Functional and structural organization of chlorophyll in the developing photosynthetic membranes of Euglena gracilis Z. II. Formation of system II photosynthetic units during greening under optimal light intensity.

The relationships between light-harvesting chlorophyll and reaction centers in Photosystem II were analyzed during the chloroplast development of dark-grown, non-dividing Euglena gracilis Z. Comparative measurements included light saturation of photosynthesis, oxygen evolution under flashing-light and fluorescence induction. The results obtained can be summarized as follows: (1) Photosystem II photocenters are formed in parallel with chlorophyll synthesis, but after a long lag phase. (2) As a consequence, the chlorophyll reaction center ratio (Emerson's type photosynthetic unit) decreases during greening. (3) This decrease is accompanied by considerable changes in the energy transfer and trapping properties of Photosystem II. Most of the initially synthesized chlorophylls are inactive in the transfer of excitations to active photochemical centers and are shared among newly formed Photosystem II photocenters; as a consequence, the number of chlorophylls functionally connected to each Photosystem II photocenter decreases and cooperatively between these centers appears. Results are discussed in terms of chlorophyll organization in developing photosynthetic membranes with reference to the lake or puddle models of photosynthetic unit organization.     

Structure and organization of System II photosynthetic units during the greening of a dark-grown Chlorella mutant

The formation and the organization of Photosystem II photosynthetic units during the greening of a dark-grown Chlorella vulgaris, mutant 5/520, have been investigated by analysing the kinetics of the “activation” of oxygen evolution and of the fluorescence induction.

1. 1. The existence during the early stages of the greening of a stationary photosynthesis demonstrates the presence of active Photosystem II at these initial stages, which are integrated in a functional whole, leading to overall photosynthesis.

2. 2. The rise-time of oxygen evolution has been measured using far-red and green light in order to estimate the relative number of chlorophylls per unit. The amount of chlorophyll a remains relatively constant during the greening, while the progressive addition of chlorophyll b causes the size of the units to increase approx. 2-fold.

3. 3. The induction kinetics of the fluorescence are exponential during the early phases of greening and later become distinctly sigmoidal; this suggests that the first units synthesized on the surface of the membrane are isolated from each other by obstacles preventing electronic excitation transfers and that such obstacles which might correspond to some distance between such units, can disappear at later stages, allowing energy transfers to occur.

These observations suggest that the Photosystem II units represent organized functional entities. They apparently consist of a relatively constant number of chlorophyll a molecules, which during the greening is complemented progressively by the addition of chlorophyll b.     

Energy transfers from Photosystem II to Photosystem I in Cryptomonas rufescens (Cryptophyceae)

In Cryptomonas rufescens (Cryptophyceae), phycoerythrin located in the thylakoid lumen is the major accessory pigment. Oxygen action spectra prove phycoerythrin to be efficient in trapping light energy.The fluorescence excitation spectra at ?196°C obtained by the method of Butler and Kitajima (Butler, W.L. and Kitajima, M. (1975) Biochim. Biophys. Acta 396, 72–85) indicate that like in Rhodophycease, chlorophyll a is the exclusive light-harvesting pigment for Photosystem I.For Photosystem II we can observe two types of antennae: (1) a light-harvesting chlorophyll complex connected to Photosystem II reaction centers, which transfers excitation energy to Photosystem I reaction centers when all the Photosystem II traps are closed. (2) A light-harvesting phycoerythrin complex, which transfers excitation energy exclusively to the Photosystem II reaction complexes responsible for fluorescence at 690 nm.We conclude that in Cryptophyceae, phycoerythrin is an efficient light-harvesting pigment, organized as an antenna connected to Photosystem II centers, antenna situated in the lumen of the thylakoid. However, we cannot afford to exclude that a few parts of phycobilin pigments could be connected to inactive chlorophylls fluorescing at 690 nm.     

Photoinhibition of Reaction Centers of Photosystems I and II in Intact Bryopsis Chloroplasts under Anaerobic Conditions

Illumination of intact Bryopsis corticulans chloroplasts under anaerobic conditions induced a decline of chlorophyll fluorescence and photoinhibition of Photosystems I and II. The time course of the light-induced decline of chlorophyll fluorescence and the decreases of activities of reactions sensitized by Photosystems I and II were compared. Photosystem I activity decreased in parallel with the disappearance of active P700. The time course of the destruction of the reaction center of Photosystem II was similar to that of photoinhibition of 2,6-dichlorophenolindophenol-Hill reaction.

It appears that the initial events in photoinhibition are the destruction of the reaction centers of Photosystems I and II and that the reaction centers that are inhibited become quenchers of chlorophyll fluorescence.

Effects of inhibitors of electron transfer and of an electron donor to Photosystem I showed that photoinhibition was related to Photosystem I activity.

     

The relative absorption cross-sections of Photosystem I and Photosystem II in chloroplasts from three types of Nicotiana tabacum

In the present study we used three types of Nicotiana tabacum, cv John William's Broad Leaf (the wild type and two mutants, the yellow-green Su/su and the yellow Su/su var. Aurea) in order to correlate functional properties of Photosystem II and Photosystem I with the structural organization of their chloroplasts. The effective absorption cross-section of Photosystem II and Photosystem I centers was measured by means of the rate constant of their photoconversion under light-limiting conditions. In agreement with earlier results (Okabe, K., Schmid, G.H. and Straub, J. (1977) Plant Physiol. 60, 150–156) the photosynthetic unit size for both System II and System I in the two mutants was considerably smaller as compared to the wild type. We observed biphasic kinetics in the photoconversion of System II in all three types of N. tabacum. However, the photoconversion of System I occurred with monophasic and exponential kinetics. Under our experimental conditions, the effective cross-section of Photosystem I was comparable to that of the fast System II component (α centers). The relative amplitude of the slow System II component (β centers) varied between 30% in the wild type to 70% in the Su/su var. Aurea mutant. The increased fraction of β centers is correlated with the decreased fraction of appressed photosynthetic membranes in the chloroplasts of the two mutants. As a working hypothesis, it is suggested that β centers are located on photosynthetic membranes directly exposed to the stroma medium.     

Effects of growth irradiance levels on the ratio of reaction centers in two species of marine phytoplankton

Cells of two species of single-celled marine algae, the diatom Skeletonema costatum (Greve), Cleve, and the chlorophyte Dunaliella tertiolecta Butcher, were cultured in white light of high (500-600 microeinsteins per square meter per second) and low (30 microeinsteins per square meter per second) intensity. For both algal species, cells grown at low light levels contained more chlorophyll a and had a lower ratio of chlorophyll a to chlorophylls b or c than did cells grown at high light levels. When photosynthetic unit sizes were measured on the basis of either oxygen flash yields or P₇₀₀ photooxidation, different results were obtained with the different species. In the chlorophyte, the cellular content of photosystem I (PSI) and photosystem II (PSII) reaction centers increased in tandem as chlorophyll a content increased so that photosynthetic unit sizes changed only slightly and the ratio PSI:PSII reaction centers remained constant at about 1.1. In the diatom, as the chlorophyll content of the cells increased, the number of PSI reaction centers decreased and the number of PSII reaction centers increased so that the ratio of PSI:PSII reaction centers decreased from about unity to 0.44. In neither organism did photosynthetic capacity correlate with changes in cellular content of PSI or PSII reaction centers. The results are discussed in relationship to the physical and biological significance of the photosynthetic unit concept.     

Effect of photosystem II reaction center closure on nanosecond fluorescence relaxation kinetics

The fluorescence decay of chlorophyll in spinach thylakoids was measured as a function of the degree of closure of Photosystem II reaction centers, which was set for the flowed sample by varying either the preillumination by actinic light or the exposure of the sample to the exciting pulsed laser light. Three exponential kinetic components originating in Photosystem II were fitted to the decays; a fourth component arising from Photosystem I was determined to be negligible at the emission wavelength of 685 nm at which the fluorescence decays were measured. Both the lifetimes and the amplitudes of the components vary with reaction center closure. A fast (170–330 ps) component reflects the trapping kinetics of open Photosystem II reaction centers capable of reducing the plastoquinone pool; its amplitude decreases gradually with trap closure, which is incompatible with the concept of photosynthetic unit connectivity where excitation energy which encounters a closed trap can find a different, possibly open one. For a connected system, the amplitude of the fast fluorescence component is expected to remain constant. The slow component (1.7–3.0 ns) is virtually absent when the reaction centers are open, and its growth is attributable to the appearance of closed centers. The middle component (0.4–1.7 ns) with approximately constant amplitude may originate from centers that are not functionally linked to the plastoquinone pool. To explain the continuous increase in the lifetimes of all three components upon reaction center closure, we propose that the transmembrane electric field generated by photosynthetic turnover modulates the trapping kinetics in Photosystem II and thereby affects the excited state lifetime in the antenna in the trap-limited case.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - HEPES 4-(2-hydroxyethyl)-1-piperazineethane sulfonic acid - PQ plastoquinone - PSI and PSII Photosystem I and II - Q_A and Q_B primary and secondary quinone acceptor of PSII     

Pigment protein complexes and the concept of the photosynthetic unit: Chlorophyll complexes and phycobilisomes

The photosynthetic unit includes the reaction centers (RC 1 and RC 2) and the light-harvesting complexes which contribute to evolution of one O₂ molecule. The light-harvesting complexes, that greatly expand the absorptance capacity of the reactions, have evolved along three principal lines. First, in green plants distinct chlorophyll (Chl) a/b-binding intrinsic membrane complexes are associated with RC 1 and RC 2. The Chl a/b-binding complexes may add about 200 additional chromophores to RC 2. Second, cyanobacteria and red algae have a significant type of antenna (with RC 2) in the form of phycobilisomes. A phycobilisome, depending on the size and phycobiliprotein composition adds from 700 to 2300 light-absorbing chromophores. Red algae also have a sizable Chl a-binding complex associated with RC 1, contributing an additional 70 chromophores. Third, in chromophytes a variety of carotenoid-Chl-complexes are found. Some are found associated with RC 1 where they may greatly enhance the absorptance capacity. Association of complexes with RC 2 has been more difficult to ascertain, but is also expected in chromophytes. The apoprotein framework of the complexes provides specific chromophore attachment sites, which assures a directional energy transfer whithin complexes and between complexes and reaction centers. The major Chl-binding antenna proteins generally have a size of 16–28 kDa, whether of chlorophytes, chromophytes, or rhodophytes. High sequence homology observed in two of three transmembrane regions, and in putative chlorophyll-binding residues, suggests that the complexes are related and probably did not evolve from widely divergent polyphyletic lines.Abbreviations APC allophycocyanin - B phycoerythrin-large bangiophycean phycoerythrin - Chl chlorophyll - L_CM linker polypeptide in phycobilisome to thylakoid - FCP fucoxanthin Chl a/c complex - LHC(s) Chl-binding light harvesting complex(s) - LHC I Chl-binding complex of Photosystem I - LHC II Chl-binding complex of Photosystem II - PC phycocyanin - PCP peridinin Chl-binding complex - P700 photochemically active Chl a of Photosystem I - PS I Photosystem I - PS II Photosystem II - RC 1 reaction center core of PS I - RC 2 reaction center core of PS II - R phycoerythrin-large rhodophycean phycoerythrin - sPCP soluble peridinin Chl-binding complex     

Energy transfer in the photochemical apparatus of flashed bean leaves

Fluorescence and energy transfer properties of bean leaves greened by brief, repetitive xenon flashes were studied at −196 °C. The bleaching of P-700 has no influence on the yield of fluorescence at any wavelength of emission. The light-induced fluorescence yield changes which are observed in both the 690 and 730 nm emission bands in the low temperature fluorescence spectra are due to changes in the state of the Photosystem II reaction centers. The fluorescence yield changes in the 730 nm band are attributed to energy transfer from Photosystem II to Photosystem I. Such energy transfer was also confirmed by measurements of the rate of photooxidation of P-700 at −196 °C in leaves in which the Photosystem II reaction centers were either all open or all closed. It is concluded that energy transfer from Photosystem II to Photosystem I occurs in the flashed bean leaves which lack the light-harvesting chlorophyll a/b protein.     

Formation of photosynthetic pigments and quinones and development of photosynthetic activity in barley etioplasts during greening in intermittent and continuous white light

The appearance and development of photosynthetic activity, and the accumulation of chlorophylls, carotenoids and quinones, was investigated in etiolated barley shoots (Hordeum vulgare L. cv. Villa) during greening in flash light, periodic light-dark cycles, and continuous white light. Greening and the development of photosynthetic activity was delayed in flash and periodic light compared to continuous white light. Photosystem II activity occurred after 6 light-dark cycles and increased continuously during greening. After 3 h greening in continuous white light, photosystem II activity appeared with a very high rate and decreased to that of a green leaf after 50 h greening. Parallel to the development of photosynthetic activity, light stimulated the biosynthesis of prenyllipids. Moreover, chlorophylls and those carotenoids and quinones that are contained in etioplasts in relatively small amounts, were particularly enhanced in their biosynthesis. Chlorophyll a was synthesized without a lag phase during greening in flash light, whereas a 2 h lag phase occurred in continuous white light. In all three modes of illumination the formation of chlorophyll a exceeded that of chlorophyll b. After 4 flashes and 2 light-dark cycles, chlorophyll b could be detected with a very high initial a/b ratio. Higher chlorophyll a/b ratios were reached after 200 flashes (a/b=10.9) and 50 light-dark cycles (a/b=6.6) than after 50 h continuous white light (a/b=3.3). The formation of carotenes, lutein, violaxanthin and neoxanthin was also enhanced by light. This was also confirmed for plast-ouinone-9. ?-tocopherol,α-tocoquinone and phylloquinone. A comparison of the carotenoid and quinone composition of the differentiating thylakoid membrane before and after onset of photosynthesis, reveals that the photosynthetic membrane is already equipped with photosynthetic pigments and quinones before the appearance of photosystem II activity. It is concluded that during development of the photo-synthetic apparatus the thylakoid membrane with its structural and functional constituents is formed first. In a second and slower process the water splitting enzyme system and enzymes of the Calvin cycle are activated.     

Functional Organization of the Chlorophyll-Containing Complexes of Chlamydomonas reinhardi: A Study of Their Formation and Interconnection with Reaction Centers in the Greening Process of the y-1 Mutant

The stepwise synthesis and assembly of photosynthetic membrane components in the y-1 mutant of Chlamydomonas reinhardi have been previously demonstrated (Ohad 1975 In Membrane Biogenesis, Mitochondria, Chloroplasts and Bacteria, Plenum, pp 279-350). This experimental system was used here in order to investigate the process of formation and interconnection of the energy collecting chlorophylls with the reaction centers of both photosystems I and II. The following measurements were carried out: photosynthetic electron flow at various light intensities, including parts or the entire electron transfer chain; analysis of the kinetics of fluorescence emission at room temperature and fluorescence emission spectra at 77 K, and electrophoretic separation of membrane polypeptides and chlorophyll protein complexes. Based on the data obtained it is concluded that: (a) each photosystem (PSI and PSII) contains, in addition to the reaction center, an interconnecting antenna and a main or light harvesting antenna complex; (b) the formation of the light harvesting complex, interconnecting antenna, and reaction centers for each photosystem can occur independently. (c) the interconnecting antennae link the light harvesting complexes with the respective reaction centers. In their absence, energy transfer between the light harvesting chlorophylls and the reaction centers is inefficient. The formation of the interconnecting antennae and efficient assembly of photosystem components occur simultaneously with the de novo synthesis of chlorophyll and at least three polypeptides, one translated in the cytoplasm and two translated in the chloroplast. The synthesis of these polypeptides was found to be light dependent.     

Modeling of primary photosynthetic processes using the kinetic Monte Carlo method

Processes that occur in the ensemble of photosynthetic electron transport systems have been modeled using a kinetic Monte Carlo method. The size of a simulated ensemble (3–5 million elementary photosynthetic chains) corresponds to the number of photosynthetic reaction centers in a plant cell. The method enables one to modify the structure of a model system according to different concepts of the organization of processes in a photosynthetic membrane. Using this model, the experimental kinetics of the chlorophyll fluorescence induction associated with the Photosystem II and the redox transformations of a photoactive pigment of the Photosystem I have been successfully reproduced. The model was verified by comparing the calculated fluorescence induction curves to experimental curves, obtained in the presence of various photosynthesis inhibitors and under temperature inactivation of the Photosystem II donor side.     

Development of the Primary Photochemical Apparatus of Photosynthesis during Greening of Etiolated Bean Leaves

Seven-day-old dark-grown bean leaves were greened under continuous light. The amount of chlorophyll, the ratio of chlorophyll a to chlorophyll b, the O₂ evolving capacity and the primary photochemical activities of Photosystem I and Photosystem II were measured on the leaves after various times of greening. The primary photochemical activities were measured as the photo-oxidation of P₇₀₀, the photoreduction of C-550, and the photo-oxidation of cytochrome b₅₅₉ in intact leaves frozen to −196 C. The results indicate that the reaction centers of Photosystem I and Photosystem II begin to appear within the first few minutes and that Photosystem II reaction centers accumulate more rapidly than Photosystem I reaction centers during the first few hours of greening. The very early appearances of the primary photochemical activity of Photosystem II was also confirmed by light-induced fluorescence yield measurements at −196 C.     

Energy transfer in a model of the photosynthetic unit of green plants

A model array is set up to represent a photosynthetic unit of 344 chlorophyll molecules of seven different spectral varieties and in definite orientations. The array is provided with two traps, representing the reaction centers of photosystems I and II. The number of jumps required to obtain a high probability of trapping is lower than on a similar array of undifferentiated chlorophylls by a factor of 15. Most of the molecules fall into two groups which transfer their energy predominantly into one or the other trap, and which may be regarded as functional photosystems I and II. The rate of transfer between these two functional photosystems can be controlled by redirecting the orientation of only six of the molecules, which occupy a key position in the array. The effect on trapping rates of reorientation of these molecules is especially pronounced when one of the traps is closed. This constitutes a model for the control of energy distribution between the two photosystems, as indicated in recent years through fluorescence studies.     

The photochemical and fluorescence properties of whole cells,spheroplasts and spheroplast particles from the blue-green alga Phormidium luridum

The photochemical activities and fluorescence properties of cells, spheroplasts and spheroplast particles from the blue-green alga Phormidium luridum were compared. The photochemical activities were measured in a whole range of wavelengths and expressed as quantum yield spectra (quantum yield vs. wavelength). The following reactions were measured: Photosynthesis (O₂ evolution) in whole cells; Hill reaction (O₂ evolution) with Fe(CN)₆^3? and NADP as electron acceptors (Photosystem II and Photosystem II+Photosystem I reactions); electron transfer from reduced 2,6-dichlorophenolindophenol to diquat (Photosystem I reaction). The fluorescence properties were emission spectra, quantum yield spectra and the induction pattern.On the basis of comparison between the quantum yield spectra and the pigments compositions the relative contribution of each pigment to each photosystem was estimated. In normal cells and spheroplasts it was found that Photosystem I (Photosystem II) contains about 90 % (10 %) of the chlorophyll a, 90 % (10 %) of the carotenoids and 15 % (85 %) of the phycocyanin. In spheroplast particles there is a reorganization of the pigments: they loose a certain fraction (about half) of the phycocyanin but the remaining phycocyanin attaches itself exclusively to Photosystem I (!). This is reflected by the loss of Photosystem II activity, a flat quantum yield vs. wavelength dependence and a loss of the fluorescence induction.The fluorescence quantum yield spectra conform qualitatively to the above conclusion. More quantitative estimation shows that only a fraction (20–40 %) of the chlorophyll of Photosystem II is fluorescent. Total emission spectrum and the ratio of variable to constant fluorescence are in agreement with this conclusion.The fluorescence emission spectrum shows characteristic differences between the constant and variable components. The variable fluorescence comes exclusively from chlorophyll a; the constant fluorescence is contributed, in addition to chlorophyll a, by phycocyanine and an unidentified long wavelength component.The variable fluorescence does not change in the transition from whole cells to spheroplasts. However, the constant fluorescence increases considerably. This indicates the release of a small fraction of pigments from the photosynthetic photochemical apparatus which then become fluorescent.     

Changes in photosynthetic activity in the cyanobacterium Chlorogloea fritschii following transition from dark to light growth

The cyanobacterium Chlorogloea fritschii loses Photosystem II activity, measured by delayed fluorescence and oxygen evolution, during dark heterotrophic growth, but retains Photosystem I, measured as light induced EPR signals. Following transition to the light, Photosystem II recovers in two stages, the first of which does not require protein synthesis. New Photosystem I reaction centres are not synthesised until after net chlorophyll synthesis has commenced. Carbon dioxide fixation recovery commences immediately, the initial rate being unaffected by chloramphenicol. The recovery of carbon dioxide fixation is not directly related to oxygen evolution rate and is only inhibited slightly by 3-(3,4-dichlorophyenyl)-1,1-dimethylurea and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone.     

Limitations for finding a linear relationship between chlorophyll content and photosynthetic activity

In experiments with fodder cabbage and sugar beet the influences were tested which restrict the finding of a uniform linear dependence between the chlorophyll content and photosynthetic rate. The main factor is most probably the irradiation during the growth of plants and the measuring of photosynthetic rate. Changes in the density and length of irradiation with the proceeding spring season are reflected in the decrease of unit chlorophyll activity in all leaves of the plant. Such differences were not observed in plants grown in winter months at a low greenhouse irradiation density. High irradiation density during the measurement of photosynthesis ensures the finding of high correlation of photosynthetic rate with the chlorophyll amount per unit area of leaf. With a low irradiation density, or in thick leaves, the lower layers of chloroplasts are not saturated with radiation, and hence a higher correlation coefficient is found by relating photosynthetic rate to the percentage of chlorophyll in dry weight than to the quantity of chlorophyll per unit area of leaf blade. In some experiments higher activity of chlorophylls was found in young leaves before they have reached the state of “photosynthetic maturity” than after this turning point. This difference diminished by relating the photosynthetic rate to chlorophylla content instead of the total amount of chlorophylls (a+b). High activity of chlorophylls in very young leaves and great individual variability within the experimental plant groups caused by uneven cultivation conditions are the basis of apparent sigmoid character of average curves for the chlorophyll-photosynthesis relation.     

Functional and structural organization of chlorophyll in the developing photosynthetic membranes of Euglena gracilis Z. IV. Light-harvesting properties of system II photosynthetic units and thylakoid ultrastructure during greening under intermittent light

Dark-grown, non-dividing Euglena gracilis Z cells were exposed for 100 h to intermittent light (15 s every 15 min darkness) and were then transferred to continuous light. During chloroplast differentiation, the development of light harvesting and trapping properties of Photosystem II was analyzed mainly with fluorescence induction measurements in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea and was associated with observations on ultrastructural organisation of developing thylakoids using thin section and freeze-fracture methods. Results showed that: (a) the synthesis of chlorophyll b and probably that of the light-harvesting chlorophyll a/b-protein complex was more reduced by intermittent light than the formation of active system II reaction centers; (b) the size of the overall photosynthetic units, i.e. the number of chlorophyll molecules per O2 molecule evolved under a regime of repetitive saturating short flashes were reduced by 2-3 compared to those developed under continuous light; (c) the lack of chlorophyll induced by intermittent light affected more specifically the size of light-harvesting antennae of system II units, the optical cross-section of which was reduced by 3-4; (d) energy transfers did not occur between these small system II units in spite of high concentrations of PS II reaction centers and of a high trapping efficiency of the absorbed energy; (e) thylakoids developed under intermittent light were not stacked; (f) particles on exoplasmic fracture faces were significantly smaller than those developed under continuous light; (g) rapid synthesis of chlorophyll (Chl a and Chl b) upon exposure to continuous light of cells first greened under intermittent light are concomittant with rapid recovery of light-harvesting properties and structural characteristics of thylakoids developed under continuous light. These structural and functional observations are consistent with the hypothesis that system II units are organized in the photosynthetic membrane as individual and discrete entities, the morphological expression of which correspond to exoplasmic fracture face particles. They also support the model whereby energy transfers between physically connected system II units could occur across the partition between exoplasmic fracture face particles brought into contact in stacked regions.     

Organization of the photosynthetic apparatus of the chlorina-f2 mutant of barley using chlorophyll fluorescence decay kinetics

The time-resolved chlorophyll fluorescence emission of higher plant chloroplasts monitors the primary processes of photosynthesis and reflects photosynthetic membrane organization. In the present study we compare measurements of the chlorophyll fluorescence decay kinetics of the chlorophyll-b-less chlorina-f2 barley mutant and wild-type barley to investigate the effect of alterations in thylakoid membrane composition on chlorophyll fluorescence. Our analysis characterizes the fluorescence decay of chlorina-f2 barley chloroplasts by three exponential components with lifetimes of approx. 100 ps, 400 ps and 2 ns. The majority of the chlorophyll fluorescence originates in the two faster decay components. Although photo-induced and cation-induced effects on fluorescence yields are evident, the fluorescence lifetimes are independent of the state of the Photosystem-II reaction centers and the degree of grana stacking. Wild-type barley chloroplasts also exhibit three kinetic fluorescence components, but they are distinguished from those of the chlorina-f2 chloroplasts by a slow decay component which displays cation- and photo-induced yield and lifetime changes. A comparison is presented of the kinetic analysis of the chlorina-f2 barley fluorescence to the decay kinetics previously measured for intermittent-light-grown peas (Karukstis, K. and Sauer, K. (1983) Biochim. Biophys. Acta 725, 384–393). We propose that similarities in the fluorescence decay kinetics of both species are a consequence of analogous rearrangements of the thylakoid membrane organization due to the deficiencies present in the light-harvesting chlorophyll $\text{a}\text{b}$ complex.     

Reaction center and antenna processes in photosynthesis at low temperature

Around 1960 experiments of Arnold and Clayton, Chance and Nishimura and Calvin and coworkers demonstrated that the primary photosynthetic electron transfer processes are not abolished by cooling to cryogenic temperatures. After a brief historical introduction, this review discusses some aspects of electron transfer in bacterial reaction centers and of optical spectroscopy of photosynthetic systems with emphasis on low-temperature experiments.Abbreviations (B)Chl (bacterio)chlorophyll - (B)Phe (bacterio)pheophytin - FMO Fenna-Matthews-Olson - LH1, LH2 light harvesting complexes of purple bacteria - LHC II, CP47 light harvesting complexes of Photosystem II - P, P870 primary electron donor - RC reaction center