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1.
In this paper, we present the first measurements on thermoluminescence from isolated thylakoids to probe the recombination reactions of S2 (or possibly S3) with Q?B or Q?A, after bicarbonate depletion and its readdition. The effects of bicarbonate depletion on the S2Q?B (or S3O?B) thermoluminescence band was (1) a 6–10°C shift to a higher temperature; (2) a reduction in its intensity upon prolonged depletion; and (3) elimination after the first few flashes of the characteristic period four oscillations in its intensity as a function of the flash number. On the other hand, addition of diuron (3-(3′,4′-dichlorophenyl)-1,1-dimethylurea), which blocks electron flow from Q?A to QB, produced the same thermoluminescence band, at about + 20°C, assigned to S2Q?A recombination, in both depleted and reconstituted samples. These results suggest (1) the initial effect of bicarbonate depletion is to increase the activation energy for S2(S3)Q?B recombination; (2) with further depletion, the incidence of this recombination decreases and the cycling of the S2Q?B and S3Q?B recombination is inhibited through effects at the QB apoprotein; and (3) the depletion effects are fully reversible. It is suggested that a conformational change of the PS II complex in the region of the QB apoprotein is responsible for these effects. 相似文献
2.
Oxygen evolution and reduction kinetics of the photooxidized Chl-aII + have been measured in oxygen-evolving complexes from the thermophilic cyanobacterium Synechococcus sp.
- Incubation of PS II particles with acetate resulted in an inhibition of oxygen evolution and a retardation of the Chl-aII +=reduction kinetics from the nanosecond range to the microsecond range, indicating a modification of the donor side of photosystem II (PS II).
- After the first two flashes given to a dark-adapted, acetate treated sample, Chl-aII + was re-reduced with a half-life time of 160 μs by a component of the donor side of PS II. Under repetitive excitation Chl-aII + was re-reduced in 500 μs by electron back reaction from the primary acceptor QA - (X-320-). Obviously, in the presence of acetate only two electrons are available from the donor side.
- Both oxygen evolution and nanosecond reduction kinetics of Chl-aII + were restored to the control level when acetate was removed.
- The results indicate a tight coupling between O2 evolution and nanosecond reduction kinetics of Chl-aII +.
- The reversible inhibition is probably due to a replacement of Cl- by acetate within the water splitting enzyme.
- Due to its strongly retarded kinetics, the reversibly modified system may facilitate investigations of the mechanism of the donor side.
3.
Thermoluminescence experiments have been carried out to study the effect of a transmembrane proton gradient on the recombination properties of the S2 and S3 states of the oxygen evolving complex with QA
- and QB
-, the reduced electron acceptors of Photosystem II. We first determined the properties of the S2QA
- (Q band), S2QB
- and S3QB
- (B bands) recombinations in the pH range 5.5 to 9.0, using uncoupled thylakoids. The, a proton gradient was created in the dark, using the ATP-hydrolase function of ATPases, in coupled unfrozen thylakoids. A shift towards low temperature of both Q and B bands was observed to increase with the magnitude of the proton gradient measured by the fluorescence quenching of 9-aminoacridine. This downshift was larger for S3QB
- than for S2QB
- and it was suppressed by nigericin, but not by valinomycin. Similar results were obtained when a proton gradient was formed by photosystem I photochemistry. When Photosystem II electron transfer was induced by a flash sequence, the reduction of the plastoquinone pool also contributed to the downshift in the absence of an electron acceptor. In leaves submitted to a flash sequence above 0°C, a downshift was also observed, which was supressed by nigericin infiltration. Thus, thermoluminescence provides direct evidence on the enhancing effect of lumen acidification on the S3S2 and S2S1 reverse-transitions. Both reduction of the plastoquinone pool and lumen acidification induce a shift of the Q and B bands to lower temperature, with a predominance of lumen acidification in non-freezing, moderate light conditions.Abbreviations 9-AA
9-aminoacridine
- EA
activation energy
- F0
constant fluorescence level
- FM
maximum fluorescence, when all PS-II centers are closed
- FV
variable fluorescence (FM–F0)
- PS I, PS II
Photosystem I, photosystem II
- PQ
plastoquinone
- TL
thermoluminescence 相似文献
4.
The effect of desiccation and rehydration on the function of Photosystem II has been studied in the desiccation tolerant lichen Cladonia convoluta by thermoluminescence. We have shown that in functional fully hydrated thalli thermoluminescence signals can be observed from the recombination of the S2(3)QB
– (B band), S2QA
– (Q band), Tyr-D+QA
– (C band) and Tyr-Z+(His+)QA
– (A band) charge stabilization states. These thermoluminescence signals are completely absent in desiccated thalli, but rapidly reappear on rehydration. Flash-induced oscillation in the amplitude of the thermoluminescence band from the S2(3)QB
– recombination shows the usual pattern with maxima after 2 and 6 flashes when rehydration takes place in light. However, after rehydration in complete darkness, there is no thermoluminescence emission after the 1 st flash, and the maxima of the subsequent oscillation are shifted to the 3rd and 7th flashes. It is concluded that desiccation of Cladonia convoluta converts PS II into a nonfunctional state. This state is characterized by the lack of stable charge separation and recombination, as well as by a one-electron reduction of the water-oxidizing complex. Restoration of PS II function during rehydration can proceed both in the light and in darkness. After rehydration in the dark, the first charge separation act is utilized in restoring the usual oxidation state of the water-oxidizing comples.Abbreviations Chl
chlorophyll
- DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- DT
desiccation tolerant
- PS II
Photosystem II
- TL
thermoluminescence
- P680
reaction center Chl of PS II
- QA and QB
puinone electron acceptors of PS II
- S0,...,S4
the redox states of the water-oxidizing complex
- Tyr-Z and Tyr-D
redox-active tyrosine electron donors of PS II 相似文献
5.
Arun K. Agrawal 《Plant Ecology》1990,88(2):177-187
This paper reports the analysis of floristic composition and phenology of protected, annually scraped and fired, and heavily grazed grasslands community of Western Himalaya.
- A total of 19, 20 and 23 species were recorded at protected (S1), annually scraped and fired (S2) and heavily grazed (S3) sites respectively.
- Domination of therophytic flora as indicated by biological spectrum study, was noted in all the three sites.
- Density of plants reached a maximum in the rainy season and amounted to be 4300.5, 3439.8 and 3298.0 tillers/m2 on S1, S2 and S3 respectively.
- Maximum total basal cover was also recorded in the rainy season and amounted to be 769.9, 3390.6 and 2295.7 cm2/m2 on S1, S2 and S3 respectively.
- Correlation between density and basal cover was positive on all three sites.
6.
Energy dependent reverse electron flow reactions in isolated thylakoids provide a unique tool to study, in the dark, the coupling between the ATP synthase, proton transport and the electron transfer system. Appropriate experimental conditions have been established to follow experimentally the following reactions:
- ATP driven proton uptake into the inner-thylakoid space, which requires preactivation of the ATP synthase.
- ATP driven reverse electron transport, which involves proton transport as an intermediate, and results in the reduction of QA by an externally added electron donor.
- ATP driven luminescence, which requires the presence of an oxidized partner on the water side of photosystem II, and involves electron transport from QB to QA.
- ΔpH driven reverse electron flow, which does not require the participation of the ATP synthase, and uses reduced intermediates between the two photosystems as electron donors for the reduction of QA.
- ΔpH driven luminescence which again uses reduced intermdiates between the two photosystems as electron donors for QA reduction, and requires the presence of an oxidized partner on the water side of photosystem II.
7.
- The transport of guanine in autospores of light-dark synchronizedChlorella fusca was studied using radioactive guanine in the concentration range of 4 nM to 50 μM.
- The transport system was constitutive, it had high specificity for the permeant, and theQ 10 value was in the range of 1.5 to 2.2. At concentrations lower than 0.2 μM the half saturating constant, S0.5 was 1 μM both for cells kept in dark and cells kept in light. At higher concentrations the S0.5 of darkened cells was about 0.23 μM, while that of illuminated cells was unchanged. Only above 0.2 μM guanine did illumination of the cells or addition of glucose increase the transport rate.
- Guanine which had accumulated did not leak out at temperatures below 45°C or by treatment with 10 μM dinitrophenol, which completely inhibited transport. Furthermore, the accumulated guanine did not exchange with exogenous guanine.
- The guanine accumulated, more than 105-fold over the external concentration, showing that the transport, was active.
- The initial transport rate per cell revealed annual fluctuations.
8.
Characteristics of thermoluminescence glow curves were compared in three types of Euglena cells: (i) strictly autotrophic, Cramer and Myers cells; (ii) photoheterotrophic cells sampled from an exponentially growing culture containing lactate as substrate repressing the photosynthetic activity; (iii) semiautotrophic cells, sampled when the lactate being totally exhausted, the photosynthesis was enhanced.In autotrophic and semiautotrophic cells, composite curves were observed after series of two or more actinic flashes fired at –10°C, which can be deconvoluted into a large band peaking in the range 12–22°C and a smaller one near 40°C, This second band presents the characteristics of a typical B band (due to S2/3QB
- recombination), whereas the first one resembled the band, shifted by -15–20°C, which is observed in herbicide resistant plants. The amplitude of this major band, which was in all cases very low after one flash, exhibited oscillations of period four but rapidly damping, with maxima after two and six flashes. In contrast, photoheterotrophic Euglena displayed single, non-oscillating curves with maxima in the range 5–10°C.In autotrophic and semiautotrophic cells, oxidizing pretreatments by either a preillumination with one or more (up to twenty-five) flashes, or a far-red preillumination in the presence of methylviologen, followed by a short dark period, induced thermoluminescence bands almost single and shifted by +3–5°C, or +12°C, respectively. In autotrophic cells, far-red light plus methyl viologen treatment induced a band peaking at 31°C, as in isolated thylakoids from Euglena or higher plants, while it had barely any effect in photoheterotrophic cells.Due to metabolic activities in dark-adapted cells, a reduction of redox groups at the donor and acceptor sides of PS II dark-adapted cells is supposed to occur. Two different explanations can be proposed to explain such a shift in the position of the main band in dark-adapted autotrophic control. The first explanation would be that in these reducing conditions a decreasing value of the equilibrium constant for the reaction: SnQA
-QBSnQAQB
-, would determine the shift of the main TL band towards low temperatures, as observed in herbicide resistant material. The second explanation would be that the main band would correspond to peak III already observed in vivo and assigned to S2/3QB
2- recombinations.Abbreviations CM
Cramer and Myers
- D1
a 32 kDa protein component of the PS II reaction center, psbA.gene product
- D2
a 34 kDa protein component of the PS II reaction center, psbD gene product
- FR
lar-red illumination
- Lexpo and Lstat
cells from lactate culture samples at exponential and stationary phase of growth
- MV
methylviologen
- pBQ
parabenzoquinone
- PQ
plastoquinone
- PS II
photosystem II
- QA
primary quinone electron acceptor
- QB
secondary quinone electron acceptor
- TL
thermoluminescence 相似文献
9.
Kenneth M. Towe 《Origins of life and evolution of the biosphere》1985,15(4):235-250
In the absence of direct evidence concerning the nature of the early Earth environments, it is acceptable under the uniformitarian principle to attempt to define primitive habitats from modern procaryotic physiology. Combining the rock and fossil record with present phylogenetic reconstuctions, application of this paleoecological approach to the evolutionary biochemistry and physiology of nitrogen fixation and photosynthesis leads to several inferences about the nature of Archean environments:
- To stimulate nitrogenase evolution and avoid its repression, the activity of the NH 4 + ion was less than 10?3, and probably lower.
- To be consistent with a moderately protective ozone screen, while not also repressing nitrogenase activity, incursions of abiotic dissolved oxygen at levels in the range 10?1.2?10?3.5 PAL would have been acceptable.
- To induce the formation and activity of RuBP carboxylase, the pCO2 was less than 100 PAL.
- To support Photosystem I activity, sulfide concentrations of at least 10?4 M were present in the photic zone.
- To avoid a too-rapid oxidation of sulfide, the pH was probably between 6–7, where H2S exceeds HS?.
- Lowering the sulfide to < 10?4 M to inhibit Photosystem I.
- Raising the pH above neutral (HS? > H2S), to mediate more rapid oxidation of HS?.
- Maintaining either an illumination below 300–400 lux (to avoid photosynthetic O2 self-repression of nitrogen fixation), or an adequate local source of combined nitrogen (aNH 4 + > 10?4) to repress nitrogen fixation entirely.
10.
Jack Farineau 《Photosynthesis research》1993,36(1):25-34
Characteristics of thermoluminescence (TL) glow curves were studied in thylakoids (isolated from pea leaves) or in intact pea leaves after an exposure to very high light for 2 min in the TL device. The inhibition of photosynthesis was detected as decreases of oxygen evolution rates and/or of variable fluorescence.In thylakoids exposed to high light, then dark adapted for 5 min, a flash regime induced TL glow curves which can be interpreted as corresponding to special B bands since: 1) they can be fitted by a single B band (leaving a residual band at –5°C) with a lower activation energy and a shift of the peak maximum by –5 to –6°C and, 2) the pattern of oscillation of their amplitudes was normal with a period of 4 and maxima on flashes 2 and 6. During a 1 h dark adaptation, no recovery of PS II activity occurred but the shift of the peak maximum was decreased to –1 to –2°C, while the activation energy of B bands increased. It is supposed that centers which remained active after the photoinhibitory treatment were subjected to reversible and probably conformational changes.Conversely, in intact leaves exposed to high light and kept only some minutes in the dark, TL bands induced by a flash regime were composite and could be deconvoluted into a special B band peaking near 30°C and a complex band with maximum at 2–5°C. In the case of charging bands by one flash, this low temperature band was largely decreased in size after a 10 min dark adaptation period; parallely, an increase of the B band type component appeared. Whatever was the flash number, bands at 2–5°C were suppressed by a short far red illumination given during the dark adaptation period and only remained a main band a 20°C; therefore, the origin of the low temperature band was tentatively ascribed to recombinations in centers blocked in state S2QA
–QB
2–. In vivo, the recovery of a moderately reduced state in the PQ pool, after an illumination, would be slow and under the dependence of a poising mechanism, probably involving an electron transfer between cytosol and chloroplasts or the so-called chlororespiration process.Abbreviations Ea-
activation energy
- FR-
far-red
- MV-
methylviologen
- pBQ-
p-benzoquinone
- PQ-
plastoquinone
- PS II-
Photosystem II
- QA-
primary quinone electron acceptor of PS II
- QB-
secondary quinone electron acceptor of PS II
- TL-
thermoluminescence 相似文献
11.
Measurements are reported on μs delayed light emission, following a single 10 ns excitation flash, in Alaska pea thylakoids treated with hydroxylamine (NH2OH) or with silicomolybdate.
- In thylakoids treated with 2 mM NH2OH in the light, or in the dark, the quantum yield of delayed light emission is considerably enhanced. A 10 μs lifetime component of delayed light emission is not significantly changed, whereas a 50–70 μs lifetime component is increased. MnCl2 and diphenylcarbazide are unable to reverse the above effects of NH2OH treatment. Thus Mn2+ and diphenylcarbazide must not donate electrons directly to reaction center II but on the oxygen-evolution side of the NH2OH block.
- When the closed form of photosystem II reaction centers (P680Q-), where P680 is the reaction center chlorophyll and Q is a ‘stable’ electron acceptor, is generated by preillumination of NH2OH-treated thylakoids with diuron present, the μs delayed light emission is inhibited, but a low level residual delayed light emission remains. Possible origins of this emission are discussed. It is believed that the best explanation for residual DLE is the existence of another acceptor besides Q that partakes in charge separation and rapid dissipative recombination when the reaction center is in the P680Q- state.
- The quantum yield of delayed light emission from ‘closed’ reaction centers (P680 +Q-) that have all charge stabilization reactions (i.e., flow of electrons to P680 + and out of Q-) blocked by NH2OH treatment and addition of diuron is 1.1×10-3 for components measured in a range from 6 to 400 μs and extrapolated to zero time.
- The addition of silicomolybdate, which accepts electron from Q-, causes delayed light emission in the μs range to be greatly inhibited.
12.
J. Wulf 《European biophysics journal : EBJ》1982,8(3):173-187
Extracellular recordings from the vacoule of photoreceptor cells of Hirudo medicinalis L. were performed using microelectrodes. The cells were adapted by white light flashes given at constant intervals (20 s). Response height versus relative intensity curves obtained from the same cell in physiological saline (PS) and in bathing solutions of either a) lowered calcium contents (2 ΜM/1 or less) or b) raised calcium contents (15 mM/1) were compared. The cells' adaptation state in PS was operationally defined by the ratio Q=h A /h S where h A is the response height evoked by the adapting flashes, and h S is the corresponding saturation response height. Sensitivity changes were measured by the half saturation intensity shift. Lowering extracellular calcium resulted in:
- The response height increased and the shape of the response became more rounded and prolonged.
- The total resistance between the vacuole and outside decreased from 8.2±1.4 MΩ (n=6) in PS to 4.6±0.4 MΩ (n=5). The resistance was independent of the cells' adaptation state.
- A change of the cells' sensitivity occured either in direction to light adaptation or in direction to dark adaptation. It depended functionally on the ratio Q:
13.
Thermoluminescence and delayed luminescence investigations of the autotrophically and photoheterotrophically cultivated green alga, Chlamydobotrys stellata, demonstrated that both the thermoluminescence and delayed luminescence yields are much lower in the photoheterotophic algae than in the autotrophic ones due to an efficient luminescence quenching of unknown mechanism. The relative contributions of the so called Q (S2Q?A charge recombination) and B (S2Q?B and S3Q?B charge recombinations) thermoluminescence bands to the glow curve as well as the QA(S2Q?B charge recombination) and QB (S2Q?B and S3Q?B charge recombinations) delayed luminescence components to the delayed luminescence decay of autotrophically and photoheterotrophically cultivated Chl. stellata were compared using a computer assisted curve resolution method. It was found that, while in the autotrophic cells the area of the B band was considerably larger than of the Q band, in photoheterotrophic cells the Q band was more effectively charged than the B band. In the delayed luminescence decay curves measured in the seconds to minutes time region the amplitude of the QA component relative to that of the QB component was larger in the photoheterotrophic cells than in the autotrophic ones. These observations demonstrate that, after light-induced charge separation in the photosystem II reaction centers of autotrophic cells, electrons are “quasipermanently” stored mainly in the secondary quinone acceptor pool, QB but in the nonquenched photosystem II reaction centers of photoheterotrophic cells the main reservoir of electrons is the primary quinone acceptor, QA. This behaviour indicates an inhibition of electron transport in the photoheterotrophic alga at the level of the secondary quinone acceptor, QB. 相似文献
14.
The recently developed technique of Magneto-Optical Difference Spectroscopy (MODS) [10] has been applied to reaction centers (RC) of the photosynthetic bacterium Rhodopseudomonas sphaeroides R-26. Absorbance changes induced by a magnetic field are measured as a function of wavelength yielding the triplet-minus-singlet (T-S) absorbance difference spectrum. (T-S) spectra thus obtained have been measured from 24–290 K. Going from low to high temperature the (T-S) spectra show the following features:
- A rapid decrease of positive absorption bands at 809 and 819 nm.
- A slow appearance of a band shift at 798 nm.
- A shift of the peak wavelength of the Qy absorbance band of the primary donor P-860 from 992 to 861 nm, and of its Qx band from 603 to 600 nm.
15.
In the glow curves of chloroplasts excited by a series of flashes at +1°C the intensity of the main thermoluminescence band appearing at +30°C (B band; B, secondary acceptor of Photosystem II) exhibits a period-4 oscillation with maxima on the 2nd and 6th flashes indicating the participation of the S3 state of the water-splitting system in the radiative charge recombination reaction. After long-term dark adaptation of chloroplasts (6 h), when the major part of the secondary acceptor pool (B pool) is oxidized, a period-2 contribution with maxima occurring at uneven flash numbers appears in the oscillation pattern. The B band can even be excited at ?160°C as well as by a single flash in which case the water-splitting system undergoes only one transition (S1 → S2). The experimental observations and computer simulation of the oscillatory patterns suggest that the B band originates from charge recombination of the S2B? and S3B? redox states. The half-time of charge recombination responsible for the B band is 48 s. When a major part of the plastoquinone pool is reduced due to prolonged excitation of the chloroplasts by continuous light, a second band (Q band; Q, primary acceptor of Photosystem II) appears in the glow curve at +10°C which overlaps with the B band. In chloroplasts excited by flashes prior to DCMU addition only the Q band can be observed showing maxima in the oscillation pattern at flash numbers 2, 6 and 10. The Q band can also be induced by flashes after DCMU addition which allows only one transition of the water-splitting system (S1 → S2). In the presence of DCMU, electrons accumulate on the primary acceptor Q, thus the Q band can be ascribed to the charge recombination of either the S2Q? or S3Q? states depending on whether the water-splitting system is in the S2 or the S3 state. The half-time of the back reaction of Q? with the donor side of PS II (S2 or S3 states) is 3 s. It was also observed that in a sequence of flashes the peak positions of the Q and B bands do not depend on the advancement of the water-splitting system from the S2 state to the S3 state. This result implies that the midpoint potential of the water-splitting system remains unmodified during the S2 → S3 transition. 相似文献
16.
The influence of UV-B irradiation on photosynthetic oxygen evolution by isolated spinach thylakoids has been investigated using thermoluminescence measurements. The thermoluminescence bands arising from the S2QB
- (B band) and S2QA
– (Q band) charge recombination disappeared with increasing UV-B irradiation time. In contrast, the C band at 50°C, arising from the recombination of QA
- with an accessory donor of Photosystem II, was transiently enhanced by the UV-B irradiation. The efficiency of DCMU to block QA to QB electron transfer decreased after irradiation as detected by the incomplete suppression of the B band by DCMU. The flash-induced oscillatory pattern of the B band was modified in the UV-B irradiated samples, indicating a decrease in the number of centers with reduced QB. Based on the results of this study, UV-B irradiation is suggested to damage both the donor and acceptor sides of Photosystem II. The damage of the water-oxidizing complex does not affect a specific S-state transition. Instead, charge stabilization is enhanced on an accessory donor. The acceptor-side modifications decrease the affinity of DCMU binding. This effect is assumed to reflect a structural change in the QB/DCMU binding site. The preferential loss of dark stable QB
- may be related to the same structural change or could be caused by the specific destruction of reduced quinones by the UV-B light.Abbreviations Chl
chlorophyll
- DCMU
3-(3,4,-dichlorophenyl)-1,1-dimethylurea
- PS II
Photosystem II
- QA
first quinone electron acceptor of PS II
- QB
second quinone electron acceptor of PS II
- Tyr-D
accessory electron donor of PS II
- S0-S4
charge storage states of the water-oxidizing complex 相似文献
17.
The toxicity of heavy metals on photosystem 2 photochemistry, was investigated by monitoring Hill activity, fluorescence, and thermoluminescence properties of photosystem 2 (PS 2) in pea (Pisum sativum L. cv. Bombay) chloroplasts. In Co2+-, Ni2+- or Zn2+-treated chloroplasts 2,6-dichlorophenolindophenol-Hill activity was markedly inhibited. Addition of hydroxylamine which donates electrons close to PS 2 reaction center did not restore the PS 2 activity. Co2+-, Ni2+ or Zn2+ also inhibited PS 2 activity supported by hydroxylamine in tris (hydroxymethyl)aminomethane (Tris)-inactivated chloroplasts. These observations were confirmed by fluorescence transient measurements. This implies that the metal ions inhibit either the reaction center or the components of PS 2 acceptor side. Flash-induced thermoluminescence studies revealed that the S2Q?A charge recombination was insensitive to metal ion addition. The S2Q?B charge recombination, however, was inhibited with increase in the level of Co2+, Ni2+ or Zn2+. The observed sensitivity of S2?B charge recombination in comparison to the stability of S2Q?A recombination suggests that the metal ions inhibit at the level of secondary quinone electron acceptor. QB. We suggest that Co2+, Ni2+ or Zn2+ do not block the electron flow between the primary and secondary quinone electron acceptor, but possibly, directly modify QB site, leading to the loss of PS 2 activity. 相似文献
18.
R. M. Glantz 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1996,178(3):413-425
- Polarization sensitivity (PS) was examined in photoreceptors and lamina monopolar cells (LMCs) in two species of crayfish, Procambarus clarkii and Pacifasticus leniusculus. The measurements were made with intracellular recordings and broad field illumination.
- PS is about 40% greater in Pacifasticus than in Procambarus (Table 1). In both species the LMC stationary PS profiles (estimated with flashes) are similar to those of receptors (Figs. 1 and 2). Both receptor and LMC sensitivity profiles are well described by cos2 θ functions (Fig. 3). PS was observed in all receptors and 78% of LMCs.
- When stimulated with a rotating polarizer, receptors and LMCs exhibit membrane potential modulation with phase predicted by the stationary PS profile (Fig. 5). In photoreceptors, the polarization-elicited percent modulation falls off steeply as intensity increases. The LMC modulation is stronger than that in receptors and relatively insensitive to the mean intensity (Figs. 6 to 8). For low intensities the LMC modulation is 100%. The LMC dynamic behavior is consistent with either an opponency mechanism or strong but polarization-insensitive lateral inhibition.
- Receptors and LMCs exhibit steady-state differential sensitivity to stationary e-vector orientation (Fig. 9).
- About 10% of the LMC neurons exhibit PS maxima separated by 90°. These results imply a nonlinear summation of signals from orthogonal receptor channels (Fig. 10).
19.
A recent development of kinetic light-scattering and -absorption photometry is described. Essential points are:
- In the scattering experiment, amplitude resolution of 2 · 10?5 (single flash) by application of a differential detector, stability of the same magnitude due to optical compensation, high intensity at the detector due to special optics for the scattered light and semiconductor sources.
- In the absorption measurement, elimination of scattering contributions by the dual wavelength-method and by high aperture optics.
- Simultaneous measurement of absorption and scattering. The application of the method is described in using signals from isolated bovine rod outer segments. A reliable procedure is described by the use of which the originally measured light-scattering effects can be split up into single signals.
20.
Klaus-Rüdiger Peters 《Archives of microbiology》1974,97(1):115-127
- Polyhedral particles were isolated from cells of Nitrobacter winogradskyi and of Nitrobacter strains K1, K4 and α1. Their physical and biological properties are characterized.
- The investigated strains contain polyhedral particles, 1000–1200 Å in size. With increasing age of the culture more particles are found in cells of Nitrobacter. Simultaneously the number of colony producing nitritoxidants decreases.
- In strain α1 the loss of the capability to form colonies is connected with partial lysis of the cell and release of particles.
- A homogeneous fraction of particles was obtained by zone density gradient centrifugation in Tris-Mg-SH-buffer.
- The polyhedral particles have a sedimentation coefficient of s w,20 0 =825S and a CsCl-buoyant density of ?25 g/cm3.
- Based on the determined properties the particles are classified as phage-like Nitrobacter particles Nb1.