Seasonal Effects on Chlorophyll-Protein Complexes Isolated from P-inus silvestris

The seasonal changes in the relative distribution of P700 chlorophyll-protein complex a₁ and light harvesting chlorophyll-protein complex a/b were studied in a natural stand of Pinus silvestris. Similar measurements were made after artificial photobleaching of chlorophyll in pine seedlings or in isolated pine chloroplasts. The chlorophyll-protein complexes were solubilized by sodium dodecyl sulphate and separated by polyacrylamide gel electrophoresis. When autumn and winter destruction of chlorophyll occurs, the chlorophyll a antenna associated with P700 in photosystem 1 (P700-CPa₁) is relatively more affected than the light harvesting complex, which lacks a reaction centre. These results are further supported by low-temperature fluorescence emission properties of isolated chloroplasts presented in this work and elsewhere. The destruction of chlorophyll in stressing autumn and winter climates is most probably caused by photosensitized oxidation of chlorophyll.     

P(700) Chlorophyll a-Protein : Purification, Characterization, and Antibody Preparation

The P₇₀₀ chlorophyll α-protein was purified by preparative sodium dodecyl sulfate (SDS) gel electrophoresis from SDS-solubilized barley (Hordeum vulgare L., cv Himalaya) chloroplast membranes. After elution from the gel in the presence of 0.05 to 0.1% Triton X-100, the recovered protein had a chlorophyll/P₇₀₀ ratio of 50 to 60/1 and contained no chlorophyll b or cytochromes. Analysis of the polypeptide composition of the chlorophyll-protein revealed a 58 to 62 kilodalton (kD) polypeptide component but no lower molecular weight polypeptides. The 58 to 62 kD component was further resolved into two distinct polypeptide bands which were subsequently mapped by partial cyanogen bromide digestion and Staphylococcus aureus proteolysis. Based on results from the mapping experiments and other data, we suggest that the two components are conformational variants of a single polypeptide. Measurement of the chlorophyll to protein ratio by quantitative amino acid analysis and consideration of the yield of P₇₀₀ in the protein isolate suggest that, contrary to previous models (Bengis and Nelson, 1975, 1977), P₇₀₀in vivo is associated with a minimum of four subunits of approximately 60 kD.

Antibodies raised against the photochemically active chlorophyll-protein complex from barley reacted specifically with the 58 to 62 kD apoprotein. The same preparative electrophoresis procedure was used to isolate photochemically active P₇₀₀ chlorophyll a-protein from soybean (Glycine max L.), tobacco (Nicotiana tobacum L.), petunia (Petunia × hybrida), tomato (Lycopersicum esculentum), and Chlamydomonas reinhardti. The isolated complex from all species exhibited identical polypeptide compositions and chlorophyll/P₇₀₀ ratios. Antibodies to the barley protein cross reacted with all species tested demonstrating the highly conserved structure of the apoprotein.

     

Structural and functional relationships in developing Pinus silvestris chloroplasts

The light dependent chloroplast development of dark grown seedlings of Pinus silvestris L. was followed by analyses of chlorophyll content, chlorophyll a/b ratios, chlorophyll/P700 ratios, chlorophyll-protein complexes and structural changes. Low-temperature fluorescence emission spectra of isolated chloroplasts and separation of sodium dodecyl sulphate solubilized chlorophyll-protein complexes by gel electrophoresis showed that the chlorophyll-protein complexes of photosystem 1 (P700-CPa), photosystem II (PS II-CPa) and the light-harvesting complex LH–CPa/b were present in dark grown seedlings. The low-temperature fuoorescence emission maxima of isolated P700–CPa and PS II–CPa shifted towards longer wavelengths during greening in light, indicating a light induced change of the chlorophyll organisation in the two photosystems. Illumination caused LH–CPa/b to increase relative to P700–CPa, whereas the ratio between LH–CPa/b and PS II–CPa remained essentially constant. Analyses of low-temperature fluorescence spectra with or without 0.01 M Mg²⁺ showed that the Mg²⁺ controlled distribution of excitation energy into PS I was activated upon illumination of the seedlings. The photosynthetic unit size, as defined by the chlorophyll/P700 ratio, did not change over a 96 h illumination period, although the chlorophyll content increased about 6–fold during that time. This result and the constant electron transport rate per unit chlorophyll and time during chlorophyll accumulation provided evidence for a sequential development of the photosynthetic units when illuminating dark grown pine cotyledons. Electron micrographs showed that exposure of dark grown seedlings to light for 2 h caused the prolamellar body to disappear and grana to form. These changes occurred prior to substantial accumulation of chlorophyll or change in the ratio between LH–CPa/b and P700–CPa. However, both the water-splitting system of photosystem II and the Mg²⁺ controlled redistribution of excitation energy was activated during this period.     

Structural studies on cyanobacterial photosystem I

The cyanobacterial photosystem, I complex from Synechococcus sp. PCC6301 contains polypeptides of apparent M_r of 70,000, 18,000, 17,700, 16,000 and 10,000. Procedures were developed for the purification of the M_r 17,700 and 10,000 polypeptides. Amino acid analyses showed the absence of cystine and cysteine from these polypeptides. Amino-terminal sequences of 98 residues for the M_r 17,700 polypeptide and of 42 residues for the M_r 10,000 polypeptide were determined. Studies of pigment distribution within the photosystem I complex indicated that the binding of chlorophyll a and -carotene is in part dependent on the presence of these polypeptides.Abbreviations PSI photosystem I - P700 reaction center of PSI - SDS sodium dodecylsulfate - TBS tris-buffered saline - TTBS TBS containing Tween-20     

Sequential extraction of chlorophyll from chlorophyll-protein complexes in lyophilized pea thylakoids with solvents of different polarity

Lyophilized chloroplasts of Pisum sativum (pea) have been extracted with petroleum ether of different polarity (obtained by adding varying amounts of ethanol to the petroleum ether). Extracted thylakoids have then been solubilized by sodium dodecyl sulphate (SDS) and chlorophyll-protein complexes have been isolated by polyacrylamide gel electrophoresis (PAGE). Absorption- and low temperature fluorescence emission spectro-scopy have been used to characterize thylakoids and purified chlorophyll-protein complexes. Weakly polar solvents extracted mainly chlorophyll a. SDS-PAGE scan profiles of similarly extracted thylakoids contained no photosystem II chlorophyll a reaction center antennae (CP-a_n) and the amount of photosystem I chlorophyll a reaction center antennae (CP-a₁) was reduced as compared with an unextracted control. This was due partly to the extraction of chlorophyll a prior to SDS-PAGE, and partly to the increased solubilization of chlorophyll a by SDS as a result of β-carotene extraction. By increasing the polarity of the solvent CP-a₁ also disappeared in the scan profile, leaving only the light-harvesting chlorophyll a/b-protein complex (CP-a/b) and SDS complexed chlorophyll. From these results we conclude that the chlorophyll molecules in the reaction center antennae are relatively more hydrophobically associated than the molecules in the light-harvesting CP-a/b complex. The chlorophyll a of CP-a_u and the far red absorbing chlorophyll a fraction of CP-a₁ appear to be the most hydrophobically associated chlorophyll molecules.     

Seasonal Effects on Photosynthetic Electron Transport and Fluorescence Properties in Isolated Chloroplasts of Pinus silvestris

Chloroplasts were isolated from primary needles of 1-year-old seedlings and from secondary needles of a 20-year-old pine tree in a natural stand. In autumn the electron transport capacities of PSII, PSI and PS (II + I) decreased and the electron transport between PSII and PSI became inhibited in October in the 20-year-old tree. This inhibition lasted until May the following year. The partial reactions of PSI and PSII still showed low but fairly constant rates during the whole winter seedlings. Seasonal changes in the electron transport properties of 1-year-old showed the same general trends as observed in the 20-year-old tree, but the changes were less pronounced. However, in snow-covered seedlings the PSI-mediated electron transport and the electron transport from H₂O to NADP increased during the late winter when the seedlings were still covered by snow. The total chlorophyll content of the needles decreased in autumn and winter. Low temperature fluorescence ratios of F692/F680 and F726/F680 indicated more severe destruction of the chlorophyll a antennae closely associated with the two photosystems than of the light harvesting chlorophyll a/b complex. In this case, too, the changes were more pronounced in the 20-year-old tree than in the 1-year-old seedlings. The chlorophyll/P700 ratios indicated a more marked reduction in the reaction centre molecules during autumn than in the antennae chlorophyll molecules. The changes in electron transport and low temperature fluorescence properties which occurred during autumn and winter were mainly reversed during spring.     

Light-Harvesting Function in the Diatom Phaeodactylum tricornutum: I. Isolation and Characterization of Pigment-Protein Complexes

Three pigment-protein complexes were isolated from the marine diatom Phaeodactylum tricornutum (Bohlin) by treatment of thylakoid membrane fragments with 1% Triton X-100 at 4°C followed by centrifugation on sucrose density gradients. The major complex contains chlorophyll a, c₁, c₂, and the carotenoid fucoxanthin (chlorophyll a: c₁: c₂: fucoxanthin = 1.0: 0.09: 0.28: 2.22) bound to an apoprotein doublet of 16.4 and 16.9 kilodaltons. This complex accounts for >70% of the total pigment and 20 to 40% of the protein in the thylakoid membranes. Efficient coupling of chlorophyll c and fucoxanthin absorption to chlorophyll a fluorescence supports a light-harvesting function for the complex. A minor light-harvesting complex containing chlorophyll a, c₁, and c₂ but no fucoxanthin (chlorophyll a: c₁: c₂ = 1.0: 0.23: 0.26) was also isolated at Triton: chlorophyll a ratios between 20 and 40. These pigments are bound to a similar molecular weight apoprotein doublet. The third complex isolated was the P700-chlorophyll a protein, the reaction center of photosystem I, which showed characteristics similar to those isolated from other plant sources. The yield of the chlorophyll a/c-fucoxanthin complex was shown to respond strongly to changes in light intensity during growth, accounting for most of the changes in cellular pigmentation.     

A diatom light-harvesting pigment-protein complex : purification and characterization

A light-harvesting pigment-protein complex was isolated from the diatom Phaeodactylum tricornutum using the zwitterionic detergent CHAPS (3-[3-cholamidopropyl)dimethylammonio]-1-propanesulfonate). Detergent-solubilized membranes were fractionated by sucrose density gradient centrifugation into three components. The medium density fraction contained chlorophyll a, chlorophyll c, and fucoxanthin. This fraction was purified by DEAE-ion exchange chromatography, and contained chlorophyll a, chlorophyll c, and fucoxanthin in a molar ratio of 2.4:1.0:4.8. Fluorescence emission and excitation spectra of the isolated complex demonstrated that light energy absorbed by chlorophyll c and fucoxanthin was coupled to chlorophyll a fluorescence. Upon denaturation, the apoprotein yielded a polypeptide doublet at 17.5 to 18.0 kilodaltons which accounted for 30 to 40% of the toal membrane protein. These findings indicate that this pigment-protein complex is a major component of the diatom photosynthetic lammellae. The quantitative amino acid composition of the apoprotein was very similar to those reported for other membrane-bound pigment-protein complexes. Based on the protein to chlorophyll a ratio of 7700 grams protein per mole chlorophyll a for the complex, each apoprotein molecule contains, to the nearest integer, two chlorophyll a, one chlorophyll c, and five fucoxanthin molecules. Polyclonal antibodies raised against the 17.5 to 18.0 kilodaltons apoprotein showed a monospecific reaction with only the 17.5 to 18.0 protein zone from denatured P. tricornutum membranes as well as to the nondenatured pigment-protein complex. It appears that this complex is common to other diatom species.     

CHARACTERIZATION OF PHOTOSYSTEM I-ASSOCIATED POLYPEPTIDES FROM THE CHLOROPHYLL b-RICH ALGA TETRASELMIS SPP. (PLEURASTROPHYCEAE) AND OTHER CHLOROPHYTE ALGAE1

The phylogenetic distribution of photosystem I-associated polypeptides was assessed by immunoblotting algal thylakoid membrane polypeptides with antisera generated against the P700-chlorophyll a protein (CC I) and a photosystem I light-harvesting chlorophyll-protein (LHC Ib). Polypeptides cross-reacting with the CC I apoprotein were found in 20 species representing four classes of unicellular algae. Polypeptides sharing antigenicity with spinach LHC Ib were observed only in algal species containing chlorophyll b. Tetraselmis spp. (Pleurastrophyceae), rich in chlorophyll b (Chl a:b 1.2), exhibited marked heterogeneity in the composition of their CC I and LHC Ib cross-reactive polypeptides. When immunoblotted with antisera against CC I, all Tetraselmis clones examined exhibited a 25-kD polypeptide in greater abundance than the 58-kD CC I apoprotein characteristic of higher plants and other green algal thylakoids. Three Tetraselmis clones (RG 6, RG 11, and RG 12) exhibited an 81-kD polypeptide with strong antigenicity toward the LHC Ib antisera, in contrast to the 17- to 24-kD cross-reactive polypeptides found in spinach, green algae, and one Tetraselmis clone (RG 5). Associated with the unique photosystem I polypeptide composition in Tetraselmis spp., Chl: P700 ratios for the group are 2–5 times greater than those observed for higher plants or other green algae. The chlorophyll b enrichment, unusual composition of photosystem I cross-reactive polypeptides, and heterogeneity of these polypeptides within isolates of Tetraselmis might make this genus useful for investigations of the functional organization of chlorophyll b in light-harvesting systems. These features also support the view of an alternative phyletic origin for the Pleurastrophyceae.     

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     

Presence of the Photoactive Reaction-Center Chlorophyll of PSI (P700) in Dark-Grown Cells of a Chlorophyll-Deficient Mutant of Chlorella kessleri

Compositions of pigments and polypeptides of pale green membranesthat had been isolated from dark-grown cells of a chlorophyll-deficientmutant of Chlorella kessleri were investigated. They containedChl a in a level corresponding to about 1% of that present inthe thylakoid membranes isolated from autotrophically grownwild-type cells and a trace amount of chlorophyllide a, butneither Chl b nor carotenoids. The polypeptide profile of themutant membranes was similar to that of membranes isolated fromwild-type cells that were grown in the dark. Neither the chlorophyll-bindingsubunits of PSI nor the apoproteins of LHCP were detected bySDS-PAGE and immunoblot analysis. However, the light-minus-darkdifference spectrum of the mutant membranes revealed the presenceof the reaction-center chlorophyll of PSI (P700) at a molarratio of 190 chlorophyll (Chl a plus Chlide a) per P700. P700was more stable than Chl a and Chlide a in the light so thatprolonged illumination led to a decline in the Chl/P700 ratioto 24. The initial rate of P700 photooxidation in the mutantmembranes was comparable to that in CP1 isolated from the dark-grownwild-type cells. Under illumination with strong light, the initialrate was decreased in parallel to the decrease in Chl/P700 ratio.The results suggest that most of Chi present in the mutant membranescan transfer excitation energy to P700. (Received March 13, 1998; Accepted August 7, 1998)     

Molecular arrangement of pigment-protein complex of photosystem 1

The circular dichroism (CD) method was applied to study the molecular organization of P700, antenna chlorophyll and protein of photosystem 1 complexes (CP1), isolated from chloroplasts under mild treatment with Triton X-100. Analysis of CD spectra and protein: chlorophyll: P700 ratios for CP1 complexes that were different in their chlorophyll content indicate that CP1 preparations can be considered as a mixture of CP1-RC, containing P700 (10–20%), and CP1-LH without P700 (80–90%). Both types of complexes contain approximately 25 chlorophyll molecules, and the destruction of their spatial organization with detergents represents a cooperative transition. The rate of chlorophyll destruction in CP1-LH is much higher than that in CP1-RC. In both complexes a 65 kDa polypeptide predominates, whose secondary structure (typical for / proteins) is stable to Triton X-100 and does not depends on the chlorophyll content. Chlorophyll seems to be grouped in clusters (5–7 molecules) in the hydrophobic cores of 2–3 parallel / domains of the 65 kDa protein. Only one of the clusters in CP1-RC includes P700; on P700 photooxidation the change of its interaction with the nearest pigment environment results in a complicated shape of the light-induced CD spectra.Abbreviations PS1 photosystem 1 - CP1 pigment-protein complex of PS1 - Chl chlorophyll a - CP1-140 CP1 with ratio Ch1:P700 140 - RC reaction center - LH light-harvesting pigment - CP1-RC CP1, containing P700 - CP1-LH CP1 without P700 (containing LH) - CD circular dichroism - SDS sodium dodecyl sulfate Dedicated to Prof. L.N.M. Duysens on the occasion of his retirement     

Effects of Frost Hardening and Dehardening on Photosynthetic Electron Transport and Fluorescence Properties in Isolated Chloroplasts of Pinus silvestris

Photosynthetic electron transport and low-temperature fluorescence emission properties have been analyzed in isolated chloroplasts during the course of frost hardening and dehardening of Pinus silvestris L. Both the partial electron-transport reactions (H₂O DPIP and Asc./DPIP NADP) and the overall electron transport (H₂O — NAPD) showed decreasing capacities during the course of hardening. Upon exposing the plants to ?5°C and high irradiance a block in the electron-transport chain between the two photosystems developed, whereas the partial reactions still showed activities. The decrease in activity of PSl was accompanied by a decrease in P700 content, as determined by light oxidation of P700, which indicates a correlation between the two changes. Hardening also induced changes in the in vivo chlorophyll organization. During the course of hardening the fluorescence emission bands F692 and F726 decreased relative to F680. These changes were more pronounced if the plants were treated in high than in low irradiance. This suggests a greater destruction of the chlorophyll antennae in close association with the two photoreactions than in the so-called light-harvesting chlorophyll a/b antenna. During dehardening basically the reverse of the changes observed during hardening occurred. The recovery of secondary needles was complete, whereas primary needles only partly recovered.     

Subunit organization of PSI particles from brown algae and diatoms: polypeptide and pigment analysis

P700 enriched fractions were isolated from two brown algae and one diatom using sucrose density centrifugation after digitinin solubilization. They had a Chl a/P700 ratio of about 250 to 375 according to the species, they were enriched in long-wavelength absorbing Chl a and exhibited a fluorescence emission maximum at 77 K near 720 nm. They all presented a major polypeptide component at 66±2 kDa, but their polypeptide composition was rather complex and somewhat different from one species to another. Further solubilization with dodecylmaltoside of those native PSI particles allowed the separation of two or three fractions. The lightest, xanthophyll-rich, fraction was identified to be a light-harvesting complex. It contained no P700 and had a major polypeptide of molecular weight near 20 kDa (at the same molecular weight than the respective LH native fraction of each species) and exhibited a 77 K peak fluorescence emission at 685 nm. The other fractions were enriched in P700 and almost entirely depleted in xanthophylls. When two of them are present, they both exhibited a major polypeptide at 66±2 kDa and were totally devoid of the LH polypeptide, but the two fractions widely differed one from another in the abundance and molecular weight of the other polypeptide components. The most purified of these two fractions presented a composition similar to PSI core complex from green plants.Abbreviations LH light-harvesting - LHCII light-harvesting complex II of green plants - P700 reaction center chlorophyll of PSI     

Preliminary phylogenetic analysis of plastid-encoded genes from an anomalously pigmented dinoflagellate Gymnodinium mikimotoi (Gymnodiniales, Dinophyta)

We cloned and sequenced three plastid-encoded genes, psbA (encoding D1 protein), psaA (encoding P700 chlorophyll a apoprotein) and the small-subunit ribo-somal RNA (pl-SSU rRNA) from an anomalously pigmented dinoflagellate, Gymnodinium mikimotoi Miyake et Kominami ex Oda, with a plastid containing 19′-hexanoyloxyfucoxanthin, 19′-butanoyloxyfucoxanthin and fucoxanthin instead of peridinin as the major carot-enoids. Molecular phylogenetic trees based on the deduced amino acid sequences of D1 and P700 chlorophyll a apoprotein and nucleotide sequence of pl-SSU rRNA were then constructed separately. In the D1 tree, G. mikimotoi and typically pigmented dinofl age Nates harboring a peridinin type plastid were monophyletic and G. mikimotoi was positioned most basally within the dinoflagellate lineage. The dinoflagellate lineage was the sister group of heterokonts and the dinoflagellates/heterokonts lineage was clustered with the rhodophytes/cryptophyte lineage. In the P700 chlorophyll a apoprotein phylogenetic tree, G. mikimotoi was clustered with a rhodo-phyte, a cryptophyte and a heterokont. In the pl-SSU rRNA tree, G. mikimotoi and haptophytes constituted a monophyletic group associated with rhodophytes and heterokonts. These results, derived from the three phylogenetic analyses, support the hypothesis that the plastid of G. mikimotoi belongs to the rhodoplast lineage. Although we have previously demonstrated that D1 from peridinin type dinofl age Nates lacks a ‘C-terminus extension’ (which should be removed by proteolytic cleavage from the D1 precursor), the D1 from G. mikimotoi revealed a C-terminus extension that is different from those of other photosynthetic organisms with respect to the length of the amino acid residues.     

Multiple forms of chlorophyll-protein complexes from a thermophilic cyanobacterium Synechococcus sp

Eight chlorophyll-proteins were resolved from the thylakoid membranes, or digitonin particles, of a thermophilic cyanobacterium Synechococcus sp. by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Six chlorophyll-proteins with slower electrophoretic mobilities were shown to be P700-chlorophyll a-protein complexes (CP1), whereas faster-moving proteins (CP2) were related to photosystem 2. Extraction of CP1 complexes from the membranes with different detergent/chlorophyll ratios and reelectrophoresis of extracted CP1 complexes indicated that the chlorophyll-proteins are closely interrelated with each other; any CP1 complex could be transformed to other CP1 complexes with faster electrophoretic mobilities. This, together with the Ferguson plot and the polypeptide composition, showed that six CP1 complexes are different in terms of polypeptide composition, oligomerization, SDS-binding, or conformation of the proteins but represent, in the order of increasing electrophoretic mobility, increasing degree of modification of the native P700-chlorophyll a-protein.     

Chlorophyll Composition in an Isolated Chlorophyll a-Protein Complex of Photosystem I

A P700-chlorophyll a-protein complex, solubilized by the detergent Triton X-100, has been isolated by hydroxyl apatite column chromatography. The chlorophyll composition was determined by thin-layer chromatography and spectrofluorimetric analysis. This photosystem I reaction centre complex, prepared at pH 7, contained pheophytin a and P700 in a ratio of 2/1, high enough to account for a composition similar to that in the reaction centre of photosynthetic bacteria. Prepared at pH 9, the same ratio was 0.2/1, which excludes pheophytin a from having the same function as that of bacterio-pheophytin in the photosynthetic bacteria.     

Reorganization of Thylakoid Components during Chloroplast Development in Higher Plants after Transfer to Darkness : Changes in Photosystem I Unit Components, and in Cytochromes

It was shown earlier that in etiolated bean (Phaseolus vulgaris, var. red kidney) leaves exposed to continuous light for a short time and then transferred to darkness a reorganization of their photosystem II (PSII) unit components occurs. This reorganization involves disorganization of the light-harvesting complex of PSII (LHC-II), destruction of its chlorophyll b and the 25 kilodalton polypeptide, and reuse of its chlorophyll a for the formation of additional, small in size, PSII units (Argyroudi-Akoyunoglou, Akoyunoglou, Kalosakas, Akoyunoglou 1982 Plant Physiol 70: 1242-1248). The present study further shows that parallel to the PSII unit reorganization a reorganization of the PSI unit components also occurs: upon transfer to darkness the 24, 23, and 21 kilodalton polypeptides, components of the light-harvesting complex of PSI (LHC-I), are decreased, the 69 kilodalton polypeptide, component of the chlorophyll a-rich P700-protein complex (CPI), is increased and new smallsized PSI units are formed. Concomitantly, the cytochrome f/chlorophyll and the cytochrome b/chlorophyll ratios are gradually increased. This suggests that the concentration of the electron transport components is also modulated in darkness to allow for adequate electron flow to occur between the newly synthesized PSII and PSI units.     

Inhibition of photosynthetic electron transport and formation of inactive chlorophyll in winter stressed Pinus silvestris

Kinetics of fluorescence at room temperature, electron transport and photooxidation of P700 and cytochrome f have been studied in chloroplasts isolated from active and winter stressed Pinus silvestris. The winter stress induced block in the electron transport chain between the two photosystems is close to the site of plastoquinone, since winter stress and DCMU caused the same type of inhibition of the reoxidation of the primary electron acceptor Q of photosystem II. No winter inhibition of the electron transport between cytochrome f and P700 was observed. Time course studies of P700 photooxidation in chloroplasts of active and winter stressed pine have shown that the photosynthetic unit size must be about equal in the two types of chloroplasts. An apparent increase of the photosynthetic unit size was induced by winter stress, as revealed by the high chlorophyll/P700 ratio of winter stressed pine. The phenomenon is explained by the formation of photosynthetically inactive chlorophyll. Low-temperature fluorescence emission spectra were recorded when either chlorophyll a (433 nm) or chlorophyll b (477 nm) were preferentially excited. Winter stress induced the formation of a chlorophyll a fraction emitting at 673 nm. This chlorophyll is most likely derived from the chlorophyll a antennae of the two photosystems, and it probably contributes to the photosynthetically inactive pool of chlorophyll in winter stressed pine. The light harvesting chlorophyll a/b complex is relatively resistant to winter stress.     

The P700-chlorophyll a-protein. Isolation and some characteristics of the complex in higher plants

A P700-chlorophyll a-protein complex has been purified from several higher plants by hydroxylapatite chromatography of Triton X-100-dissociated chloroplast membranes. The isolated material exhibits a red wavelength maximum at 677 nm, major spectral forms of chlorophyll a at 662, 669, 677, and 686 nm, a chlorophyll/P700 ratio of $\text{40–45}\text{1}$, and contains only chlorophyll a and β-carotene of the photosynthetic pigments present in the chloroplast. The spectral characteristics and composition of the higher plant material are homologous to those of the P700-chlorophyll a-protein previously isolated from blue-green algae; however, unlike the blue-green algal component, cytochromes f and b₆ are associated with the higher plant material. Evidence is presented that a chlorophyll a-protein termed “Complex I” which can be isolated from sodium dodecyl sulfate extracts of chloroplast membranes is a spectrally altered form of the eucaryotic P700-chlorophyll a-protein. The isolation procedure described in this paper is a more rapid technique for obtaining the heart of photosystem I than presently exists; furthermore, the P700 photooxidation and reduction kinetics in the fraction are improved over those in other isolated components showing the same enrichment of P700. It appears very probable that the heart of photosystem I is organized in the same manner in all chlorophyll a-containing organisms.