Excited-State Energy Level Does Not Determine the Differential Effect of Violaxanthin and Zeaxanthin on Chlorophyll Fluorescence Quenching in the Isolated Light-Harvesting Complex of Photosystem II

Abstract— The mechanism of action of xanthophyll cycle carotenoids in controlling the quenching of chlorophyll fluorescence in the major light-harvesting complex of photosystem II (LHCIIb) has been investigated. Auroxanthin, a diepoxy carotenoid with 7 conjugated carbon double bonds, violaxanthin (9 conjugated double bonds) and zeaxanthin (11 conjugated double bonds) have been compared with regard to their effects in vitro on fluorescence quenching and LHCIIb oligomerization. It was found that auroxanthin stimulated fluorescence quenching, similar to the effect of zeaxanthin and in contrast to the inhibition caused by violaxanthin. Auroxanthin caused an increase in the oligomerization of LHCIIb and an increase in relative emission of long-wavelength fluorescence at 77 K. It is concluded that auroxanthin can mimic the effect of zeaxanthin on LHCII, strongly suggesting that the xanthophyll cycle carotenoids control quenching in vitro by an indirect structural effect and not by direct quenching of chlorophyll excited states.     

LIGHT-INDUCED QUENCHING OF PHOTOSYSTEM II FLUORESCENCE AT 77 K

Abstract— Light-induced quenching of the low temperature fluorescence emission from photosystem II (PS II) at 695 nm ( F ₆₉₅) has been observed in chloroplasts and whole leaves of spinach. Photosystem I (PS I) fluorescence emission at 735 nm ( F ₇₃₅) is quenched to a lesser degree but this quenching is thought to originate from PS II and is manifest in a reduced amount of excitation energy available for spillover to PS I. Differential quenching of these two fluorescence emissions leads to an increase in the F ₇₃₅/ F ₆₈₅ ratio on exposure to light at 77 K. Rewarming the sample from -196°C discharges the thermoluminescence Z-band and much of the original unquenched fluorescence is recovered. The relationship between the thermoluminescence Z-band and the quenching of the low temperature fluorescence emission ( F ₆₉₅) is discussed with respect to the formation of reduced pheophytin in the PS II reaction center at 77 K.     

INFLUENCE OF CHANGES IN THE PHOTON PROTECTIVE ENERGY DISSIPATION ON RED LIGHT-INDUCED DETRAPPING OF THE THERMOLUMINESCENCE Z-BAND

-Thermoluminescence emission at 110 K (Z-band) was markedly diminished when thylakoid membranes were exposed to red light during or after Z-band charging with blue light. Analysis of this phenomenon showed that deactivation of Z-band-emitting chlorophyll species occurred preferentially on the low temperature side of the glow curve, and red light of670–680 nm was most efficient in the deactivation. In order to test our hypothesis that this detrapping is related to local heating effects caused by dissipation of absorbed energy, we measured thermoluminescence glow curves and Z-band emission spectra from spinach leaf discs and thylakoid membranes during induction of nonphotochemical chlorophyll fluorescence quenching. Pretreatment of the plant material was designed to achieve different levels of (1) de-epoxidized xanthophylls in the photosynthetic apparatus and (2) the proton concentration in the thylakoid lumen. In comparison, measurements were performed in aggregated and trimeric light-harvesting pigment-protein complexes of photosystem II. We observed on all three levels of organization that a higher capacity of excitation energy dissipation was accompanied by a stronger red light-induced detrapping of Z-band thermoluminescence.     

Aggregation of the Light-Harvesting Complex in Intact Leaves of Tobacco Plants Stressed by CO2 Deficit

Pronounced aggregation of the photosystem II light-harvesting complex (LHC II) was observed in low-lightgrown tobacco plants stressed with a strong CO₂ deficit for 2–3 days. The LHC II aggregates showed a typical band at 697–700 nm (F₆₉₉) in low-temperature emission spectra. Its excitation spectrum corresponded to that of detergent-solubilized LHC II. Formation of F₆₉₉ in stressed plants was not reversed in the dark and leaves did not contain any zeaxanthin showing that neither a light-induced transthylakoid pH gradient nor zeaxanthin was required for LHC II aggregation. The CO₂-stressed plants showed clear signs of photodamage: depression of the potential yield of photosystem II photochemistry (F,/F_M) by 50–70% and a decline in chlorophyll content by 10–15%. Therefore, we propose that the photodamage to the photosynthetic apparatus is the cause of the LHC II aggregation in plants. The F₆₉₉ exhibited a reversible decrease of its intensity upon irradiation of leaves with intensive light. There was no or only slight decrease around 700 nm in unstressed plants. The nonphotochemical quenching of chlorophyll fluorescence showed the opposite relation, being higher before than after the strong CO₂ deficit. This discrepancy was likely related to the different LHC II aggregation state in control and stressed plants.     

Regulation of the excitation energy utilization in the photosynthetic apparatus of chlorina f2 barley mutant grown under different irradiances

Acclimation of the photosynthetic apparatus of chlorophyll b-less barley mutant chlorina f2 to low light (100 micromolm(-2)s(-1); LL) and extremely high light level (1000 micromolm(-2)s(-1); HL) was examined using techniques of pigment analysis and chlorophyll a fluorescence measurements at room temperature and at 77 K. The absence of chlorophyll b in LL-grown chlorina f2 resulted in the reduction of functional antenna size of both photosystem II (by 67%) and photosystem I (by 21%). Chlorophyll fluorescence characteristics of the LL-grown mutant indicated no impairment of the utilization of absorbed light energy in photosystem II photochemistry. Thermal dissipation of excitation energy estimated as non-photochemical quenching of minimal fluorescence (SV(0)) was significantly higher as compared to the wild-type barley grown under LL. Despite impaired assembly of pigment-protein complexes, chlorina f2 was able to efficiently acclimate to HL. In comparison with chlorina f2 grown under LL, HL-grown chlorina f2 was characterized by unaffected maximal photochemical efficiency of photosystem II (F(V)/F(M), doubled content of both beta-carotene and the xanthophyll cycle pigments and considerably reduced efficiency of excitation energy transfer from carotenoids to chlorophyll a. The enormous xanthophyll cycle pool size was however associated with reduced SV(0) capacity. We suggest that the substantial part of the xanthophyll cycle pigments is not bound to the remaining pigment-protein complexes and acts as filter for excitation energy, thereby contributing to the efficient photoprotection of chlorina f2 grown under HL.     

Parallel changes in non-photochemical quenching properties, photosynthesis and D1 levels at sudden, prolonged irradiance exposures in Ulva fasciata Delile

The photosynthetic response to a sudden and prolonged high irradiance exposure and following recovery at low irradiance were studied with the aim of investigating the ability to withstand and adapt to high irradiance without prior high light adaptation. When thalli of Ulva fasciata, accustomed to a low irradiance (80 micromol photons m(-2) s(-1)), were exposed to a high irradiance (1500 micromol photons m(-2) s(-1)), the D1 protein was rapidly degraded, reaching a steady-state level after 110 min. This was followed by a fast recovery when thalli were transferred to dim light. The overall ability of non-photochemical quenching of chlorophyll fluorescence decreased and levelled off at a sudden and prolonged exposure to high irradiance and followed the same trend as the D1 level with a fast recovery in dim light. Ulva had intrinsic means to acclimate rapidly to high irradiance, when non-photochemical quenching did not operate properly, by maintaining a smaller fraction of high light tolerant PSII assemblages and by maintaining a high non-photochemical quenching capacity of chlorophyll fluorescence in relation to the variable fluorescence. The overall absorption of light (400-700 nm) remained high during the period of high irradiance exposure. When Ulva were deprived of nutrients in the form of PES media the ability of non-photochemical quenching decreased at photoinhibitory conditions. The possible causes for the responses at prolonged irradiance and the mechanisms for the decrease of non-photochemical quenching are discussed, with implications for field measurements.     

IN VIVO FLUORESCENCE SPECTROSCOPY OF CHLOROPHYLL IN VARIOUS UNRIPE AND RIPE FRUIT

—Low temperature (77 K) fluorescence emission spectra of slices obtained from the peel and various layers of the pericarp were recorded for fruits which remain green or undergo color break during ripening.
Fluorescence emission peaks characteristic of the photosystem II antennae (λ_F 686 nm) and reaction center (λ_F 696 nm), as well as of the photosystem I antenna (λ_F 730-740 nm), were present in the peel and all parts of the green pericarp of ripe kiwi, avocado and cantaloupe, as well as in ripe tomato and tangerine after color break. The pattern of the fluorescence emission spectra of all samples except that of the kiwi fruit was similar to that obtained from green photosynthetic tissue of leaves, indicating a normal organization of the chlorophyll-containing complexes of thylakoidal membranes. This pattern is characterized by a significantly higher emission at 730-740 nm relative to that of the 696 and 686 nm peaks. In contradistinction, the fluorescence emission at 686 and 696 nm was higher than that at 730 nm in the kiwi fruit, indicating a reduction in the size of the photosystem I antenna chlorophyll. In the innermost yellowish layers of the kiwi pericarp, a further loss of this antenna occurred, as well as disorganization of the photosystem II complex. The above conclusions are suggested also by measurements of variable fluorescence kinetics.
The results presented here indicate that fluorescence spectroscopy might be used as a tool for the study of chlorophyll organization during the growth and ripening periods of fruit.     

DELAYED EMISSION OF CHLOROPHYLL a AGGREGATES AND RHODAMINE 6G EMBEDDED IN POLYMER MATRIX*

Delayed luminescence (in the microsecond time range) of the chlorophyll (Chl) a“dry” form as well as hydrated dimers located in a polyvinylalcohol film was measured from room temperature down to 8 K. In the same matrix the delayed luminescence of rhodamine 6G (Rhod) was investigated. The delayed emission both of Chl a and Rhod is probably due to the formation and delayed recombination of a radical pair. It seems that this process occurs without participation of triplet states, as it does not reflect their well-known sensitivity to oxygen. The temperature dependence of the delayed luminescence of vanous Chl forms is different. In the region around 678 nm (dry monomer) delayed luminescence needs a thermal activation energy of about 0.03 eV, whereas at 740 nm (wet aggregates) delayed luminescence intensity increases linearly with decreasing temperature. Its assignment as a-type delayed luminescence from the low-lying triplet state can consistently be excluded from both the weak temperature dependence of the delayed fluorescence and its large intensity as compared to the prompt fluorescence. Delayed luminescence of Rhod is almost independent of temperature between 8 K and 300 K. The dependence of delayed luminescence intensity on exciting light intensity is linear at lower intensities and tends to saturation at higher. Therefore the delayed luminescence is not related to exciton annihilation. Positions and intensities of the Chl delayed luminescence bands show that it is not phosphorescence (β-type delayed luminescence). The aggregation of both Chl and Rhod molecules strongly influences delayed luminescence since it differs in several properties if excited in the monomer or in the aggregate absorption range. Every aggregational form of dye emits its characteristic delayed luminescence band.     

PHOTOSYSTEM II HETEROGENEITY IN THE MARINE DIATOM Phaeodactylum tricornutum

Abstract— The kinetics of photosystem II photochemistry are analyzed in the marine diatom Phaeodacfylum tricornutum by measurement of fluorescence induction in cell suspensions treated with 3–(3,4-dichlorophenyl)-1,1-dimethylurea. Photosystem II kinetics are found to be biphasic, the sum of two exponential components, suggesting that biphasic energy conversion in photosystem II may be a general consequence of thylakoid membrane appression. The emission wavelength-dependence of fluorescence induction suggests that the two photosystem II components have different variable fluorescence emission spectra. The slower component exhibits characteristic emission of the diatom light-harvesting complexes while emission from the faster component resembles that of the photosystem II reaction center. Variable fluorescence emission (293 K) at wavelengths > 700 nm is assigned to photosystem II. Application of model equations indicates that the two photosystem II unit types differ primarily in antenna size. A new analytical procedure is presented which eliminates ambiguities in the kinetic analysis associated with the incorrect assignment of the maximal fluorescence yield.     

Membrane potential is involved in regulation of photosynthetic reactions in the marine diatom Thalassiosira weissflogii

High-intensity Chl fluorescence transients (OJIP transients) and light-induced kinetics of the delayed light emission were measured in diatom microalga Thalassiosira weissflogii in the presence of various uncouplers and photosynthetic inhibitors. The I step in the OJIP transients in T. weissflogii was essentially reduced or completely absent but was restored in the presence of uncouplers valinomycin, FCCP, and nigericin. Moreover, valinomycin enhanced ΔpH-dependent non-photochemical fluorescence quenching following the OJIP rise. In the presence of valinomycin, the transthylakoid membrane potential was significantly inhibited as evaluated by measurements of the delayed light emission. The results suggest a membrane potential control of the fluorescence yield in T. weissflogii. Possible mechanisms underlying the observed effects of uncouplers are discussed.     

Changes in the energy distribution in mutant thylakoid membranes of pea with modified pigment content. II. Changes due to magnesium ions concentration

Low-temperature (77K) steady-state chlorophyll fluorescence emission spectra, room temperature fluorescence and light scattering of thylakoid membranes isolated from pea mutants were studied as a function of Mg2+ concentration. The mutants have modified pigment content and altered structural organization of the pigment-protein complexes, distinct surface electric properties and functions. The analysis of the 77K emission spectra revealed that Mg2+-depletion of the medium caused not only an increased energy flow toward photosystem I in all investigated membranes but also changes in the quenching of the fluorescence, most probably by internal conversion. The results indicated that the macroorganization of the photosynthetic apparatus of mutants at supramolecular level (distribution and segregation of two photosystems in thylakoid membranes) and at supermolecular level (stacking of photosystem II supercomplexes) required different Mg ion concentrations. The data confirmed that the segregation of photosystems and the stacking of thylakoid membranes are two distinct phenomena and elucidated some features of their mechanisms. The segregation is initiated by changes in the lateral microorganization of light harvesting complexes II, their migration (repulsion from photosystem I) and subsequent separation of the two photosystems. Most likely 3D aggregation and formation of macrodomains, containing only photosystem II antenna complexes, play a certain precursory role for the increasing degree of the membrane stacking and the energy coupling between the light harvesting complexes II and the core complexes of photosystem II in the frame of photosystem II supercomplexes.     

Afterglow thermoluminescence measured in isolated chloroplasts

The thermoluminescence afterglow (AG) measured in plant leaves originates from the S(2)/S(3)Q(B)(-) charge pair recombination in photosystem II (PSII) initiated by reverse electron flow from stromal reductants to PQ and then to the Q(B) site in PSII centers that are in the S(2)/S(3)Q(B) state. In this study, we show that this luminescence, absent in isolated thylakoid membranes, can be measured in intact chloroplasts that retain their stromal content including the electron acceptor pool (oxidized ferredoxin/NADP(+)) of photosystem I. The properties of the chloroplasts AG emission is similar to the AG in leaves in terms of temperature maximum, period-four modulation, far-red light stimulation, and antimycin A inhibition.     

ISOTHERMAL LUMINESCENCE AND THERMO-LUMINESCENCE OF NUCLEIC ACID BASES FOLLOWING γ-IRRADIATION

Abstract— The emission spectra of radiation induced isothermal luminescence (ITL) and the thermolu-minescence (TL) of purines and pyrimidines of nucleic acids and analogue 6-azauracil in the form of pellets of dry polycrystalline powders have been studied at 77 K, and compared with their low temperature fluorescence and phosphorescence spectra. The qualitative and quantitative measurements of isothermal luminescence and thermoluminescence show that the two result from the same radiative transitions. The thermoluminescence emission was observed to coincide with the phosphorescence emission of the compounds in all the cases. The thermoluminescence of the pyrimidines and their analogue, however, have shown an additional component corresponding to their fluorescence in the ultraviolet region. An extension of the Weissbluth model based on the location of the electron traps in relation to the excited states of the compounds is proposed to explain their thermoluminescence emission.     

Characterization of the Photosynthetic Activity of Platinized Chloroplasts: A Study Using Fluorescence and Photoacoustic Techniques

In this report, the effect of platinization on the photosynthetic activity of the chloroplast membranes is studied. Oxygen evolution, fluorescence emission and thermal de-activation processes are modified after platinization. It is shown that photosystem II activity is affected by the hydrogen purging involved in the platinization procedure as seen by the reduced rates of oxygen evolution and a decrease in variable fluorescence. Depletion of bicarbonate from photosystem II during purging is suggested to be responsible partly for the decreased electron transfer rates and for a lower half-saturation light intensity required for energy storage as measured by photoacoustic spectroscopy. On the other hand, the electron sink created by the reduction of hydrogen at the acceptor side of photosystem I is shown to reoxidize efficiently the plas-toquinone pool of photosystem II.     

Carotenoid radical cations as a probe for the molecular mechanism of nonphotochemical quenching in oxygenic photosynthesis

Nonphotochemical quenching (NPQ) is a fundamental mechanism in photosynthesis which protects plants against excess excitation energy and is of crucial importance for their survival and fitness. Recently, carotenoid radical cation (Car*+) formation has been discovered to be a key step for the feedback deexcitation quenching mechanism (qE), a component of NPQ, of which the molecular mechanism and location is still unknown. We have generated and characterized carotenoid radical cations by means of resonant two color, two photon ionization (R2C2PI) spectroscopy. The Car*+ bands have maxima located at 830 nm (violaxanthin), 880 nm (lutein), 900 nm (zeaxanthin), and 920 nm (beta-carotene). The positions of these maxima depend strongly on solution conditions, the number of conjugated C=C bonds, and molecular structure. Furthermore, R2C2PI measurements on the light-harvesting complex of photosystem II (LHC II) samples with or without zeaxanthin (Zea) reveal the violaxanthin (Vio) radical cation (Vio*+) band at 909 nm and the Zea*+ band at 983 nm. The replacement of Vio by Zea in the light-harvesting complex II (LHC II) has no influence on the Chl excitation lifetime, and by exciting the Chls lowest excited state, no additional rise and decay corresponding to the Car*+ signal observed previously during qE was detected in the spectral range investigated (800-1050 nm). On the basis of our findings, the mechanism of qE involving the simple replacement of Vio with Zea in LHC II needs to be reconsidered.     

Luminescence quenching of tris(2,2'-bipyridine)ruthenium(II) by 2,6-dimethylphenol and 4-bromo-2,6-dimethylphenol in sol-gel-processed silicate thin films

The luminescence properties of tris(1,2-bipyridine)ruthenium(II) (Ru(bpy)(3)(2+)), included in different organically modified silicate gel matrixes were investigated. Spin and dip-coated thin films were prepared from methyltrimethoxysilane (MTMOS) and methyltriethoxysilane (MTEOS). A blue shift in the emission spectrum of the MLCT excited state of Ru(bpy)(3)(2+) with respect to the aqueous solution was observed in all the films, practically independent of the reaction pH used to prepare the "sol," silane-derived precursor, and procedure used (dip-coating or spin-coating) to obtain the film. A bimodal distribution of probe sites in the films was obtained from modeling of the emission decays by a double exponential and from application of the exponential series method. The parameters of the decay components depended principally on the thermal treatment used in the processing of the films. The lifetimes decreased with the increase in the drying temperature of the films; at the same time, the emission spectra showed a red shift and the luminescence efficiency decreased. A luminescence quenching of the ruthenium complex in the films by 4-bromo-2,6-dimethylphenol and 2,6-dimethylphenol in aerated aqueous solution at pH 12 in contact with the film was also observed. The quenching plots obtained from luminescence intensities or luminescence intensity decay measurements showed a downward curvature. These plots could be fitted satisfactorily by a sum of two Stern-Volmer terms with quenching constants K(SV1) and K(SV2) associated with two different binding sites of the ruthenium complex. This result is indicative of the matrix microheterogeneity in the films and is fully consistent with the biexponential nature of the luminescence intensity decay profiles. The Stern-Volmer parameter values for both sites in the films suggest that only a low percentage of the probe is accessible to the quencher and its respective constant K(SV1) is lower than in water.     

Photosystem II fluorescence lifetime imaging in avocado leaves: contributions of the lutein-epoxide and violaxanthin cycles to fluorescence quenching

Lifetime-resolved imaging measurements of chlorophyll a fluorescence were made on leaves of avocado plants to study whether rapidly reversible ΔpH-dependent (transthylakoid H(+) concentration gradient) thermal energy dissipation (qE) and slowly reversible ΔpH-independent fluorescence quenching (qI) are modulated by lutein-epoxide and violaxanthin cycles operating in parallel. Under normal conditions (without inhibitors), analysis of the chlorophyll a fluorescence lifetime data revealed two major lifetime pools (1.5 and 0.5 ns) for photosystem II during the ΔpH build-up under illumination. Formation of the 0.5-ns pool upon illumination was correlated with dark-retention of antheraxanthin and photo-converted lutein in leaves. Interconversion between the 1.5- and 0.5-ns lifetime pools took place during the slow part of the chlorophyll a fluorescence transient: first from 1.5 ns to 0.5 ns in the P-to-S phase, then back from 0.5 ns to 1.5 ns in the S-to-M phase. When linear electron transport and the resulting ΔpH build-up were inhibited by treatment with 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), the major fluorescence intensity was due to a 2.2-ns lifetime pool with a minor faster contribution of approximately 0.7 ns. In the presence of DCMU, neither the intensity nor the lifetimes of fluorescence were affected by antheraxanthin and photo-converted lutein. Thus, we conclude that both antheraxanthin and photo-converted lutein are able to enhance ΔpH-dependent qE processes that are associated with the 0.5-ns lifetime pool. However, unlike zeaxanthin, retention of antheraxanthin and photo-converted lutein may not by itself stabilize quenching or cause qI.     

Temperature-dependent energy gap of the primary charge separation in photosystem I: study of delayed fluorescence at 77-268 K

The dynamics of fluorescence decay and charge recombination were studied in the ether-extracted photosystem I reaction center isolated from spinach with picosecond resolution over a wide time range up to 100 ns. At all temperatures from 268 to 77 K, a slow fluorescence decay component with a 30-40 ns lifetime was detected. This component was interpreted as a delayed fluorescence emitted from the singlet excited state of the primary donor P700*, which is repopulated through charge recombination that was increased by the lack of secondary acceptor phylloquinone in the sample. Analysis of the fluorescence kinetics allowed estimation of the standard free-energy difference -DeltaG between P700* and the primary radical pair (P700(+)A0(-)) state over a wide temperature range. The values of -DeltaG were estimated to be 160/36 meV at 268/77 K, indicating its high sensitivity to temperature. A temperature-dependent -DeltaG value was also estimated in the delayed fluorescence of the isolated photosystem I in which the secondary acceptor quinone was partially prereduced by preillumination in the presence of dithionite. The results revealed that the temperature-dependent -DeltaG is a universal phenomenon common with the purple bacterial reaction centers, photosystem II and photosystem I reaction centers.     

Relationship between the structural and functional changes of the photosynthetic apparatus during chloroplast-chromoplast transition in flower bud of Lilium longiflorum

The relationship between the structural and functional changes of the photosynthetic apparatus in the flower bud of Lilium longiflorum during chloroplast-chromoplast transition was examined. Compared with green petals, there was a five-fold increase of the carotenoid content in yellow petals, whereas the chlorophyll content decreased five-fold. Absorption and emission fluorescence spectra of chromoplasts indicated that newly synthesized carotenoids were not associated with photosystem II (PSII) photochemistry. The maximum quantum yield in the remaining PSII reaction centers remained constant during the chromoplast formation, whereas the photosynthetic electron transport beyond PSII became inhibited, as indicated by a marked decrease of the O2 evolution capacity, of the photochemical quenching of chlorophyll-alpha fluorescence and of the operational quantum yield of photosynthetic electron transport. Deconvoluted fluorescence emission spectra indicated a more rapid degradation of photosystem I (PSI) complexes than of PSII during chromoplast formation. Compared with green petals, the spillover between PSII and PSI decreased by approximately 40% in yellow petals. Our results indicate that during chloroplast-chromoplast transition in the flower bud of L. longiflorum, PSII integrity was preserved longer than the rest of the photosynthetic apparatus.     

Effects of light on the photosynthetic apparatus and a novel type of degradation of the photosystem I peripheral antenna complexes under darkness

A novel type of degradation of photosystem I peripheral antenna complexes has been observed in rice leaves under darkness in the present study. Photosynthesis, chlorophyll content, the chlorophyll a/b ratio, and relative amounts of ribulose-1,5-bisphosphate carboxylase/oxygenase decrease during dark treatment. The levels of photosystem II reaction-center complex and cytochrome f on the basis of units of chlorophyll also decline rapidly under darkness. In contrast, the levels of photosystem I reaction-center complex remain stable under darkness for six days. Low-temperature fluorescence emission spectra ascribed to photosystem I antennae clearly show a blue shift. A similar shift is also observed in the photosystem I complexes resolved with dodecyl maltoside-polyacrylamide gel electrophoresis. Moreover, polypeptide analysis of the thylakoids and photosystem I complexes isolated from the green gels shows that some polypeptides originating from photosystem I peripheral antenna complexes disappear during the dark treatment. A curve-fitting method also displays remarkable changes in the chlorophyll components between the light and dark treatments. It is likely that these results indicate the disconnection/disassembly of the photosystem I antenna as well as the photosystem II complexes induced by dark treatment. Moreover, these findings also imply the existence of different degradation mechanisms for the photosystem I and II complexes.