｏ２能够形成不稳定的接触电荷转移复合物。在无光照条件下，通Ｏ２放置一段时间以后再通Ｎ２，ＣＣＴ吸收峰不再完全消失，其残留峰的强度随存放时间的延长，温度的升高而增加，而形和峰位与原ＣＣＴ相似。     

The Quenched Instationary Polymerization System, 3. Derivation of the Radical and Polymer Chain Length Distributions for Any Combination of Two Periods Differing in Initiation Characteristics

The radical and polymer chain length distributions and their respective convolutes were calculated for any combination of an initiation period followed by a dark period without any initiation. The distributions are characterized by the appearance of an asymmetric (broad) additional peak. The choice of the experimental parameters (i. e. duration of the initiation and the dark period) influences the location of the peak as well as the extension of the complete distribution curve. The first and second derivatives also show a characteristic pattern in the region of the peak. A single experiment yields at least two k_p-values which are determined from different parts of the distribution. These values have to be identical unless k_p is not characterized by a single value. In principle, a single experiment will suffice to display possible irregularities in k_p-constancy.     

Circadian gating of photoinduction of commitment to cell-cycle transitions in relation to photoperiodic control of cell reproduction in Euglena

A novel type of circadian and photoperiodic control of the cell division cycle was found in photoautotrophic Euglena gracilis. When algae entrained to 24 h light-dark (LD) cycles (14 h L) were transferred to continuous darkness (DD) at the eighth hour of the final LD photoperiod, cell-cycle transition was arrested in phase G1, S or G2. The subsequent exposure of these dark-arrested cells to a 6 h light-break allowed the dark-arrested cells to undergo cell-cycle progression in DD, in a manner dependent on the circadian phase; maximum photoinduction occurred around dusk. Inhibitor experiments suggested that the photoinduced commitment of G2 cells to cell division required light for a signal originating in noncyclic photosynthetic electron transport (PET), particularly cytochrome b6-f but not for the metabolic energy required by the process. The fact that the circadian rhythm of photoinduction ran out-of-phase from that of noncyclic PET signaling suggests that the site of regulation by the former rhythm is downstream of noncyclic PET. The occurrence of maximum photoinduction around dusk suggests that the 'external coincidence' model of photoperiodic induction describes the activation of the photoinductive phase. Further evidence supporting this hypothesis is the relationship between cell reproduction and day length; the resulting sigmoidal curve indicates a combined effect of photosynthesizing period and circadian stimulation around dusk. Circadian control is shown to be an integral part of the mechanism for 24 h LD cycle-induced synchronous cell division.     

DC photoelectric signals from bacteriorhodopsin adsorbed on lipid monolayers and thiol/lipid bilayers supported by mercury

Purple membrane (PM) fragments were adsorbed on a dioleoylphosphatidylcholine (DOPC) monolayer and on a mixed alkanethiol/DOPC bilayer supported by mercury to investigate the kinetics of light-driven proton transport by bacteriorhodopsin (bR). The light-on and light-off capacitive currents on an alkanethiol/DOPC bilayer at pH 6.4 were interpreted on the basis of a simple equivalent circuit. The pH dependence of the biphasic decay kinetics of the light-on currents was analyzed to estimate the pK(a) values for the transitions releasing protons to, and taking up protons from, the solution. The linear dependence of the stationary light-on current of bR on a DOPC monolayer self-assembled on mercury upon the applied potential was interpreted on the basis of an equivalent circuit.     

Photoelectric response of purple membrane fragments adsorbed on a lipid monolayer supported by mercury and characterization of the resulting interphase

Purple membrane (PM) fragments were adsorbed on a dioleoylphosphatidylcholine (DOPC) monolayer supported by mercury to investigate the kinetics of light-driven proton transport by bacteriorhodopsin (bR). PM fragments were also adsorbed on a mercury-supported triethyleneoxythiol (TET) monolayer. On both monolayers, the light-on current exhibits a finite, potential dependent stationary component that decreases linearly with a positive shift in the applied potential. The light-on and light-off capacitive photocurrents were interpreted on the basis of a simple equivalent circuit, which accounts for the potential dependence of the stationary light-on current. The potential of zero stationary current is about equal to +0.010 V vs. saturated calomel electrode (SCE) on DOPC-coated mercury. The absolute potential difference across the PM fragments adsorbed at this applied potential was estimated on the basis of extrathermodynamic considerations and amounts to about +260 mV; it compares favorably with the value, +250 mV, of the transmembrane potential of zero stationary current across an oocyte plasma membrane incorporating bR [Biophys. J. 74 (1998) 403.]. The effect of the proton pumping activity of photoexcited PM fragments on the electroreduction kinetics of ubiquinone-10 incorporated in the DOPC monolayer underlying the PM fragments was investigated.     

聚苯乙烯的暗氧化及其反应机理研究

聚苯乙烯的暗氧化及其反应机理研究朱军民曹维孝冯新德（北京大学高分子科学与工程系北京１００８７１）关键词聚苯乙烯，异丙苯，接触电荷转移复合物（ＣＣＴ），暗氧化反应高分子材料在加工、贮存和使用的过程中，当受到大气中氧、光、热等作用时，会发生降解和交...     

THE PHOTOPERIODIC CONTROL OF FLOWERING: PROGRESS TOWARD UNDERSTANDING THE MECHANISM OF INDUCTION

The mechanism of photoperiodic flower induction remains a major unsolved problem in plant development. Although it is firmly established that phytochrome is the primary photoreceptor in photoperiodic responses including flowering, the intermediate processes of induction including signal transduction, biochemistry of the induced state, and synthesis and identification of the floral stimulus are still obscure. In this review, advances in key areas of research that have contributed to our understanding of photoperiodic flower induction are discussed. These include the role of phytochrome in photoperiodic flowering, physiological characterization of the photoperiodic flowering response, the mechanism of photoperiodic time measurement during induction, and the nature of flower-promoting and flower-inhibiting substances. Finally, the role of alterations in gene expression in mediating photoperiodic flower induction is considered along with emerging opportunities for future research that may increase our understanding of the mechanism of flower induction.     

TIME-DEPENDENT EFFECTIVENESS OF FAR-RED LIGHT ON THE PHOTOPERIODIC INDUCTION OF BULB FORMATION IN Allium cepa L.

Abstract. The photoperiodic induction of bulbing in onion ( Allium cepa L.) by long daylengths has an absolute requirement for far-red energy during the light period. Far-red light promotes bulbing most effectively during the middle portion of an 18-h inductive photoperiod, requiring about 5 times as much energy for the same response at the beginning and end of this photoperiod. The most effective wavelength for this promotion is 714 nm, suggesting that it is mediated through the high irradiance response (HIR) of phytochrome.     

EFFECT OF CONTINUOUS FAR-RED PREIRRADIATION ON THE LAG PHASE OF CHLOROPHYLL A ACCUMULATION IN PHARBITIS NIL COTYLEDONS

In Pharbitis nil cotyledons, the lag phase of chlorophyll a (Chi a) accumulation which continues for about 2 h after the onset of continuous white light is eliminated by preirradiation with far-red light (FR) for 24 or 48 h. When the period of FR preirradiation is prolonged to 72 h or more, however, the lag phase is observed again (FR-induced lag phase) and the rate of Chi a accumulation during the rapid accumulation phase is lowered below the dark control level.
The application of exogenous 5-aminolevulinate (J-ALA) completely eliminates the FR-induced lag phase, but this treatment eliminates the normal lag phase in dark-grown cotyledons only partially (i.e. Chi a is accumulated but only slowly during the first few h). Application of a 5-ALA precursor, such as glycin + succinate. 2-ketoglutarate or glutamate, eliminates neither the FR-induced lag phase nor the normal lag phase.
A 24- or 48-h FR irradiation seems not only to enable the synthesis of 5-ALA but also to make the other regulatory factors favourable for Chi accumulation. When the period of FR irradiation is prolonged to 72 h or more, the ability to synthesize 5-ALA may be lost.     

EXTRARETINAL PHOTORECEFTION IN INSECTS

Abstract— Extraretinal photoreceptors are widespread among insects and function in the photoperiodic control of development and in the entrainment of circadian rhythms. The effects of light on the daily and seasonal regulation of brain neuroendocrine activity are mediated solely through extraretinal photoreceptors. In primitive insects, the eyes participate in the entrainment of nonendocrine circadian rhythms such as the locomotor rhythm. In more advanced forms, however, extraretinal pathways appear to be the only pathway for the entrainment of all rhythms thus far examined. But even in this latter case, the eyes sometimes effect a masking of the expression of the overt rhythm. An exact localization of the extraretinal receptors has not been accomplished, but in all studies to date they appear to be associated with the cerebral lobe region of the brain. Action spectra for photoperiodic responses have been determined for a number of insects. In general the responses are maximally sensitive in the blue with a marked decline in the red although exceptions do exist. Complete action spectra for circadian responses have been determined only for two insects. In both cases a plateau of sensitivity extends through the blue with a steep drop at longer wavelengths. From the action spectra data, the extraretinal receptors appear to have a threshold sensitivity less than 3 times 10^-2 J/m². The pigment nature of the receptor is unknown although it appears not to be a carotenoid derivative.     

PROTECTION BY THE FLUORIDE ION AGAINST PHTHALOCYANINE-INDUCED PHOTODYNAMIC KILLING OF CHINESE HAMSTER CELLS

When a dilute F- solution was added to a culture of Chinese hamster cells that had been preincubated with an aluminium phthalocyanine sensitizer derived from AlPcCl, the photosensitivity of the cells was markedly reduced compared to control cells not treated with F-. Under the same treatment conditions, the reduction in [3H]thymidine incorporation into cellular DNA caused by light and this sensitizer and the production of DNA-protein crosslinks caused by light and this sensitizer were also inhibited by F-. In contrast, the killing of Chinese hamster cells, the reduction of thymidine incorporation by the cells, and the production of DNA-protein crosslinks in the cells caused by the combination of light and either Photofrin II or the silicon phthalocyanine HOSiPcOSi(CH3)2(CH2)3-N(CH3)2 were not inhibited by F-. We conclude that the aluminium phthalocyanine sensitizer used is largely or completely AlPc(OH)(H2O), that it is converted to a fluoro complex by F-, and that this compound probably is a less efficient generator of photochemical damage at a critical cellular target(s) than is AlPc(OH)(H2O). The inhibition of thymidine incorporation and DNA-protein crosslink formation indicates that the effects of F- can be expressed at intracellular sites. It is further concluded that the silicon phthalocyanine sensitizer and Photofrin II do not interact significantly with F-.     

ALUMINUM SULFONATED PHTHALOCYANINE DISTRIBUTION IN RODENT TUMORS OF THE COLON, BRAIN and PANCREAS

Abstract The most widely discussed aspect of photodynamic therapy (PDT) is the preferential uptake and retention of sensitisers by malignant tissues. The sensitiser usually used is hematoporphyrin derivative (HPD) but this compound is not an ideal photosensitiser for this purpose and we have therefore studied an aluminum sulfonated phthalocyanine (AlSPc) as a possible alternative. Here we have studied the uptake and retention of this compound in a rat colon cancer, a hamster pancreatic cancer and a mouse glioma, using an alkali extraction technique to estimate tissue AlSPc and comparing the results with those from the corresponding normal tissues. All of the tumors studied reached accumulation peaks at 24-48 h after intravenous administration of AlSPc compared with peaks at 1-3 h in the normal tissues. The tumors outside the central nervous system (CNS) reached peak tumor : normal tissue ratios of 2-3 : 1 and the tumor within the CNS, the malignant glioma, reached a far higher ratio of 28 : 1. These ratios are similar to those reported by others using HPD.     

GENETIC AND PHYSIOLOGICAL STUDIES OF THE EFFECT OF LIGHT ON THE DEVELOPMENT OF THE MOSS, PHYSCOMITRELLA PATENS

The germination of Physcomitrella patens spores only occurs when wet spores are exposed to light. Depending on their ripeness, spores require from 44 to 64 h illumination to bring about maximum germination. There is a lag period of about 15 h between the reception of sufficient light to elicit germination before germination can be observed. Wavelengths in the range 640–64080 nm are much more effective in inducing germination than longer or shorter wavelengths, but far-red reversal of red light induction of germination has not been demonstrated. Light also has very marked effects on protonemal and gametophore development. In darkness, only caulonemata are produced, and these grow negatively geotropically. No new gametophores develop but existing gametophores grow negatively geotropically, etiolate and bear only scale leaves. In light, chloronemata, as well as caulonemata are produced, the former grow positively phototropically, while the latter grow at right angles to the direction of light, and neither cell type is sensitive to gravity. In the light, gametophores grow positively phototropically, are indifferent to gravity, produce large leaves and do not etiolate. All these responses to light by protonemata and gametophores are shown by cultures growing in a 23 h dark/l h red light cycle, but if this red light treatment is followed by 15min far-red light, the effect of the red light is reversed, indicating an involvement of phytochrome in the mediation of these responses. Mutants showing abnormal growth in the dark have been isolated, as well as mutants having abnormal phototropic responses. The latter type has lost the phototropic response of both the protonemal cell types, as well as of gametophores, indicating that these different responses may share a common component.     

Interference of the electrospray voltage on chromatographic separations using porous graphitic carbon columns

The electrospray ionization (ESI) voltage is shown to interfere with liquid chromatographic separations performed with packed porous graphitic carbon (PGC) capillary columns. This interference is ascribed to the presence of an electric field over the conductive column in the absence of an earth point between the column and the ESI emitter. The current evolved alters the chromatographic behavior of the catecholamine metabolite 3-O-methyl-DOPA significantly, as both peak splitting and a dramatic decrease in the retention time were observed. Furthermore, the response from the mass spectrometer was decreased by 33% at the same time. A related compound, tyrosine, exhibited decreased retention times but no peak splitting, whereas no shifts in the retention times (or peak splitting) were seen for the less retained dopamine and noradrenaline. When the current through the PGC column was eliminated by the use of an earth point between the column and the ESI emitter, the chromatographic behavior of the column was found to return slowly to normal after hours of equilibration with 60 : 40 (v/v) methanol-ammonium formate buffer of pH 2.9. The behavior of the PGC column with and without the earth point was found to be highly reproducible during a period of 1 month. We propose that the effect of the ESI voltage on the chromatographic behavior of the PGC column is due to associated redox reactions affecting both the PGC particles and the analytes. It is concluded that (for analytical reasons), care should be taken to ensure that no current is flowing through the chromatographic system when interfacing PGC columns, and conducting parts in general, to ESI mass spectrometry.     

两种不同光谱类型的R-藻红蛋白的荧光性质研究

红藻中的R-藻红蛋白(R-PE)依照其吸收光谱可分为两种不同的光谱类型,即“双峰型”和“三峰型”。本文通过对不同pH条件下的R-PE的荧光光谱及荧光寿命的研究,发现“三峰型”R-PE的pH稳定范围较“双峰型”R-PE大。在R-PE浓度对荧光光谱的影响实验中,随着蛋白浓度的增加,荧光峰位置逐渐红移。荧光寿命逐渐增大,荧光强度先行增加而后减弱。用碘离子对其荧光进行猝灭,随着碘离子浓度的增大,荧光强度逐渐降低,荧光寿命逐渐缩短,并服从Stem-Volmer规则。