Changes In Fluorescence Yield Research Articles

Spectroscopic studies of Eu 3+ doped calibo glass: Effect of the addition of barium carbonate, energy transfer in the presence of Sm 3+

Optical properties of Eu 3+ doped calibo glass has been studied in presence and absence of BaO and their dependence on BaO concentration explored. It is found that the fluorescence intensity increases and approaches maximum for 10% of BaO content but get quenched for higher concentrations. The energy transfer between two asimilar rare earth ions (Sm 3+:Eu 3+) doped in calibo glass has been verified on the basis of changes in fluorescence yield.

Light-Triggered Action Potentials and Changes in Quantum Efficiency of Photosystem II in Anthoceros Cells

Capillary microelectrodes and pulse amplitude-modulated microfluorometry were used to study light-triggered changes in cell membrane potential, chlorophyll fluorescence, and photochemical yield of PSII in chloroplasts of a hornwort Anthoceros sp. The action potential was generated by illuminating the plant sample for a few seconds. It was accompanied by a reversible decrease in quantum efficiency of PSII and by nonphotochemical quenching of fluorescence that continued as long as 10 min after the light stimulus. The presence of ammonium ions (2 mM) enhanced the amplitude and prolonged the duration of dark changes of fluorescence parameters in accordance with the reported increase in duration and amplitude of the light-triggered action potential in the presence of NH 4 + . A rapid retardation of PSII activity within the first seconds of illumination was also evident from absorbance changes at 810 nm reflecting the redox conversions of chlorophyll P700. The PSII-dependent stage of reduction in the induction curves of P700 absorbance was strongly suppressed, and the amplitudes of signals induced by white and far-red light (717 nm) differed insignificantly. It is concluded that a short-term irradiation triggers the generation of ΔpH at the thylakoid membranes, which is accompanied by inhibition of the plasma membrane H+ pump and by reversible inactivation of PSII due to increased thermal dissipation of chlorophyll excitations.

The impact of spectral composition and light periodicity on the activity of two antioxidant enzymes (SOD and CAT) in the coral Favia favus

In oligotrophic waters the light spectrum is mostly blue, and therefore the physiological and biochemical responses to blue light occurring in the coral tissue and in the symbiotic algae are important. Examination of the wavelength dependence of two free radical scavenger enzyme activity revealed an increase in activity in the blue light range (440–480 nm) compared to the red (640–680 nm) in the full visible light (400–700 nm) range. These data show for the first time the relationship between the action spectra of photosynthesis and the activity of two main antioxidant enzymes in the symbiotic coral Favia favus. It was found that in the animal (host) the enzyme response to the spectral distribution of light was higher than that of the zooxanthellae, probably due to accumulation of free radicals within the host tissue. Furthermore, we found that the activity of these enzymes is affected in nature by the length of the day and night, and in the laboratory, by the duration of the illumination. Changes in the pigment concentrations were also observed in response to growth under the blue region and the whole PAR spectrum, while fluorescence measurements with the fast repetition rate fluorometer (FRRF) showed a decrease in the sigma cross section and a decrease in the quantum yield also in the blue part of the spectrum. These changes of scavenger enzymes activity, pigment concentration and fluorescence yield at different light spectra are vital in acclimatization and survival of corals in shallow water environments with high light radiation.

Effect of exogenous histidine on restoration of electron transfer on the donor side of Photosystem II depleted of Mn

It is shown that restoration of photoinduced electron flow with added Mn2+ (measured by photoreduction of DCPIP and photoinduced change of chlorophyll fluorescence yield) in Mn-depleted Photosystem II (PS II) membrane fragments isolated from spinach chloroplasts, is considerably increased by exogenous histidine (His). The stimulating effect of His is not observed if other electron donors (NH2OH or diphenylcarbazide) are used instead of Mn2+. His added alone does not induce electron transfer in Mn-depleted PS II preparations. Investigation of pH dependence of the stimulating effect of 2 mM His shows that the effect is observed only at pH > 5.0, it gives a 50% activation around pH 6.0 and saturates at pH 7.0-7.5. Nearly 200 microM His is required for a 50 effect at pH 7.0. It is suggested that the added His can be involved in stimulation of electron transfer on the donor side of PS II through direct interaction of Mn2+ with deprotonated form(s) of His resulting in formation of Mn-His complexes capable of efficient electron donation to PS II (though it is not excluded that His serves as a base that takes part in proton exchange coupled with redox reactions on the donor side of PS II or as an electron donor to the oxidized Mn).

Contrasting modes of regulation of PS II light utilization with changing irradiance in normal and psbS mutant leaves of Arabidopsis thaliana.

Complementary techniques of chlorophyll a fluorescence, steady state CO(2) exchange, and O(2) release during a multiple turnover flash were applied to compare responses to irradiance for leaves of wild type and psbS mutants. The latter included variants in which the psbS gene was deleted (npq4-1) or possessed a single point mutation (npq4-9). Nonphotochemical quenching (NPQ) was reduced by up to 80 and 50%, respectively, in these lines at high irradiance. Analysis of changes in steady-state fluorescence yields and quantum yield of linear electron transport in the context of the reversible radical pair model of Photosystem II (PS II) indicated that NPQ occurs by nonradiative deactivation of chlorophyll singlet states in normal leaves. In contrast, application of the same criteria together with the observed irreversibility of NPQ and decline in density of functional PS II reaction centers following excessive illumination indicated a change in reaction center properties for the psbS deletion phenotype (Npq4-1(-)). Specifically, PS II reaction centers in Npq4-1(-) convert to a photochemically inactive, yet strongly quenching, form in intense light. The possibility of formation of a carotenoid or chlorophyll cation quencher in the reaction center is discussed. Results for the point mutant phenotype (Npq4-9(-)) were intermediate to those of wild-type and Npq4-1(-). Furthermore, wild-type leaves exhibited a significant reversible increase in the PS II in vivo rate constant for photochemistry (k(P0)) in saturating compared to limiting light. Changes in k(P0) could not be accounted for in terms of a classic phosphorylation-dependent (state transition) mechanism. Changes in k(P0) may arise from alternate pigment-protein conformations that alter the way excitons equilibrate among PS II chromophores. The lack of similar irradiance-dependent changes in k(P0) for the psbS mutants suggests a role for the PS II-S protein in the regulation of exciton distribution.

Photo-electrochemical control of photosystem II chlorophyll fluorescence in vivo

The effect of electric field on chlorophyll fluorescence is considered on the basis of the reversible radical pair model. The hypothesis is presented that the electric fields generated by photosynthetic charge separation in reaction centers and propagated laterally through the thylakoid lumen are associated with changes in chlorophyll fluorescence yield.

The rate of charge recombination in Photosystem II

Loss by recombination of the charge separated state P 680 +Q A − limits the performance of Photosystem II (PS II) as a photochemical energy converter. Time constants reported in literature for this process are mostly either near 0.17 ms or near 1.4 ms. The shorter time is found in plant PS II when reduction of P 680 + by the secondary electron donor Tyrosine Z cannot occur because Y Z is already oxidized. The 1.4 ms recombination is seen in Y Z-less mutants of the cyanobacterium Synechocystis. However, the rate of P 680 +Q A − recombination that actually competes with the stabilization of the charge separation has not been previously reported. We have measured the kinetics of the flash-induced fluorescence yield changes in the microsecond time domain in Tris-washed spinach chloroplasts. In this way the kinetics and yield of P 680 + reduction by Y Z were obtained, and the rate of the competing P 680 +Q A − recombination could be evaluated. The recombination time was less than 0.5 ms; the best-fitting time constant was 0.1 ms. The presence of Y Z ox slightly decreased the efficiency of excitation trapping but did not seem to accelerate P 680 +Q A − recombination. The two P 680 +Q A − lifetimes in the literature probably reflect a significant difference between plant and cyanobacterial PS II.

Fluorescence patches in high-frequency internal waves

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 235:29-42 (2002) - doi:10.3354/meps235029 Fluorescence patches in high-frequency internal waves Cleridy E. Lennert-Cody1,*, Peter J. S. Franks2 1Inter-American Tropical Tuna Commission, 8604 La Jolla Shores Drive, La Jolla, California 92037-1508, USA 2Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92093-0218, USA *E-mail: clennert@iattc.org ABSTRACT: Phytoplankton patchiness associated with high-frequency internal waves was investigated by analyzing chlorophyll fluorescence along isotherms. In summer, patches of fluorescence were found over wave troughs through the upper part of the water column and occasionally under wave crests deeper down. A similar pattern was observed in spring; day-to-day variability in the vertical structure of fluorescence patchiness was however greater in spring than in summer. Maximum fluorescence within patches was typically less than 130% of the background fluorescence, ranging from 104 to 168% in spring and 102 to 153% in summer. The largest values were generally found along isotherms nearest the surface. The patterns of fluorescence and wave form, with additional data on beam attenuation coefficient, were used to test hypotheses of patch formation mechanisms, including non-photochemical quenching, swimming-gradient induced patchiness, and concentration-gradient induced patchiness. While non-photochemical quenching apparently created patches of fluorescence, the magnitude and pattern of the patches could not be completely accounted for by this dynamic. Much of the patchiness was consistent with increases in biomass driven by swimming of phytoplankton in the divergent wave circulation. The contribution of any mechanism to patch formation depends on the phytoplankton community structure: blooms dominated by dinoflagellates will show patches created by swimming and changes in fluorescence yield, while the non-swimming phytoplankton community will tend to show patches of enhanced fluorescence yield. KEY WORDS: Patchiness · Phytoplankton · Fluorescence · Internal waves Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 235. Online publication date: June 19, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.

Changes in Chlorophyll a Fluorescence, Lipid Peroxidation, and Detoxificant System in Potato Plants Grown under Filtered and Non-Filtered Air in Open-Top Chambers

Its high oxidant capacity and ability to generate reactive oxygen species cause ozone toxicity. We studied the effect of ambient ozone on chlorophyll (Chl) a fluorescence, antioxidant enzymes, ascorbate contents, and lipid peroxidation in potatoes grown in open-top chambers in the field. In plants grown in non-filtered air (NFA), the development of non-photochemical quenching brought about a decrease in photosystem 2 (PS2) photochemical efficiency. Also the ability of PS2 to reduce the primary acceptor QA was lower than in charcoal-filtered, ozone-free air (CFA). Changes in Chl fluorescence yield were associated with changes in the thylakoid membrane. Ozone altered chloroplast membrane properties, as indicated by an increase in membrane lipid peroxidation in FNA-leaves compared to CFA plants. The ascorbate pool and activities of antioxidant enzymes were used for an indication of the detoxification system state in NFA and CFA leaves, whereby ozone affects the ascorbate concentration and decreases the antioxidant enzymes activities. The capacity of both detoxifying systems together was not high enough to protect potato plants against ambient ozone concentrations which reduced the photosynthetic yield in this potato cultivar.

Secondary stabilization reactions and proton-coupled electron transport in photosystem II investigated by electroluminescence and fluorescence spectroscopy.

The oxidized primary electron donor in photosystem II, P(680)(+), is reduced in several phases, extending over 4 orders of magnitude in time. Especially the slower phases may reflect the back-pressure exerted by water oxidation and provide information on the reactions involved. The kinetics of secondary electron-transfer reactions in the microseconds time range after charge separation were investigated in oxygen-evolving thylakoids suspended in H2O or D2O. Flash-induced changes of chlorophyll fluorescence yield and electric field-induced recombination luminescence were decomposed into contributions from oxidation states S(0), S(1), S(2), and S(3) of the oxygen-evolving complex and interpreted in terms of stabilization kinetics of the initial charge-separated state S(j)Y(Z)P(680)(+)Q(A)(-)Q(B). In approximately 10% of the centers, only charge recombination took place. Otherwise, no static heterogeneity was involved in the microsecond reduction of P(680)(+) by Y(Z) (stabilization) or Q(A)(-) (recombination). The recombination component in active centers occurs mainly upon charge separation in S(3), and, in the presence of D2O, in S(2) as well and is tentatively attributed to the presence of Y(Z)(ox)S(j-1) in equilibrium with Y(Z)S(j). A 20-30 micros stabilization occurs in all S-states, but to different extents. Possible mechanisms for this component are discussed. D2O was found to decrease: (i) the rate of the reaction Y(Z)(ox)S(1) to Y(Z)S(2), (ii) the equilibrium constant between P680(+)Y(Z)S(2) and P(680)Y(Z)(ox)S(2), (iii) the rate of the slow phase of P(680)(+) reduction for the S(3) --> S(0) transition, and (iv) the rate of electron transfer from Q(A)(-) to Q(B) /Q(B)(-). The increased 'miss probability' in D2O is due to (iii).

Xanthophyll cycle-dependent nonphotochemical quenching in Photosystem II: Mechanistic insights gained from Arabidopsis thaliana L. mutants that lack violaxanthin deepoxidase activity and/or lutein.

This study compares Photosystem II (PS II) chlorophyll (Chl) a fluorescence yield changes of Arabidopsis thaliana L. nuclear gene mutants, thoughtfully provided by the authors of Pogson et al. (1998 Proc Natl Acad Sci USA 95: 13324-13329). One single mutant (npq1) inhibits the violaxanthin deepoxidase that converts violaxanthin to antheraxanthin and zeaxanthin. A second single mutant (lut2) inhibits the in-cyclization enzyme step between lycopene and beta,in-carotene causing accumulation of beta,beta-carotene derivatives, primarily the violaxanthin cycle pigments, at the expense of lutein. The double mutant (lut2-npq1) incorporates both lesions. PS II Chl a fluorescence was characterized in leaves and thylakoids using both steady state and time-resolved methods, the intrathylakoid pH was estimated by 9-aminoacridine fluorescence quenching and chloroplast pigments were determined by HPLC. Under maximal PS II Chl a fluorescence intensity conditions without intrathylakoid acidification, the main 2 nanosecond (ns) fluorescence lifetime distribution mode parameters were similar for the WT and mutants both before and after illumination. The light and ATPase mediated intrathylakoid pH levels were also similar and caused similar changes in the fluorescence lifetime distribution widths and centers for the WT and each mutant. The npq1 exhibited low antheraxanthin and zeaxanthin and high violaxanthin levels and the uncoupler-sensitive amplitudes of short (< 1 ns) PS II Chl a fluorescence distribution modes were strongly inhibited compared to the WT. Lutein deficiency coincided with pleiotropic effects on PS II energy dissipation and probably altered conformations of PS II carotenoid-chlorophyll binding proteins. The lut2 exhibited separate active and inactive pools of antheraxanthin and zeaxanthin with respect to all deepoxidation, epoxidation and fluorescence quenching activities. The active xanthophyll cycle pool in lut2 exhibited a lower ( approximately 35% of WT) concentration efficiency, for a given intrathylakoid pH, to increase the sub-nanosecond distribution amplitudes, which predicts and explains inhibited induction kinetics and fluorescence quenching. The lut2-npq1 mutant exhibited a constant pool of antheraxanthin and zeaxanthin, no deepoxidation and little or no pH-reversible fluorescence decrease. It is concluded that in addition to intrathylakoid acidification, a certain level of zeaxanthin and antheraxanthin (or lutein) is absolutely required for the major reversible component of PS II Chl a fluorescence quenching.

Iron deficiency interrupts energy transfer from a disconnected part of the antenna to the rest of Photosystem II.

Iron deficiency changed markedly the shape of the leaf chlorophyll fluorescence induction kinetics during a dark-light transition, the so-called Kautsky effect. Changes in chlorophyll fluorescence lifetime and yield were observed, increasing largely the minimal and the intermediate chlorophyll fluorescence levels, with a marked dip between the intermediate and the maximum levels and loss of the secondary peak after the maximum. During the slow changes, the lifetime-yield relationship was found to be linear and curvilinear (towards positive lifetime values) in control and Fe-deficient leaves, respectively. These results suggested that part of the Photosystem II antenna in Fe-deficient leaves emits fluorescence with a long lifetime. In dark-adapted Fe-deficient leaves, measurements in the picosecond-nanosecond time domain confirmed the presence of a 3.3-ns component, contributing to 15% of the total fluorescence. Computer simulations revealed that upon illumination such contribution is also present and remains constant, indicating that energy transfer is partially interrupted in Fe-deficient leaves. Photosystem II-enriched membrane fractions containing different pigment-protein complexes were isolated from control and Fe-deficient leaves and characterized spectrophotometrically. The photosynthetic pigment composition of the fractions was also determined. Data revealed the presence of a novel pigment-protein complex induced by Fe deficiency and an enrichment of internal relative to peripheral antenna complexes. The data suggest a partial disconnection between internal Photosystem II antenna complexes and the reaction center, which could lead to an underestimation of the Photosystem II efficiency in dark-adapted, low chlorophyll Fe-deficient leaves, using chlorophyll fluorescence.

Diurnal and bathymetric changes in chlorophyll fluorescence yields of reef corals measured in situ with a fast repetition rate fluorometer

A newly developed underwater fast repetition rate fluorometer (FRRF) was used for in situ measurements of chlorophyll fluorescence yields on the reef-building corals Montastraea faveo- lata and Montastraea cavernosa from around Lee Stocking Island, Bahamas. Diel studies of the quan- tum yield of chlorophyll fluorescence (⌉F '/ Fm') in photosystem II (PSII) reveal a pattern of mid-day depression of ⌉F '/ Fm' in both of these species of coral. At the same time, non-photochemical quench- ing (qN ) increased significantly during the day, a pattern consistent with the regulation of PSII by dynamic photoinhibition mediated by non-photochemical quenching. Despite these mid-day depres- sions in ⌉F '/ Fm', net productivity, measured as oxygen flux, remains high, suggesting that non-pho- tochemical quenching dissipates the majority of the absorbed photons at mid-day and protects the photosynthetic apparatus, allowing the endosymbiotic dinoflagellates (zooxanthellae) to operate at maximum rates of photosynthesis. In 1999 measurements of ⌉F '/ Fm' on M. faveolata over a bathy- metric range of 2 to 30 m showed an increase in ⌉F '/ Fm' with increasing depth when measured at the same time of day. This suggests, although there is year-to-year variability, that changes in the under- water light field, and photoacclimation to that light field, control the degree of photoprotection attrib- utable to non-photochemical quenching in the zooxanthellae of these corals. The fluorescence yields of M. faveolata exposed to elevated temperatures (> 32°C) in the field showed a significant decrease in ⌉F '/Fm' before visible signs (e.g., paling of colonies) occurred. It was also possible to predict which colonies at the same depth and light regime would bleach first in response to elevated temperatures before any visible signs of bleaching were evident using ⌉F '/Fm' as a predictor.

Study of the non-photochemical dark rise in chlorophyll fluorescence in pre-illuminated leaves of various C3 and C4 plants submitted to partial anaerobiosis

Changes in chlorophyll fluorescence yield were studied during a dark period in pre-illuminated leaves of various C3 and C4 plants. The oxygen content in the gaseous atmosphere was either normal (21 kPa) or low (1.5 or 0.36 kPa). C3 and C4 plants of the NAD malic enzyme subgroup showed an initial rise in fluorescence at the onset of the dark period with an amplitude depending on the O 2 level in the gas. In C4 plants belonging to the other two subgroups, the slow rise was absent or of very low size. At high [O 2], the fluorescence level decreased in some minutes to the initial F 0 level (determined in dark-adapted leaves). Conversely at low [O 2], the fluorescence yield remained higher than F 0 in all the C4 plants studied, whereas it decreased slowly to the F 0 level in the different C3 plants. At low [O 2], the fluorescence level decreased rapidly to F 0 when introducing for 30 s, a high O 2 level or when giving a 15-s far-red illumination. At the end of these treatments, the fluorescence level re-increased. These results demonstrate the presence at low [O 2] of highly fluorescent `closed' photosystem II centres containing Q - A in equilibrium with reduced plastoquinone molecules of the chloroplastic pool. Reoxidation of the plastoquinone pool would be dependent on the functioning of an oxidase probably dependent on a chlororespiration process fully active at O 2 levels higher than 2 kPa. The source of reducing equivalents for the plastoquinone pool is discussed.

Reconstruction of the Water‐Oxidizing Complex in Manganese‐Depleted Photosystem II Preparations Using Mononuclear Manganese Complexes

Abstract— The water‐oxidizing complex of chloroplast photosystem II is composed of a cluster of four manganese atoms that can accumulate four oxidizing redox equivalents. Depletion of manganese from the water‐oxidizing complex fully inhibits oxygen evolution. However, the complex can be reconstituted in the presence of exogenous manganese in a process called photoactivation. In the present study, mononuclear manganese complexes with ligands derived from either nitrosonaphthol and ethylenediamine (Niten) or from diaminohexane and salicylaldehyde (Salhxn) are used in photoactivation experiments. Measurements of photoinduced changes of chlorophyll fluorescence yield, thermal dissipation using photoacoustic spectroscopy, photoreduction of 2,6‐dichorophenolindophenol and oxygen evolution in manganese‐depleted and in reconstituted photosystem II preparations demonstrate that photoactivation is more efficient when Niten and Salhxn complexes are used instead of MnCl2. It is inferred that the aromatic ligands facilitate the interaction of the manganese atoms with photosystem II. The addition of CaCl2 and of the extrinsic polypeptide of 33 kDa known as the manganese‐stabilizing protein during photoactivation further enhances the recovery of electron transport and oxygen evolution activities. It is proposed that mononuclear manganese complexes are able to contribute to re‐constitution of the water‐oxidizing complex by sequential addition of single ions similarly to the current model for assembly of the tetranuclear manganese cluster and that these complexes constitute suitable model systems to study the assembly of the water‐oxidizing complex.

Light‐triggered electrical events in the thylakoid membrane of plant chloroplasts

An overview is given of electrical events that occur in plant chloroplasts in association with their energization and subsequent photosynthetic performance. Special emphasis is given to the measuring techniques, in particular application of patch‐clamp methods, which enable comparison of light‐induced photocurrent and ‐potential kinetics of the thylakoid with kinetics of changes in chlorophyll fluorescence yield.

Reconstruction of the Water-Oxidizing Complex in Manganese-Depleted Photosystem II Preparations Using Mononuclear Manganese Complexes

Abstract— The water-oxidizing complex of chloroplast photosystem II is composed of a cluster of four manganese atoms that can accumulate four oxidizing redox equivalents. Depletion of manganese from the water-oxidizing complex fully inhibits oxygen evolution. However, the complex can be reconstituted in the presence of exogenous manganese in a process called photoactivation. In the present study, mononuclear manganese complexes with ligands derived from either nitrosonaphthol and ethylenediamine (Niten) or from diaminohexane and salicylaldehyde (Salhxn) are used in photoactivation experiments. Measurements of photoinduced changes of chlorophyll fluorescence yield, thermal dissipation using photoacoustic spectroscopy, photoreduction of 2,6-dichorophenolindophenol and oxygen evolution in manganese-depleted and in reconstituted photosystem II preparations demonstrate that photoactivation is more efficient when Niten and Salhxn complexes are used instead of MnCl2. It is inferred that the aromatic ligands facilitate the interaction of the manganese atoms with photosystem II. The addition of CaCl2 and of the extrinsic polypeptide of 33 kDa known as the manganese-stabilizing protein during photoactivation further enhances the recovery of electron transport and oxygen evolution activities. It is proposed that mononuclear manganese complexes are able to contribute to re-constitution of the water-oxidizing complex by sequential addition of single ions similarly to the current model for assembly of the tetranuclear manganese cluster and that these complexes constitute suitable model systems to study the assembly of the water-oxidizing complex.

Chlorophyll fluorescence analysis of cyanobacterial photosynthesis and acclimation.

Cyanobacteria are ecologically important photosynthetic prokaryotes that also serve as popular model organisms for studies of photosynthesis and gene regulation. Both molecular and ecological studies of cyanobacteria benefit from real-time information on photosynthesis and acclimation. Monitoring in vivo chlorophyll fluorescence can provide noninvasive measures of photosynthetic physiology in a wide range of cyanobacteria and cyanolichens and requires only small samples. Cyanobacterial fluorescence patterns are distinct from those of plants, because of key structural and functional properties of cyanobacteria. These include significant fluorescence emission from the light-harvesting phycobiliproteins; large and rapid changes in fluorescence yield (state transitions) which depend on metabolic and environmental conditions; and flexible, overlapping respiratory and photosynthetic electron transport chains. The fluorescence parameters FV/FM, FV'/FM',qp,qN, NPQ, and phiPS II were originally developed to extract information from the fluorescence signals of higher plants. In this review, we consider how the special properties of cyanobacteria can be accommodated and used to extract biologically useful information from cyanobacterial in vivo chlorophyll fluorescence signals. We describe how the pattern of fluorescence yield versus light intensity can be used to predict the acclimated light level for a cyanobacterial population, giving information valuable for both laboratory and field studies of acclimation processes. The size of the change in fluorescence yield during dark-to-light transitions can provide information on respiration and the iron status of the cyanobacteria. Finally, fluorescence parameters can be used to estimate the electron transport rate at the acclimated growth light intensity.

On the origin of the `35-μs kinetics' of P680 +⋅ reduction in photosystem II with an intact water oxidising complex

The origin of the `35-μs kinetics' of P680 +⋅ reduction in photosystem II (PS II) with an intact water oxidising complex has been analysed by comparative measurements of laser flash induced changes of the 830-nm absorption and the relative quantum yield of chlorophyll (Chl) fluorescence. The latter parameter was monitored at a time resolution of 500 ns by using newly developed home built equipment [Reifarth, F., Christen, G. and Renger, G. (1997) Photosynth. Res. 51, 231–242]. It was found that: (i) the amplitudes of the unresolved ns-kinetics of both 830-nm absorption changes and the rise of fluorescence yield exhibit virtually the same period four oscillation pattern when dark adapted samples are excited with a train of saturating laser flashes; (ii) the corresponding oscillation patterns of the normalised extent of the 35-μs kinetics under identical excitation conditions are strikingly different with maxima after the 3rd and 5th flash for the 830-nm absorption changes vs. pronounced maxima after the 4th and 8th flash for the rise of the fluorescence yield. The period four oscillations unambiguously show that the `35-μs kinetics' of P680 +⋅ reduction are characteristic for reactions in PS II entities with an intact water oxidising complex. However, the disparity of the oscillation patterns of (ii) indicates that in contrast to the ns components of P680 +⋅ reduction the 35-μs kinetics do not reflect exclusively an electron transfer from Y Z to P680 +⋅. It is inferred that a more complex reaction takes place which comprises at least two processes: (a) P680 +⋅ reduction by Y Z and (b) coupled and/or competing reaction(s) which give rise to additional changes of the chlorophyll fluorescence yield.

Comparison of the Functional Properties of the Monomeric and Dimeric Forms of the Isolated CP47-Reaction Center Complex

Chlorophyll fluorescence, thermoluminescence, and EPR spectroscopy have been used to investigate the functional properties of the monomeric and dimeric forms of the photosystem II CP47-reaction center (CP47-RC) subcore complex that was isolated (Zheleva, D., Sharma, J., Panico, M., Morris, H. R., and Barber, J. (1998) J. Biol. Chem. 273, 16122-16127). Chlorophyll fluorescence yield changes induced either by the initiation of continuous actinic light or by repetitive light flashes indicated that the dimeric, but not the monomeric, form of the CP47-RC complex showed secondary electron transport properties indicative of QA reduction. Thermoluminescence measurements also clearly distinguished the monomer from the dimer in that the latter showed a ZV band, which appeared at -55 degreesC, following illumination at -80 degreesC. This band has been determined to be an indicator of the photoaccumulation of QA-. The ability of the dimeric CP47-RC to show secondary electron transport properties was clearly demonstrated by EPR studies. The dimer was characterized by organic radical signals at about g = 2 induced either by illumination or by the addition of dithionite. The dithionite-induced signal was attributed to QA-, but there was no indication of any interaction with non-heme iron. The signal induced by light was more complex, being composed not only of the QA- radical but also of radicals generated on the donor side. Difference analyses indicated that one of these radicals is likely to be due to a D1 tyrosine 161 or D2 tyrosine 161. In contrast, the monomeric CP47-RC complex did not show similar EPR-detectable radicals and instead was dominated by a high yield of the spin-polarized triplet signal generated by recombination reactions between the oxidized primary reductant, pheophytin, and the primary donor, P680. It is also concluded from EPR analyses that both the monomeric and dimeric forms of the CP47-RC subcore complex contain one cytochrome b559 per reaction center. Overall the results suggest that photosystem II normally functions as a dimer complex and that monomerization at the level of the CP47-RC subcore complex leads to destabilization of the bound plastoquinone, which functions as QA.