Cobalt chloride induced stimulation of Photosystem II electron transport in Synechocystis sp. PCC 6803 cells

Synechocystis sp. PCC 6803 when grown in the presence of sublethal (M) levels of cobalt chloride shows an enhancement of Photosystem II (PS II) catalyzed Hill reaction. This stimulation seems to be induced by cobalt ions as other metal ions inhibit para-benzoquinone catalyzed Hill reaction. At saturating white light intensity, this enhancement is two times over that of the control cells on unit chlorophyll basis. Analysis of the PS II electron transport rate at varying intensities of white, blue or yellow light suggests an increased maximal rates but no change in the quantum yield or effective antenna size of CoCl₂-grown cells. There were no structural and functional changes in the phycobilisome as judged by the absence of changes in the phycocyanin/allophycocyanin ratio, fluorescence emission spectra, second derivative absorption spectra at 77 K and SDS-PAGE analysis of isolated phycobilisomes. The 77 K fluorescence emission spectra of the cells showed a decrease in the ratio of Photosystem I emission (F725) to Photosystem II emission (F685) in CoCl₂-grown cells compared to the control cells. These observations indicate three possibilities: (1) there is an increase in the number of Photosystem II units; (2) a faster turnover of Photosystem II centers; or (3) an alteration in energy redistribution between PS II and PS I in CoCl₂-grown cells which causes stimulation of Photosystem II electron transport rate.Abbreviations APC allophycocyanin - Chl a chlorophyll a - DBMIB 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone - EDTA ethylene diamine tetraacetic acid - PBS phycobilisome - PC phycocyanin - PSI Photosystem I - PS II Photosystem II - pBQ p-benzoquinone - PMSF phenyl methyl sulfonyl fluoride     

Changes in the antenna size of Photosystem I and Photosystem II in Synechococcus sp. strain PCC 7942 grown in the presence of SANDOZ 9785 — a Photosystem II inhibitor

SANDOZ 9785, also known as BASF 13.338, is a pyridazinone derivative that inhibits Photosystem II (PS II) activity leading to an imbalance in the rate of electron transport through the photosystems. Synechococcus sp. strain PCC 7942 cells grown in the presence of sublethal concentration of SANDOZ 9785 (SAN 9785) for 48 hours exhibited a 20% decrease in Chl a per cell. However, no changes were observed in the content of phycocyanin per cell, the size of the phycobilisomes or in the PS II:PS I ratio. From an estimate of PS II electron transport rate under varying light intensities and spectral qualities and analysis of room temperature Chl a fluorescence induction, it was deduced that growth of Synechococcus PCC 7942 in the presence of SAN 9785 leads to a redistribution of excitation energy in favour of PS II. Though the redistribution appears to be primarily caused by changes affecting the Chl a antenna of PS II, the extent of energetic coupling between phycobilisomes and PS II is also enhanced in SAN 9785 grown Synechococcus PCC 7942 cells. There was a reduction in the effective size of PS I antenna based on measurement of P700 photooxidation kinetics. These results indicate that when PS II is partially inhibited, the structure of photosynthetic apparatus alters to redistribute the excitation energy in favour of PS II so that the efficiency of utilization of light energy by the two photosystems is optimized. Our results suggest that under the conditions used, drastic structural changes are not essential for redistribution of excitation energy between the photosystems.Abbreviations APC Allophycocyanin - Chl a chlorophyll a - DBMIB 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone - DCMU 3-(3,4-dichlorophyenyl)-1,1-dimethyl urea - DCIP 2,6-dichlorophenolindophenol - F_o fluorescence when all the reaction centres are open - f_m fluorescence yield when all the reaction centres are closed - F_v variable chlorophyll fluorescence - HEPES N-2-Hydroxyethylpiperazine-N-2-ethanesulphonic Acid - I₅₀ concentration that causes 50% inhibition in activity - MV methyl viologen - pBQ para benzoquinone - PBS phycobilisome - PC phycocyanin - PS I, PS II Photosystem I, Photosystem II - P700 reaction centre Chl a of PS I - SAN 9785 SANDOZ 9785 i.e. 4-chloro-5-dimethylamino-2-phenyl-3 (2H) pyridazinone, also known as BASF 13.338     

Changes in the cyanobacterial photosynthetic apparatus during acclimation to macronutrient deprivation

When the cyanobacterium Synechococcus sp. Strain PCC 7942 is deprived of an essential macronutrient such as nitrogen, sulfur or phosphorus, cellular phycobiliprotein and chlorophyll contents decline. The level of -carotene declines proportionately to chlorophyll, but the level of zeaxanthin increases relative to chlorophyll. In nitrogen- or sulfur-deprived cells there is a net degradation of phycobiliproteins. Otherwise, the declines in cellular pigmentation are due largely to the diluting effect of continued cell division after new pigment synthesis ceases and not to net pigment degradation. There was also a rapid decrease in O₂ evolution when Synechococcus sp. Strain PCC 7942 was deprived of macronutrients. The rate of O₂ evolution declined by more than 90% in nitrogen- or sulfur-deprived cells, and by approximately 40% in phosphorus-deprived cells. In addition, in all three cases the fluorescence emissions from Photosystem II and its antennae were reduced relative to that of Photosystem I and the remaining phycobilisomes. Furthermore, state transitions were not observed in cells deprived of sulfur or nitrogen and were greatly reduced in cells deprived of phosphorus. Photoacoustic measurements of the energy storage capacity of photosynthesis also showed that Photosystem II activity declined in nutrient-deprived cells. In contrast, energy storage by Photosystem I was unaffected, suggesting that Photosystem I-driven cyclic electron flow persisted in nutrient-deprived cells. These results indicate that in the modified photosynthetic apparatus of nutrient-deprived cells, a much larger fraction of the photosynthetic activity is driven by Photosystem I than in nutrient-replete cells.Abbreviations ES energy storage - N nitrogen - P phosphorus - PBS phycobilisomes - S sulfur     

Fluorescence changes accompanying short-term light adaptations in photosystem I and photosystem II of the cyanobacterium <Emphasis Type="Italic">Synechocystis</Emphasis> sp. PCC 6803 and phycobiliprotein-impaired mutants: State 1/State 2 transitions and carotenoid-induced quenching of phycobilisomes

The features of the two types of short-term light-adaptations of photosynthetic apparatus, State 1/State 2 transitions, and non-photochemical fluorescence quenching of phycobilisomes (PBS) by orange carotene-protein (OCP) were compared in the cyanobacterium Synechocystis sp. PCC 6803 wild type, CK pigment mutant lacking phycocyanin, and PAL mutant totally devoid of phycobiliproteins. The permanent presence of PBS-specific peaks in the in situ action spectra of photosystem I (PSI) and photosystem II (PSII), as well as in the 77 K fluorescence excitation spectra for chlorophyll emission at 690 nm (PSII) and 725 nm (PSI) showed that PBS are constitutive antenna complexes of both photosystems. The mutant strains compensated the lack of phycobiliproteins by higher PSII content and by intensification of photosynthetic linear electron transfer. The detectable changes of energy migration from PBS to the PSI and PSII in the Synechocystis wild type and the CK mutant in State 1 and State 2 according to the fluorescence excitation spectra measurements were not registered. The constant level of fluorescence emission of PSI during State 1/State 2 transitions and simultaneous increase of chlorophyll fluorescence emission of PSII in State 1 in Synechocystis PAL mutant allowed to propose that spillover is an unlikely mechanism of state transitions. Blue–green light absorbed by OCP diminished the rout of energy from PBS to PSI while energy migration from PBS to PSII was less influenced. Therefore, the main role of OCP-induced quenching of PBS is the limitation of PSI activity and cyclic electron transport under relatively high light conditions.     

Effects of chlorophyll availability on phycobilisomes in Synechocystis sp. PCC 6803

Inactivation of the chlL gene in Synechocystis sp. PCC 6803 resulted in negligible chlorophyll content when the mutant was grown in darkness. Upon phycocyanin excitation at 580 nm, the 77K fluorescence spectrum of dark-grown cells showed three peaks at 648 nm, 665 nm, and 685 nm, this last being the largest. This reflects the functional presence of major components of phycobilisomes, including phycocyanin, allophycocyanin, and the terminal emitter, and efficient energy transfer between these components. As expected, no fluorescence emission peaks corresponding to chlorophyll in the photosystems were observed. Intact phycobilisomes could be isolated from the dark-grown chlL-deletion mutant. However, the phycobilisomes had a lower efficiency of energy transfer than did those isolated from the light-grown mutant, probably because of a decreased phycobilisome stability in the absence of chlorophyll. Exposing the dark-grown chlL-deletion mutant to light triggered the biosynthesis of chlorophyll. For the first 6 h in the light, upon phycocyanin excitation at 580 nm, the 77K fluorescence emission spectrum of greening cells was identical to that of dark-grown cells that lacked significant amounts of chlorophyll. With increased chlorophyll synthesis, gradual energy transfer from phycobilisomes to the two photosystems can be demonstrated.     

Selective disruption of energy flow from phycobilisomes to Photosystem I

Efficient production of ATP and NADPH by the light reactions of oxygen-evolving photosynthesis demands continuous adjustment of transfer of absorbed light energy from antenna complexes to Photosystem I (PS I) and II (PS II) reaction center complexes in response to changes in light quality. Treatment of intact cyanobacterial cells with N-ethylmaleimide appears to disrupt energy transfer from phycobilisomes to Photosystem I (PS I). Energy transfer from phycobilisomes to Photosystem II (PS II) is unperturbed. Spectroscopic analysis indicates that the individual complexes (phycobilisomes, PS II, PS I) remain functionally intact under these conditions. The results are consistent with the presence of connections between phycobiliproteins and both PS II and PS I, but they do not support the existence of direct contacts between the two photosystems.Abbreviations Chl chlorophyll - EPR electron paramagnetic resonance - NEM N-ethylmaleimide - PBS phycobilisome - PS photosystem     

Effect of Sodium Thiosulfate on the Depletion of Photosynthetic Apparatus in Cyanobacterium Synechocystis sp. PCC 6803 Cells Grown in the Presence of Glucose

Fluorescence spectroscopy at 77 K showed that the application of glucose lead to the depletion of phycobilisomes (PBS) and photosystems (PS) 2 and 1, and that PS2 was more sensitive to glucose than PS1. The application of sodium thiosulfate, an effective scavenger of reactive oxygen intermediates, counteracted the effects of glucose. Sodium thiosulfate effectively protected photosynthetic apparatus, PS2, PS1, and PBS against glucose-induced depletion. Sodium thiosulfate showed strong capability to inhibit the disappearance of chlorophyll induced by glucose. At a relatively low concentration of glucose, the application of sodium thiosulfate can even be helpful for the assembly of photosynthetic apparatus. Hence the reactive oxygen species might be involved in the depletion of the photosynthetic apparatus in the cyanobacterium Synechocystis sp. PCC 6803 cells grown in the presence of glucose.     

Spectral properties of the CP43-deletion mutant of Synechocystis sp. PCC 6803

Spectral properties, particularly fluorescence spectra and their time-dependent behavior, were investigated for a mutant of the cyanobacterium Synechocystis sp. PCC 6803 lacking the 43 kDa chlorophyll-protein (CP43, PsbC). Lack of CP43 was confirmed by a size shift of the corresponding gene and by Western blotting. The CP43-deletion mutant grown under heterotrophic conditions accumulated a small amount of photosystem (PS) II, but virtually no PS II fluorescence was observed. A 686-nm fluorescence band was clearly observed by phycocyanin excitation, coming from the terminal pigments of phycobilisomes. In contrast, no PS I fluorescence was detected by phycocyanin excitation when accumulation of PS II components was not proved by a fluorescence excitation spectrum, indicating that energy transfer to PS I chlorophyll a was mediated by PS II chlorophyll a. Direct connection of phycobilisomes with PS I was not suggested. Based on these fluorescence properties, the energy flow in the CP43-deletion mutant cells is discussed.     

Phycobilisomes of wild type and pigment mutants of the cyanobacterium Synechocystis PCC 6803

Mutants affected in their pigment content and in the structure of their phycobilosomes (PBS) were isolated in the cyanobacterium Synechocystis PCC 6803 by enriching a population with the inhibitor p-hydroxymercuribenzoate. Three of these mutants, PMB 2, PMB 10 and PMB 11, with original phenotypes, are described. Applying several criteria of analysis (77K absorption and fluorescence, protein electrophoretic patterns, electron microscopy), it was possible to assign the component polypeptides to each substructure of the phycobilisome. The model structure obtained fits with those described in other species PMB 10 and PMB 11, completely lacking PC, are the first source of pure PBS cores available, in which no contamination by residual PC can be feared, and are thus particularly interesting for further biochemical studies. The capacity of genetic transformation of Synechocystis PCC 6803 by chromosomal DNA makes this system very convenient for the analysis of the regulation of synthesis of the PBS constituents.Abbreviations PSI, PSII photosystems I, II - PBS phycobilisomes - PC phycocyanin - APC allophycocyanin - APC-B alophycocyanin B - PE phycoerythrin - PEC phycoerythrocyanin - WT wind type - Chl chlorophyll Present address: Service de Physiologie Microbienne Institut Pasteur, 28, rue du Docteur Roux, F-75724 Paris Cedex 15, France     

State 1-state 2 adaptation in the cyanobacteria Synechocystis PCC 6714 wild type and Synechocystis PCC 6803 wild type and phycocyanin-less mutant

The mechanism of excitation energy distribution between the two photosystems (state transitions) is studied in Synechocystis 6714 wild type and in wild type and a mutant lacking phycocyanin of Synechocystis 6803. (i) Measurements of fluorescence transients and spectra demonstrate that state transitions in these cyanobacteria are controlled by changes in the efficiency of energy transfer from PS II to PS I (spillover) rather than by changes in association of the phycobilisomes to PS II (mobile antenna model). (ii) Ultrastructural study (freeze-fracture) shows that in the mutant the alignment of the PS II associated EF particles is prevalent in state 1 while the conversion to state 2 results in randomization of the EF particle distribution, as already observed in the wild type (Olive et al. 1986). In the mutant, the distance between the EF particle rows is smaller than in the wild type, probably because of the reduced size of the phycobilisomes. Since a parallel increase of spillover is not observed we suggest that the probability of excitation transfer between PS II units and between PS II and PS I depends on the mutual orientation of the photosystems rather than on their distance. (iii) Measurements of the redox state of the plastoquinone pool in state 1 obtained by PS I illumination and in state 2 obtained by various treatments (darkness, anaerobiosis and starvation) show that the plastoquinone pool is oxidized in state 1 and reduced in state 2 except in starved cells where it is still oxidized. In the latter case, no important decrease of ATP was observed. Thus, we propose that in Synechocystis the primary control of the state transitions is the redox state of a component of the cytochrome b ₆/f complex rather than that of the plastoquinone pool.Abbreviations DCCD dicyclohexylcarbodiimide - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DBMIB 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone - EF exoplasmic face - PQ plasto-quinone - PS photosystem - PBS phycobilisome     

A proportion of photosystem II core complexes are decoupled from the phycobilisome in light-state 2 in the cyanobacterium Synechococcus 6301

Cells of Synechococcus 6301 were briefly exposed to a phycocyanin-absorbed light in the presence of DCMU. PS II trap closure was then estimated from fluorescence induction measurements with excitation light absorbed predominantly either by chlorophyll or by phycocyanin. In cells adapted to light-state 2, the exposure to light absorbed by phycocyanin closed only a proportion of the PS II centres that could be closed by exposure to light absorbed by chlorophyll. This distinction was reduced in cells adapted to light-state 1. We conclude that a proportion of PS II core complexes become decoupled from the phycobilisomes during the transition to light-state 2.     

Pigment orientation changes accompanying the light state transition in Synechococcus sp. PCC 6301

Low temperature (77 K) linear dichroism spectroscopy was used to characterize pigment orientation changes accompanying the light state transition in the cyanobacterium, Synechococcus sp. PCC 6301 and those accompanying chromatic acclimation in Porphyridium cruentum in samples stabilized by glutaraldehyde fixation. In light state 2 compared to light state 1 intact cells of Synechococcus showed an increased alignment of allophycocyanin parallel to the cells' long axis whereas the phycobilisomethylakoid membrane fragments exhibited an increased allophycocyanin alignment parallel to the membrane plane. The phycobilisome-thylakoid membrane fragments showed less alignment of a short wave-length chlorophyll a (Chl a) Q_y transition dipole parallel to the membrane plane in state 2 relative to state 1.To aid identification of the observed Chl a orientation changes in Synechococcus, linear dichroism spectra were obtained from phycobilisome-thylakoid membrane fragments isolated from red light-grown (increased number of PS II centres) and green light-grown (increased number of PS I centres) cells of the red alga Porphyridium cruentum. An increased contribution of short wavelength Chl a Q_y transition dipoles parallel to the long axis of the membrane plane was directly correlated with increased levels of PS II centres in red light-grown P. cruentum.Our results indicate that the transition to state 2 in cyanobacteria is accompanied by an increase in the orientation of allophycocyanin and a decrease in the orientation of Chl a associated with PS II with respect to the thylakoid membrane plane.Abbreviations APC - allophycocyanin - Chl a - chlorophyll a - DCMU - 3-(3,4-dichlorophenyl)-1,1-dimethylurea - LD - linear dichroism - LD/A - linear dichroism divided by absorbance - LHC - light-harvesting complex - PBS - phycobilisome - PC - phycocyanin - PS - Photosystem     

Characterization of a Synechococcus sp. strain PCC 7002 mutant lacking Photosystem I. Protein assembly and energy distribution in the absence of the Photosystem I reaction center core complex

A Synechococcus sp. strain PCC 7002 psaAB::cat mutant has been constructed by deletional interposon mutagenesis of the psaA and psaB genes through selection and segregation under low-light conditions. This strain can grow photoheterotrophically with glycerol as carbon source with a doubling time of 25 h at low light intensity (10 E m^–2 s^–1). No Photosystem I (PS I)-associated chlorophyll fluorescence emission peak was detected in the psaAB::cat mutant. The chlorophyll content of the psaAB::cat mutant was approximately 20% that of the wild-type strain on a per cell basis. In the absence of the PsaA and PsaB proteins, several other PS I proteins do not accumulate to normal levels. Assembly of the peripheral PS I proteins PsaC,PsaD, PsaE, and PsaL is dependent on the presence of the PsaA and PsaB heterodimer core. The precursor form of PsaF may be inserted into the thylakoid membrane but is not processed to its mature form in the absence of PsaA and PsaB. The absence of PS I reaction centers has no apparent effect on Photosystem II (PS II) assembly and activity. Although the mutant exhibited somewhat greater fluorescence emission from phycocyanin, most of the light energy absorbed by phycobilisomes was efficiently transferred to the PS II reaction centers in the absence of the PS I. No light state transition could be detected in the psaAB::cat strain; in the absence of PS I, cells remain in state 1. Development of this relatively light-tolerant strain lacking PS I provides an important new tool for the genetic manipulation of PS I and further demonstrates the utility of Synechococcus sp. PCC 7002 for structural and functional analyses of the PS I reaction center.Abbreviations ATCC American type culture collection - Chl chlorophyll - DCMU 3-(3,4-dichlorophyl)-1,1-dimethylurea - DBMIB 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone - HEPES N-[2-hydroxyethyl]piperazine-N-[2-ethanesulfonic acid] - PCC Pasteur culture collection - PS I Photosystem I - PS II Photosystem II - SDS sodium dodecyl sulfate     

State transitions,photosystem stoichiometry adjustment and non-photochemical quenching in cyanobacterial cells acclimated to light absorbed by photosystem I or photosystem II

Cells of the cyanobacterium Synechococcus 6301 were grown in yellow light absorbed primarily by the phycobilisome (PBS) light-harvesting antenna of photosystem II (PS II), and in red light absorbed primarily by chlorophyll and, therefore, by photosystem I (PS I). Chromatic acclimation of the cells produced a higher phycocyanin/chlorophyll ratio and higher PBS-PS II/PS I ratio in cells grown under PS I-light. State 1-state 2 transitions were demonstrated as changes in the yield of chlorophyll fluorescence in both cell types. The amplitude of state transitions was substantially lower in the PS II-light grown cells, suggesting a specific attenuation of fluorescence yield by a superimposed non-photochemical quenching of excitation. 77 K fluorescence emission spectra of each cell type in state 1 and in state 2 suggested that state transitions regulate excitation energy transfer from the phycobilisome antenna to the reaction centre of PS II and are distinct from photosystem stoichiometry adjustments. The kinetics of photosystem stoichiometry adjustment and the kinetics of the appearance of the non-photochemical quenching process were measured upon switching PS I-light grown cells to PS II-light, and vice versa. Photosystem stoichiometry adjustment was complete within about 48 h, while the non-photochemical quenching occurred within about 25 h. It is proposed that there are at least three distinct phenomena exerting specific effects on the rate of light absorption and light utilization by the two photoreactions: state transitions; photosystem stoichiometry adjustment; and non-photochemical excitation quenching. The relationship between these three distinct processes is discussed.Abbreviations Chl chlorophyll - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - F relative fluorescence intensity at emission wavelength nm - F _o fluorescence intensity when all PS II traps are open - light 1 light absorbed preferentially by PS I - light 2 light absorbed preferentially by PS II - PBS phycobilisome - PS photosystem     

Cobalt induced changes in photosystem activity in Synechocystis PCC 6803: Alterations in energy distribution and stoichiometry

Adaptive responses to excess (supraoptimal) level of cobalt supplied to the growth medium were studied in the cyanobacterium Synechocystis PCC 6803. Growth of cells in the medium containing 10 M CoCl₂ led to a large stimulation (50%) in O₂-evolution and an overall increase (30%) in the photosynthetic electron transport rates. Analysis of variable Chl a fluorescence yield of PS II and immuno-detection of Photosystem II (PS II) reaction-center protein D1, showed a small increase (15–20%) in the number of PS II units in cobalt-grown cells. Cobalt-grown cells, therefore, had a slightly elevated PS II/PS I ratio compared to control.We observed alteration in the extent of energy distribution between the two photosystems in the eobalt grown cells. Energy was preferentially distributed in favour of PS II accompanied by a reduction in the extent of energy transfer from PS II to PS I in cobalt-grown cells. These cells also showed a smaller PS I absorption cross-section and a smaller size of intersystem electron pool than the control cells. Thus, our results suggest that supplementation of 10 M CoCl₂, to the normal growth medium causes multiple changes involving small increase in PS II to PS I ratio, enhanced funneling of energy to PS II and an increase in PS I electron transport, decrease PS I cross section and reduction in intersystem pool size. The cumulative effects of these alterations cause stimulation in electron transport and O₂ evolution.Abbreviations BCIP 5-bromo-4-chloro-3-indolylphosphate - Chl a Chlorophyll a - Cyt blf Cytochrome blf - DCBQ 2,6-dichlorobenzoquinone - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethyl urea - DCPIP 2,6-dichlorophenol indophenol - DPC Diphenyl carbazide - F_o fluorescence when all reaction centers are open - F_M fluorescence yield when all reaction centers are closed - F_v variable chlorophyll fluorescence - HEPES N-2-hydroxyethyl piperazine-N'-2-ethanesulphonic acid - MV methyl viologen - NBT nitro-blue tetrazolium - pBQ para-benzoquinone - PB somes phycobilisomes - PC Phycocyanin - PQ plastoquinone - PS I Photosystem I - PS II Photosystem II - P700 reaction center Chl a of PS 1 - ST-and MT-flash single turnover and multiple turnover flash     

Changes in composition of membrane proteins accompanying the regulation of PS I/PS II stoichiometry observed with Synechocystis PCC 6803

Changes in composition of membrane proteins in Synechocystis PCC 6803 induced by the shift of light regime for photosynthetic growth were studied in relation to the regulation of PS I/PS II stoichiometry. Special attention was paid to the changes in abundance of proteins of PS I and PS II complexes. Composition was examined using a LDS-PAGE and a quantitative enzyme immunoassay. Abundance of PsaA/B polypeptides and the PsaC polypeptide of the PS I complex, on a per cell basis, increased under the light regime exciting preferentially PS II and decreased under the light regime exciting mainly PS I. Similar changes were observed with polypeptides of 18.5, 10 and 8.5 kDa. The abundance of other proteins associated with membranes, including PsbA polypeptide of the PS II complex, was fairly constant irrespective of light regime. These results are consistent with our previous observations with other strains of cyanophytes (Anabaena variabilis M2 and Synechocystis PCC 6714) that PS I is the variable component in changes in PS I/PS II stoichiometry in response to changing light regimes for photosynthesis.Abbreviations CBB Coomassie brilliant blue - Chl chlorophyll - EIA enzyme immunoassay - LDS lithium dodecyl sulfate - PAGE polyacrylamide gel electrophoresis - PS photosystem - PVDF polyvinylidene difluoride     

Resolution of low-energy chlorophylls in Photosystem I of Synechocystis sp. PCC 6803 at 77 and 295 K through fluorescence excitation anisotropy

Fluorescence excitation spectra of highly anisotropic emission from Photosystem I (PS I) were measured at 295 and 77 K on a PS II-less mutant of the cyanobacterium Synechocystis sp. PCC 6803 (S. 6803). When PS I was excited with light at wavelengths greater than 715 nm, fluorescence observed at 745 nm was highly polarized with anisotropies of 0.32 and 0.20 at 77 and 295 K, respectively. Upon excitation at shorter wavelengths, the 745-nm fluorescence had low anisotropy. The highly anisotropic emission observed at both 77 and 295 K is interpreted as evidence for low-energy chlorophylls (Chls) in cyanobacteria at room temperature. This indicates that low-energy Chls, defined as Chls with first excited singlet-state energy levels below or near that of the reaction center, P700, are not artifacts of low-temperature measurements.If the low-energy Chls are a distinct subset of Chls and a simple two-pool model describes the excitation transfer network adequately, one can take advantage of the low-energy Chls' high anisotropy to approximate their fluorescence excitation spectra. Maxima at 703 and 708 nm were calculated from 295 and 77 K data, respectively. Upper limits for the number of low-energy Chls per P700 in PS I from S. 6803 were calculated to be 8 (295 K) and 11 (77 K).Abbreviations Chl - chlorophyll - BChl - bacteriochlorophyll - LHC - light-harvesting chlorophyll - PS - Photosystem - RC - reaction center - S. 6803 - Synechocystis sp. PCC 6803     

Temperature dependence and polarization of fluorescence from Photosystem I in the cyanobacterium Synechocystis sp. PCC 6803

To determine the fluorescence properties of cyanobacterial Photosystem I (PS I) in relatively intact systems, fluorescence emission from 20 to 295 K and polarization at 77 K have been measured from phycobilisomes-less thylakoids of Synechocystis sp. PCC 6803 and a mutant strain lacking Photosystem II (PS II). At 295 K, the fluorescence maxima are 686 nm in the wild type from PS I and PS II and at 688 nm from PS I in the mutant. This emission is characteristic of bulk antenna chlorophylls (Chls). The 690-nm fluorescence component of PS I is temperature independent. For wild-type and mutant, 725-nm fluorescence increases by a factor of at least 40 from 295 to 20 K. We model this temperature dependence assuming a small number of Chls within PS I, emitting at 725 nm, with an energy level below that of the reaction center, P700. Their excitation transfer rate to P700 decreases with decreasing temperature increasing the yield of 725-nm fluorescence.Fluorescence excitation spectra of polarized emission from low-energy Chls were measured at 77 and 295 K on the mutant lacking PS II. At excitation wavelengths longer than 715 nm, 760-nm emission is highly polarized indicating either direct excitation of the emitting Chls with no participation in excitation transfer or total alignment of the chromophores. Fluorescence at 760 nm is unpolarized for excitation wavelengths shorter than 690 nm, inferring excitation transfer between Chls before 760-nm fluorescence occurs.Our measurements illustrate that: 1) a single group of low-energy Chls (F725) of the core-like PS I complex in cyanobacteria shows a strongly temperature-dependent fluorescence and, when directly excited, nearly complete fluorescence polarization, 2) these properties are not the result of detergent-induced artifacts as we are examining intact PS I within the thylakoid membrane of S. 6803, and 3) the activation energy for excitation transfer from F725 Chls to P700 is less than that of F735 Chls in green plants; F725 Chls may act as a sink to locate excitations near P700 in PS I.Abbreviations Chl chlorophyll - BChl bacteriochlorophyll - PS Photosystem - S. 6803 Synechocystis sp. PCC 6803 - PGP potassium glycerol phosphate     

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     

Shade adaptation in cyanobacteria

Growth of Anacystis in high light in the presence of sublethal concentrations of DCMU-type inhibitors leads to an increased synthesis of phycocyanin paralleled by a reduced rate of ³⁵S methionine incorporation into the D1 protein compared to the high light controls, as is characteristic for naturally-induced shade phenotype. On the contrary, sun phenotype is characterized by a low rate of antenna synthesis, but a high rate of ³⁵S methionine incorporation into the D1 protein.Room temperature excitation spectra of 684 nm fluorescence emission clearly demonstrate the participation of the extraordinarily high concentration of phycocyanin in artificially shade-adapted cells in excitation energy transfer to chlorophyll.It could be shown that the development of shade-type appearance is not simply the consequence of an imbalance in electron transport, since an addition of thiosulphate to cultures growing in high light in the presence of DCMU-type inhibitors can only partially prevent or revert the change from sun to artificial-herbicide-induced-shade phenotype. This is regarded as evidence that the dynamic herbicide-binding D1 protein itself may play a role as a light meter in the process of natural shade adaptation, the rate of its degradation and resynthesis possibly giving the signal for the adaptive reorganization of the photosynthetic apparatus. The chain of signal transduction remains to be established.Abbreviations atrazine 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine - chl chlorophyll - D1 reaction center polypeptide carrying the secondary plastoquinone electron acceptor of PS II - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - PAGE polyacrylamide gel electrophoresis - PAR photosynthetically active radiation - PC phycocyanin - PCC Pasteur Culture Collection - PS photosystem - Q_B secondary plastoquinone electron acceptor of PS II - SAUG Sammlung von Algenkulturen am Pflanzenphysiologischen Institut der Universtität Göttingen - SDS sodium dodecyl sulphate Dedicated to Professor Wilhelm Menke on the occasion of his 80th birthday.