Damages of photosynthetic apparatus inAnacystis nidulans by ultraviolet-B radiation

Changes in photosystem (PS) 2 activity were measured inAnacystis nidulans cells exposed to UV-B irradiation. The decrease in PS 2 activity was biphasic in cells exposed at the surface (0 cm) and at 2 cm depth in the water column, while gradual in those exposed at 10 and 30 cm depth. Addition of supplemental “white light” reduced the extent of UV-B damage. Decrease in photosynthetic activity was primarily due to the loss of energy transfer from phycobilisome to chlorophyll as the former in cyanobacteria acts as the primary light-harvesting complex. This was supported by the absorption and fluorescence excitation and emission spectral studies. All these changes were proportionally reduced by the thickness of the water column that reduced UV-B irradiance. This work was supported in part by a grant from the Ministerio de Education y Ciencia (ref SB 94-AM086772) to N. N.     

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     

Phosphatase activities in spinach thylakoid membranes-effectors, regulation and location

The dephosphorylation of seven phosphoproteins associated with Photosystem II or its chlorophyll a/b antenna in spinach thylakoids, was characterised. The rates were found to fall into two distinct groups. One, rapidly dephosphorylated, consisted of the two subunits (25 and 27 kD) of the major light harvesting complex of Photosystem II (LHC II) and a 12 kD polypeptide of unknown identity. A marked correlation between the dephosphorylation of these three phosphoproteins, strongly suggested that they were all dephosphorylated by the same enzyme. Within this group, the 25 kD subunit was consistently dephosphorylated most rapidly, probably reflecting its exclusive location in the peripheral pool of LHC II. The other group, only slowly dephosphorylated, included several PS II proteins such as the D1 and D2 reaction centre proteins, the chlorophyll-a binding protein CP43 and the 9 kD PS II-H phosphoprotein. No dephosphorylation was observed in either of the two groups in the absence of Mg²⁺-ions. Dephosphorylation of the two LHC II subunits took place in both grana and stroma-exposed regions of the thylakoid membrane. However, deposphorylation in the latter region was significantly more rapid, indicating a preferential dephosphorylation of the peripheral (or mobile) LHC II. Dephosphorylation of LHC II was found to be markedly affected by the redox state of thiol-groups, which may suggest a possible regulation of LHC II dephosphorylation involving the ferredoxin-thioredoxin system.Abbreviations CP 43 43 kD chlorophyll a- binding protein - D1 and D2 reaction centre proteins of PS II - LHC II light-harvesting complex of PS II - LHC II-25 25 kD subunit of LHC II - LHC II-27 27 kD subunit of LHC II - NEM N-ethylmaleimide - PP2C protein phosphatase 2C - PS II-H psb H gene product     

Polypeptide sequence of the chlorophyll a/b/c-binding protein of the prasinophycean alga Mantoniella squamata

The primary structure of the Chla/b/c-binding protein from Mantoniella squamata is determined. This is the first report that protein sequencing reveals one modified amino acid resulting in a LHCP-specific TFA-cleavage site. The comparison of the sequence of Mantoniella with other Chla/b-and Chla/c-binding proteins shows that the modified amino acid is located in a region which is highly conserved in all these proteins. The alignment also reveals that the LHCP of Mantoniella is related to the Chla/b-binding proteins. Finally, possible Chl-binding regions are discussed.Abbreviations a.m.u. atomic mass unit - LHC light-harvesting complex - LHC II major LHC of Photosystem II - LHCP light-harvesting chlorophyll-binding protein - LSIMS liquid secondary ion mass spectrometry - TFA trifluoroacetic acid     

Survival Strategy of Photosynthetic Organisms. 2. Experimental Proof of the Size Variability of the Unit Building Block of Light-Harvesting Oligomeric Antenna

The present series of papers is part of an integrated research program to understand the effective functional strategy of natural light-harvesting molecular antennae in photosynthetic organisms. This work tackles the problem of the structural optimization of light-harvesting antennae of variable size. In vivo, this size is controlled by light intensity during growth, thus implying more sophisticated optimization strategies, since larger antenna size demands finer structural tuning. Earlier modeling experiments showed that the aggregation of the antenna pigments, apart from being itself a universal structural factor optimizing the performance of light-harvesting antenna with any (!) spatial lattice, maintains its functioning provided that the degree of aggregation varies: the larger the unit building block, the higher the efficiency of the whole structure. It means that altering the degree of pigment aggregation in response to the antenna size is biologically expedient. In the case of the oligomeric chlorosomal antenna of green bacteria, the strategy of optimizing the variable antenna structure in response to the illumination intensity was demonstrated to take place in vivo and ensure high antenna efficiency regardless of its size, thus allowing bacteria to survive in a broad range of light intensities.     

Structural factors which control the position of the Qy absorption band of bacteriochlorophyll a in purple bacterial antenna complexes

This paper presents a concise review of the structural factors which control the energy of the Q_y absorption band of bacteriochlorophyll a in purple bacterial antenna complexes. The energy of these Q_y absorption bands is important for excitation energy transfer within the bacterial photosynthetic unit. This revised version was published online in June 2006 with corrections to the Cover Date.     

Photoprotection in higher plants: The putative quenching site is conserved in all outer light-harvesting complexes of Photosystem II

In bright sunlight, the amount of energy harvested by plants exceeds the electron transport capacity of Photosystem II in the chloroplasts. The excess energy can lead to severe damage of the photosynthetic apparatus and to avoid this, part of the energy is thermally dissipated via a mechanism called non-photochemical quenching (NPQ). It has been found that LHCII, the major antenna complex of Photosystem II, is involved in this mechanism and it was proposed that its quenching site is formed by the cluster of strongly interacting pigments: chlorophylls 611 and 612 and lutein 620 [A.V. Ruban, R. Berera, C. Ilioaia, I.H.M. van Stokkum, J.T.M. Kennis, A.A. Pascal, H. van Amerongen, B. Robert, P. Horton and R. van Grondelle, Identification of a mechanism of photoprotective energy dissipation in higher plants, Nature 450 (2007) 575-578.]. In the present work we have investigated the interactions between the pigments in this cluster not only for LHCII, but also for the homologous minor antenna complexes CP24, CP26 and CP29. Use was made of wild-type and mutated reconstituted complexes that were analyzed with (low-temperature) absorption and circular-dichroism spectroscopy as well as by biochemical methods. The pigments show strong interactions that lead to highly specific spectroscopic properties that appear to be identical for LHCII, CP26 and CP29. The interactions are similar but not identical for CP24. It is concluded that if the 611/612/620 domain is responsible for the quenching in LHCII, then all these antenna complexes are prepared to act as a quencher. This can explain the finding that none of the Lhcb complexes seems to be strictly required for NPQ while, in the absence of all of them, NPQ is abolished.     

UNIQUE LOCATION OF THE PHYCOBILIPROTEIN LIGHT-HARVESTING PIGMENT IN THE CRYPTOPHYCEAE1

The cryptophyte algae, or cryptomonads, comprise a small algal group with a unique photosynthetic apparatus. Both a chlorophyll a/c₂ light-harvesting complex and a phycobiliprotein antenna (which can be either phycoerythrin or phycocyanin) are present, with the phycobiliprotein playing the major role in harvesting light for photosynthesis. Longstanding circumstantial evidence suggested that, in cryptophytes, the phycobiliprotein is located in the intrathylakoid space (thylakoid lumen) rather than on the outer surface of the thylakoid as part of a phycobilisome as in other algae. We used immunogold labeling to show conclusively that 1) the phycoerythrin (PE) of the cryptophyte Rhodomonas lens Pascher and Ruttner is located within the intrathylakoid space, 2) the PE is not exclusively bound to the thylakoid membrane but instead is distributed across the thylakoid lumen and 3) a fraction of this PE is tightly associated with the thylakoid membrane. The thylakoids are not everted to compensate for this unusual arrangement. The location of the major light-harvesting pigment on the “wrong” side of the otherwise very normal photo-synthetic membrane is unexpected, unique to the cryptophytes, and, remarkably, does not impair the photosynthetic abilities of this organism. A model is presented which incorporates these results -with previous information to give a complete structural picture of the cryptophyte light-harvesting apparatus.     

High-irradiance Stress and Photochemical Activities of Photosystems 1 and 2 in vivo

High-irradiance (HI) stress induced changes in the photosynthetic energy storage (ES) of photosystems 1 (ESPS1) and 2 (ESPS2) were studied with 650 nm modulated radiation in intact sugar maple (Acer saccharum Marsh.) leaves. HI-treatment (420 W m-2, 1 h) caused an inhibition of about 40 % in ESPS2 and an enhancement of about 60 % in ESPS1. The rate of PS1 cyclic electron transport, measured with 705 nm modulated radiation, also increased in HI-treated leaves. There was a clear state 1- state 2 transition in HI-treated leaves. ESPS1 increased significantly and ESPS2 decreased drastically in leaves preadapted to state 1 after HI (600 W m-2, 30 min) treatment. Thus, the increase in PS1 activity observed immediately after HI-treatment in leaves preadapted to state 1 can be due to the coupling of LHC2 to PS1 during the HI-treatment. Further, the dissociation of LHC2 from PS2 during the HI-treatment resulted in apparently (about 15 %) greater inhibition than the "true" inhibition of PS2 activity. The presence of LHC2 with PS2 (state 1) at the time of HI-treatment caused no additional damage to PS2 or its coupling to PS1 offered no apparent HI-treatment. Further, the dissociation of LHC2 from PS2 during the HI-treatment resulted in apparently (about 15 %) greater inhibition than the "true" inhibition of PS2 activity. The presence of LHC2 with PS2 (state 1) at the time of HI-treatment caused no additional damage to PS2 or its coupling to PS1 offered no apparent protection to the photosynthetic apparatus.     

Species-related differences in the electrophoretic behavior of CP 29 and CP 26: An immunochemical analysis

The monomeric chlorophyll-protein complexes, CP 29 and CP 26 seen in the Camm and Green (1980) and Dunahay and Staehelin (1986) green gels do not always migrate in the order of the apparent molecular weight of their apoproteins as determined by denaturing gel electrophoresis. In barley and corn they do, but in spinach they do not. In addition, in some higher plant species these chlorophyll-protein complexes comigrate on green gels causing confusion in the literature. To remedy this situation and circumvent future confusion, we propose that the CP 29 and CP 26 complexes be named according to the relative molecular weight of their apoproteins on denaturing gels. Our proposal is supported by the results obtained from four antibodies used on Western blot samples of whole thylakoids, grana membranes, and PS II preparations from different plants. The higher molecular weight proteins (proposed CP 29's) react strongly to one set of antibodies, and the lower molecular weight proteins (proposed CP 26's) react strongly to a different set. In spinach, CP 26 antibodies react also with CP 29, but the extent of the cross-reactivity depends critically on the gel electrophoresis system used. Accordingly, a lack of antibody reactivity under certain conditions may not indicate two proteins are unrelated, just simply that a particular epitope is no longer accessible following gel electrophoresis with a particular buffer system.Abbreviations CP Chlorophyll-protein - ammediol 1,2, amino-methyl-propanediol - Tris tris(hydroxymethyl)aminomethane - TBS Tris-buffered saline - MES 2-[N-Morpholino]ethane sulfonic acid - PS II Photosystem II - LHC II light harvesting polypeptides of PS II - BBY stacked membrane preparation of Berthold, Babcock and Yocum - HRP horseradish peroxidase - AP alkaline phosphatase - PVDF polyvinylidene fluoride - BSA bovine serum albumin - KLH keyhole limpet hemocyanin     

PHOTOSYNTHETIC PIGMENT ORGANIZATION IN DIATOMS (BACILLARIOPHYCEAE)1

The isolation and characterization of six pigment-protein complexes from five diatom species (Phaeodactylum tricornutum Bohlin, Chaetoceros gracilis Schutt, Nitzschia sp. Mono Lake, Nitzschia laevis Hust. and Thalassiosira pseudonana (Hust.) Hasle and Heimdal) was accomplished by membrane dissociation with digitonin followed by gel electrophoresis. Six analogous complexes obtained from all species were correlated in spectral characteristics and relative mass with complexes from higher plants obtained by the same procedure. The largest of these complexes, comprising about 15% of the total Chl a, contained reaction centers of Photosystem I (PSI) and antenna pigments (LHC₁).Some PSI complexes also separated from LHC₁ in the gel. For the first time in diatoms, a Photosystem II complex was isolated and identified from its position in the gels, absorption and fluorescence spectra, lack of P700, and enrichment carotene. Three antenna pigment-protein complexes in addition to LHC₁ occurred in varying proportion under different experimental conditions but in sum, they accounted for 70% of the total Chl a. All three bands were highly enriched in Chl c and fucoxanthin, although the ratio of Chl c/ xanthophyll decreased between the slowest migrating LHC₂ and fastest moving LHC₄ LHC₃ contained the highest proportio of pigment-protein and was composed primarily of polypeptides of about 18,000 D. Essentially all α- and β-carotene was bound to the reaction center complexes. The Nitzschia from Mono Lake differed from the other species in that PSI complexes could not be readily dissociated from its membrane by digitonin treatment, a characteristic which may reflect a different chloroplast membrane structure in this alga.     

Studies on the light-harvesting complexes from the thermotolerant purple bacterium Rhodopseudomonas cryptolactis

The antenna complexes from Rps. cryptolactis have been isolated and purified. Rps. cryptolactis contains two types of variable antenna complex, B800-850 and B800-820 as well as the core B875 antenna complex. The variable antenna complexes contain more than two types of antenna apoprotein, and have a Bchla:carotenoid ratio of 2:1. They can both be crystallised, but the B800-820 complex is the easiest with which to get relatively large single 3-D crystals (up to 0.5 mm in each dimension).     

PRESENCE OF PHYCOERYTHRIN IN TWO STRAINS OF PROCHLOROCOCCUS (CYANOBACTERIA) ISOLATED FROM THE SUBTROPICAL NORTH PACIFIC OCEAN

Prochlorococcus is a ubiquitous marine oxyphotobacterium characterized by the presence of DV-chl a and b . In addition, the type strain Prochlorococcus marinus Chisholm et al. CCMP 1375 (or SS120), an isolate from the Sargasso Sea, contains low levels of an unusual phycoerythrin. Until now, it has been unclear if phycoerythrin occurs randomly within this systematic group and if the molecular characteristics of this phycoerythrin are restricted to this single strain. Here, we show that two additional Prochlorococcus strains from the Pacific Ocean also contain similar low levels of phycoerythrin. DNA sequence and phylogenetic analyses demonstrated that this phycoerythrin is very similar to the phycoerythrin of P. marinus SS120 and differs from the classic cyanobacterial phycoerythrins. In contrast, a third isolate from the Arabian Sea lacks phycoerythrin. Based on the DV-chl b:a ratio and 16S rRNA sequence data, we classify the two Pacific phycoerythrin-containing isolates as low-light-adapted strains and the Arabian Sea isolate as a high-light-adapted strain. Thus, we provide further evidence to link the physiology of an individual genotype and the presence or absence of functional phycoerythrin genes within the genus Prochlorococcus .     

Acquirement and characterization of a carotenoid mutant (GM309) of <Emphasis Type="Italic">Rhodobacter sphaeroides</Emphasis> 601

A green mutant was obtained among the chemically induced mutants of Rhodobacter sphaeroides 601 (RS601) and named GM309. A blue shift of 20 nm of the carotenoid absorption spectrum was found in the light-harvesting complex II (LH2) of GM309. Different from LH2 of RS601, it was found that the carotenoids in GM309-LH2 changed to be neurosporene by mutation. Neurosporene lacks a conjugate double bond, compared with the spheroidene in RS601-LH2 which has ten conjugate double bonds. As shown by absorption and circular dichroism spectroscopy, the overall structure of GM309-LH2 is little affected by this change. From fluorescence emission spectra, it is found that GM309-LH2 can transfer energy from carotenoids to Bchl-B850 without any change in efficiency. But the efficiency of energy transfer from B800 to B850 in GM309-LH2 is decreased to be 42% of that of the native. This work would provide a novel method to investigate the mechanism of excitation energy transfer in LH2.     

The resolution and biochemical characterization of subcomplexes of the main light-harvesting chlorophyll a/b-protein complex of Photosystem II (LHC II)

LHC II isolated from carnation leaves has been solubilized and resolved by a newly developed, vertical-bed non-denaturing isoelectric focusing in polyacrylamide slab gels to yield three trimeric subcomplexes focusing at pH 4.52, 4.42 and 4.37 (designated a, b and c, respectively), comprising approximately 38%, 24% and 38% of the chlorophyll. The spectroscopic data demonstrated a close similarity among LHC II subcomplexes concerning their chlorophyll content and organization. The most alkaline and the most acidic subcomplex contained the 27 kDa polypeptide of LHC II while the intermediate pI fraction contained both LHC II polypeptides, i.e. 27 kDa and 26 kDa ones associated at 2:1 stoichiometry. The 27 kDa polypeptide could be resolved by denaturing isoelectrofocusing into 10 pI molecular isoforms covering 5.90–4.20 pH range. Three of the isoforms were found in the subcomplexes a and b and eight in the subcomplex c. The 26 kDa polypeptide comprised the unique pI molecular isoform focusing at pH 5.61.Abbreviations CBB G-250 Coomassie Brilliant Blue G-250 - chl chlorophyll - DM n-dodecyl--d-maltoside - EDTA ethylendiaminotetraacetic acid - IEF isoelectric focusing - LHC II the main light-harvesting chlorophyll a/b-protein complex of Photosystem II - LHCP II apoprotein of the main light-harvesting chlorophyll a/b-protein complex of Photosystem II - NP-40 polyethyleneglycol-p-isooctylphenyl ether - pI isoelectric point - OG octyl--d-glucopyranoside - PS II Photosystem II - SDS-PAGE sodium dodecylsulphate polyacrylamide gel electrophoresis - TCA trichlorooacetic acid     

Spectroscopy of non-photochemical and photochemical quenching of chlorophyll fluorescence in leaves; evidence for a role of the light harvesting complex of Photosystem II in the regulation of energy dissipation

Dissipation of absorbed excitation energy as heat, measured by its effect on the quenching of chlorophyll fluorescence, is induced under conditions of excess light in order to protect the photosynthetic apparatus of plants from light-dependent damage. The spectral characteristics of this quenching have been compared to that due to photochemistry in the Photosystem II reaction centre using leaves of Guzmania monostachia. This was achieved by making measurements at 77K when fluorescence emission bands from each type of chlorophyll protein complex can be distinguished. It was demonstrated that photochemistry and non-photochemical dissipation preferentially quench different emission bands and therefore occur by dissimilar mechanisms at separate sites. It was found that photochemistry was associated with a preferential quenching of emission at 688 nm whereas the spectrum for rapidly reversible non-photochemical quenching had maxima at 683 nm and 698 nm, suggesting selective quenching of the bands originating from the light harvesting complexes of Photosystem II. Further evidence that this was occurring in the light harvesting system was obtained from the fluorescence excitation spectra recorded in the quenched and relaxed states.Abbreviations pH transthylakoid pH gradient - F_o minimum level of chlorophyll fluorescence when Photosystem II reaction centres are open - F_m maximum level of fluorescence when Photosystem II reaction centres are closed - F_v variable fluorescence F_m minus F_o - F'_o F_o in any quenched state - F_m F_m in any quenched state - LHCII light harvesting complexes of Photosystem II - PSI Photosystem I - PS II Photosystem II - qN non-photochemical quenching of chlorophyll fluorescence - qE non-photochemical quenching of chlorophyll fluorescence that occurs in the presence of a pH     

Biochemical and Immunochemical Investigations on the Light-Harvesting System of the Cryptophyte Rhodomonas sp.: Evidence for a Photosystem I Specific Antenna

Abstract: Thylakoid membranes of the cryptophyte Rhodomonas sp. were solubilized with the mild detergent dodecyl-β-maltoside and subjected to sucrose density gradient centrifugation. The resulting gradients showed six pigment-bearing bands which were characterized further by means of absorption and fluorescence emission (77K) spectroscopy, polyacrylamide gel electrophoresis and Western immunoblotting. Two of the bands showed characteristics of light-harvesting complexes, other bands could be attributed to photosystem II and photosystem I. Up to 10 different light-harvesting proteins could be identified, some of which are specific for photosystem I, others for photosystem II. The polypeptides of the light-harvesting complex of photosystem II show a higher chlorophyll c/a ratio than the antenna proteins of photosystem I. As in vascular plants, they represent the bulk of the membrane-intrinsic light-harvesting proteins.     

管藻目绿藻刺松藻PSⅡ捕光复合物多肽结构分析

对管藻目绿藻刺松藻 (Codiumfragile (Sur.)Hariot.)的 4种主要的捕光复合物LHCP1-3 和LHCP3′的多肽组成和相互关系进行了研究。LHCP1在SDS_PAGE中主要呈现 34 .4、31.5、2 9.5、2 8.2和 2 6 .5kD 5种多肽 ,其中 34 .4和31.5kD多肽是高等植物所没有的 ;LHCP3 含有LHCP1中除了 34 .4kD多肽以外的其他 4种多肽 ,而LHCP3′只含有2 8.2和 2 6 .5kD两种多肽。若LHCP1不经处理直接进行SDS_PAGE ,发现较易从LHCP1上脱落的是 34 .4、2 8.2和2 6 .5kD多肽 ,这表明它们可能位于较外侧 ,而 31.5和 2 9.5kD多肽则靠近核心 ;2 8和 2 6kD两种多肽常出现在刺松藻的中心复合物CPa中 ,可能是与CCⅡ结合最为紧密的LHCⅡ多肽。根据上述结果提出了 1个LHCP1多肽结构关系示意图