Formation of Chlorophyll-Protein Complexes in Greening Cucumber Cotyledons in Light and then in Darkness

The changes in chlorophyll-protein complexes (CPs) in cucumbercotyledons during illumination and subsequent dark incubationwere studied by SDS-polyacrylamide gel electrophoresis. Whenetiolated cucumber seedlings were illuminated, chlorophyll wassynthesized and CPs were formed. In the early phase of greening(6 h of illumination), light-harvesting chlorophyll a/b-proteincomplex (LHCP) was the main GP. As the greening proceeded, P700chlorophyll a-protein complex (CP1) accumulated. When 6-h illuminatedseedlings were transferred to darkness, CP1 accumulated concomitantlywith a decrease in LHCP without new chlorophyll synthesis. Thechanges in the amounts of CPs in the dark became smaller withthe progress of greening and were not observed after 72 h ofillumination. These changes were confirmed by examining thechlorophyll/P700 ratio and the low temperature absorption spectrumof cotyledons. These results suggest that in the early phaseof greening, CPs were unstable and their chlorophyll moleculeseasily exchanged with those of other kinds of CPs. (Received October 14, 1982; Accepted December 1, 1982)     

Appearance of Chlorophyll-Protein Complexes in Greening Barley Seedlings

The sequential appearance of chlorophyll-protein complexes (CP)in greening barley leaves was studied by an improved methodof SDS-polyacrylamide gel electrophoresis (PAGE). Solubilizedthylakoid membranes were purified using a sucrose step gradientand CPs were separated by PAGE with low concentrations of SDSin solubilizing and reservoir buffers. At 10 min after the onsetof illumination, a chlorophyll-protein complex (CPX) was detected.It was a labile CP, its chlorophyll (Chl) being easily releasedfrom the apoprotein during electrophoresis. The P700-chlorophylla/b-protein complex (CPl) appeared after 45–60 min ofillumination together with P700 activity. Light-harvesting chlorophylla/b-protein complex (LHCP) began to accumulate at 2.5 h withthe beginning of Chl b synthesis. In some cases a small amountof CPa could be detected after 6 h of greening. The time-differencespectrum between homogenates of leaves illuminated for 30 and60 min had an absorbance maximum at 677 nm, showing that a redshift indicative of CPl formation began soon after completionof the Shibata shift. The time-difference spectrum between 3.5-hand 4.0-h illuminated leaves resembled the absolute spectrumof fully greened leaves, indicating that at this stage, spectralcomponents were being synthesized at the same ratio at whichthey exist in fully greened tissues. Both absolute and time-differencespectral data supported the SDS-PAGE results. (Received February 27, 1985; Accepted May 8, 1985)     

Developmental Changes in Amounts of Thylakoid Components in Plastids of Barley Leaves

Changes in the amounts of several components of the photosyntheticelectron-transport system during greening of etiolated barleyleaves were studied on a "per plastid" basis. P700 and Q_A, whichwere initially absent from etioplasts, appeared 2 h after thestart of illumination in complete complexes of PS I and PS II,respectively. From 6 h, they increased rapidly in amount witha constant stoichiometric ratio of 1:1. Amounts of Cyt f, Cytb₆, Cyt b-559 and FeS, initially present in etioplasts at levelsthat were one-third to half of those in mature chloroplasts,also increased rapidly after 6 h of illumination. The molarratio of Cyt f, Cyt b₆ and Cyt b-559 was the same in etioplastsand in mature chloroplasts, namely 1:2:2. After 4 h of illumination,levels of FeS increased at nearly the same rate as those ofthe PS I complex. The increase in levels of all components wasmarked after 6 h of illumination, probably due to the energysupplied by developing plastids that had just become photosyntheticallycompetent. The results are discussed in relation to the timeof appearance of chlorophyll-protein complexes and photochemicalactivities. ¹ Present address: Department of Botany, Faculty of Science,Kyoto University, Kyoto, 606-01 Japan.     

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

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

Chlorophyll-protein complex composition during chloroplast development: A species comparison

Barley, maize, pea, soybean, and wheat exhibited differences in chlorophyll a/b ratio and chlorophyll-protein (CP) complex composition during the initial stages of chloroplast development. During the first hours of greening, the chlorophyll a/b ratios of barley, pea, and wheat were high (a/b8) and these species contained only the CP complex of photosystem I as measured by mild sodium dodecyl sulfate polyacrylamide gel electrophoresis. A decrease in chlorophyll a/b ratio and the observation of the CP complexes associated with photosystem II and the light-harvesting apparatus occurred at later times in barley, pea, and wheat. In contrast, maize and soybean exhibited low chlorophyll a/b ratios (a/b<8) and contained the CP complexes of both photosytem I and the light-harvesting apparatus at early times during chloroplast development. The species differences were not apparent after 8 h of greening. In all species, the CP complexes were stabilized during the later stages of chloroplast development as indicated by a decrease in the percentage of chlorophyll released from the CP complexes during detergent extraction. The results demonstrate that CP complex synthesis and accumulation during chloroplast development may not be regulated in the same way in all higher plant species.Abbreviations Chl chlorophyll - CP chlorophyll-protein - CPI P700 chlorophyll-a protein complex of photosystem I - CPa electrophoretic band that contains the photosystem II reaction center complexes and a variable amount of the photosystem I light-harvesting complex - LHC the major light-harvesting complex associated with photosystem II - PSI photosystem I - PSII photosystem II - SDS sodium dodecyl sulfate - SDS-PAGE sodium dodecyl sulfate polyacrylamide gel electrophoresis Cooperative investigations of the United States Department of Agriculture, Agricultural Research Service, and the North Carolina Agricultural Research Service, Raleigh, NC 27695-7601. Paper No. 10335 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, NC 27695-7601.     

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.     

Chlorophyll b-Deficient Mutants of Rice: II. Antenna Chlorophyll a/b-Proteins of Photosystem I and II

Chlorophyll-protein complexes of the wild type and 16 strainsof chlorina mutants of rice were investigated by gel electrophoresis.An antenna chlorophyll a/b-protein of photosystem II (LHC-II)was present in reduced amounts in Type II chlorina mutants whichhave the chlorophyll a/b ratios of 10–15, and was totallyabsent from Type I chlorina mutants which lack chlorophyll b.Another antenna chlorophyll-protein of photosystem I (LHC-I)containing two polypeptides of 20 and 21 kDa was also presentin the Type II mutants but not in the Type I mutants. The polypeptideprofiles of the thylakoid membranes indicate that Type I mutantslack both the 20 and 21 kDa polypeptides, whereas the abundanceof the two polypeptides relative to the CPI apoprotein in theType II mutants is comparable with that in the wild type. Itis concluded that the 20 and 21 kDa polypeptides are both relatedto LHC-I and are normally synthesized and accumulated in theType II mutants. (Received June 6, 1985; Accepted August 6, 1985)     

Expression of protein complexes and individual proteins upon transition of etioplasts to chloroplasts in pea (Pisum sativum)

The protein complexes of pea (Pisum sativum L.) etioplasts,etio-chloroplasts and chloroplasts were examined using 2D BlueNative/SDS–PAGE. The most prominent protein complexesin etioplasts were the ATPase and the Clp and FtsH proteasecomplexes which probably have a crucial role in the biogenesisof etioplasts and chloroplasts. Also the cytochrome b₆f (Cytb₆f) complex was assembled in the etioplast membrane, as wellas Rubisco, at least partially, in the stroma. These complexesare composed of proteins encoded by both the plastid and nucleargenomes, indicating that a functional cross-talk exists betweenpea etioplasts and the nucleus. In contrast, the proteins andprotein complexes that bind chlorophyll, with the PetD subunitand the entire Cyt b₆f complex as an exception, did not accumulatein etioplasts. Nevertheless, some PSII core components suchas PsbE and the luminal oxygen-evolvong complex (OEC) proteinsPsbO and PsbP accumulated efficiently in etioplasts. After 6h de-etiolation, a complete PSII core complex appeared with40% of the maximal photochemical efficiency, but a fully functionalPSII was recorded only after 24 h illumination. Similarly, thecore complex of PSI was assembled after 6 h illumination, whereasthe PSI–light-harvesting complex I was stably assembledonly in chloroplasts illuminated for 24 h. Moreover, a batteryof proteins responsible for defense against oxidative stressaccumulated particularly in etioplasts, including the stromaland thylakoidal forms of ascorbate peroxidase, glutathione reductaseand PsbS.     

Immunological Quantification of Proteins Related to Light-Harvesting Chlorophyll a/b Protein Complexes of the Two Photosystems in Rice Mutants Totally and Partially Deficient in Chlorophyll b

Ten rice chlorina mutants of Type I, which totally lack chlorophyllb and hence are unable to synthesize light-harvesting chlorophylla/b protein complexes of photosystem II (LHC-II), containedmRNA for proteins related to LHC-II. Immunoblotting with anantiserum, which had been raised against the 24 and 25 kDa apoproteinsof LHC-II and found to cross-react with the 26 kDa protein ofLHC-II and the 20 and 21 kDa apoproteins of light-harvestingchlorophyll a/b protein complexes of photosystem I (LHC-I),revealed that all the five proteins related to LHC-Iand LHC-IIwere present in reduced amounts in the Type I mutants. ThreeType HA mutants, which have a chlorophyll a/b ratio of 10, weremore abundant in the apoproteins, while three Type IIB mutantswith the ratio of 15 were heterogeneous in terms of the apoproteincontent. All the chlorina mutants contained less P700 comparedwith the wild type rice, but were relatively more abundant inthe LHC-I proteins than the LHC-II proteins. The results showthat all the rice chlorina strains are mutants of chlorophyllb synthesis and the deficiency of chlorophyll b differentlyaffects accumulation of the apoproteins of LHC-I and LHC-II.To balance light absorption between the two photosystem, lossof LHC-II is partly counter-balanced by a decrease in the numberof PSI complexes in the mutants. (Received January 21, 1988; Accepted April 28, 1988)     

Formation of Chlorophyll-Protein Complexes during Greening 1. Distribution of Newly Synthesized Chlorophyll among Apoproteins

The relationship between the accumulation of Chl and the apoproteinsof the light-harvesting Chl a/b-protein complex of PS II (LHCII)during the greening of cucumber cotyledons was studied. LHCIIapoproteins were not detected in etiolated cotyledons. Uponillumination, Chl a was formed as a result of photoconversionof protochlorophyllide (Pchlide) which had accumulated in thedark. During the lag period that preceded the accumulation ofChl, a small amount of LHCII apoproteins appeared. The amountof LHCII apoproteins increased with increases in levels of Chlb, though somewhat more rapidly during the first 10 h of greening.Treatment with benzyladenine (BA) or levulinic acid (LA) wasused to vary the supply of Chl a for apoproteins by promotingor inhibiting the synthesis of Chl a, respectively. LA decreasedbut BA increased the rate of accumulation of Chl b and LHCIIapoproteins. Only small amounts of Chl b and LHCII apoproteinswere formed under intermittent illumination. However, in thepresence of chloramphenicol (CAP), which inhibits the synthesisof plastome-coded proteins including apoproteins of the P700-Chla-protein complex (CP1) and a Chl a-protein complex of PS II(CPa), we observed the accumulation of Chl b and LHCII apoproteins,both of which are of nuclear origin. During incubation in thedark after intermittent exposure to light, CAP alone allowedneither destruction nor accumulation of Chl b and LHCII apoproteins,but it did enhance the effect of CaCl₂ in inducing both Chlb and these apoproteins. These results can be explained by assumingthat apoproteins of CP1 and CPa have a higher affinity for Chla than do LHCII apoproteins. When the availability of Chl ais limited, these apoproteins compete with one another for Chla, with the resultant preferential formation of CP1 and CPa.However, when the supply of Chl a becomes large enough for saturationof apoproteins of CP1 and CPa, some of the Chl a is incorporatedinto LHCII apoproteins either directly or after conversion toChl b. Thus, the formation of different Chl-protein complexes(CPs) is regulated by the relative rates of synthesis of Chla and apoproteins and by differential affinities of the apoproteinsfor Chl a. ⁴Present address: Kyowa Hakko Co., Ltd., 4041, Ami-machi, Inashiki,Ibaraki, 300-03 Japan (Received September 14, 1989; Accepted April 26, 1990)     

Relationship between Photosynthesis and Chlorophyll Content during Leaf Senescence of Rice Seedlings

Photosynthetic oxygen evolution, chlorophyll contents and chlorophylla /b ratios of 3rd to 6th leaves of rice seedlings were measuredto examine whether or not inactivation of photosynthesis duringsenescence is related to loss of chlorophyll. Photosyntheticactivity decreased more rapidly than chlorophyll content duringleaf senescence; as a result, the lower the leaf position, thelower was the rate of oxygen evolution determined on the basisof chlorophyll. Chlorophyll ab ratio also decreased with advancingsenescence. Electrophoretic analysis revealed that the declinein chlorophyll ab ratio is due to more rapid degradation ofthe reaction center complexes than light-harvesting chlorophyllab proteins of photosystem II and that the photosystem I reactioncenter disappears in parallel with the inactivation of photosynthesis.A simple method was developed to estimate the amounts of chlorophylla associated with the reaction center complexes of the two photosystemsfrom the total chlorophyll contents and chlorophyll ab ratiosof leaves. Rates of oxygen evolution, determined on the basisof chlorophyll a bound to the reaction center complexes, remainedconstant throughout the course of senescence. Thus, inactivationof photosynthesis is closely related with loss of the reactioncenter complexes during leaf senescence of rice seedlings. Theresults suggest that loss of photosynthesis is mainly causedby loss of a functional unit of photosynthesis or by a decreasein the number of whole chloroplasts. (Received April 22, 1987; Accepted August 13, 1987)     

Pigment Composition of Chlorophyll-Protein Complexes Isolated from the Green Alga Bryopsis maxima

SDS-solubilized thylakoid membranes of Bryopsis maxima showeda similar pattern to those of higher plants in SDS-poIyacrylamidegel electrophoresis. Absorption spectra and pigment compositionof both CP1 and CPa bands were similar to those of higher plantsand other algae. Five bands containing chlorophyll (Chl) b weredivided into three categories; a group of major light-harvestingChl a/b-protein complexes (LHCP 1, LHCP 2 and LHCP 3), a minorLHCP (LHCP 3') and a photosystem I complex (CP1a). LHCP 1, thehigh molecular form, showed the lowest Chl a/b ratio among theLHCPs, and contained only xanthophylls as carotenoids. LHCP2, LHCP 3 and LHCP 3' bands contained xanthophylls and carotene.Carotenoid composition of LHCP 3' was different from that ofthe major LHCPs. CP1a band contained a considerable amount ofsiphonaxanthin and siphonein. (Received May 24, 1985; Accepted December 13, 1985)     

The light-harvesting system of Euglena gracilis during the cell cycle

The apoproteins of the light-harvesting chlorophyll-protein complexes LHCI and CP29 (apparent molecular weights of 27 kDa and 29 kDa, respectively) of Euglena gracilis were identified immunologically. Both complexes are present in the thylakoids of autotrophically cultured Euglena cells during the whole cell cycle. The relative amount of each apoprotein tends to increase towards the end of the cell cycle. The light-harvesting chlorophyll-protein complex of photosystem II, LHCII, of E. gracilis contains chlorophyll a, chlorophyll b, neoxanthin, diadinoxanthin and beta-carotene. Its chlorophyll a/b ratio is about 1.7 during the whole cell cycle. About 9 h after cell division the ratio of diadinoxanthin to chlorophyll a is doubled for a time of 3–4 h. The relevance of this increase during one developmental stage is discussed in relation to the insertion and-or assembly of newly synthesized LHCII.Abbreviations LHCP light-harvesting chlorophyll-protein complex - PS photosystem This research was partly supported by the Deutsche Forschungsge meinschaft.     

Evidence from Crosslinking for a Close Association of the Extrinsic 33 kDa Protein with the 9.4 kDa Subunit of Cytochrome b 559 and the 4.8 kDa Product of the psb I Gene in Oxygen-Evolving Photosystem II Complexes from Spinach

Oxygen-evolving photosystem II complexes from spinach, whichlack light-harvesting chlorophyll a/b proteins, were treatedwith a bifunctional crosslinking reagent, hexamethylene-diisocyanate.Identification of crosslinked proteins with antisera raisedagainst various constituent proteins of the oxygen-evolvingPS II complex showed that the extrinsic 33 kDa protein is locatedless than 11 Å from the 9.4 kDa subunit of cytochromeb 559 and the 4.8 kDa product of psb I gene. (Received October 14, 1991; Accepted February 6, 1992)     

Characterization of new strains of nonphotosynthetic mutants of Chlamydomonas reinhardtii I. Fluorescence, photochemical activities, chlorophyll-protein complexes

Thirty-six new strains of nonphotosynthetic mutants of Chlamydomonasreinhardtii, which had been induced by UV irradiation then screenedphotographically for strong chlorophyll fluorescence of theircolonies, were characterized with respect to pigment contents,photochemical activities of Hill and Mehler reactions and chlorophyllfluorescence induction, and by SDS-polyacrylamide gel electrophoresisof the chlorophyllprotein complexes. Eight strains did not show any Photosystem II activity and fiveshowed only very weak activity. Analysis of the chloroplastmembranes of ten of these strains showed that all containedboth complexes CP I and CP II. In the case of one of these mutants,Fl 50, which was totally unable to perform the Hill reactionfrom H₂O, addition of DPC restored about 25% of the DCIP photoreductionactivity. This could be interpreted tentatively in terms ofan impaired accessibility of the Photosystem II centers to electrondonors and acceptors. Ten other mutants showed the following anomalies: no PhotosystemI activity, lack of complex CP I, and higher chlorophyll fluorescenceyield and lower Chl a/Chl b ratio than the wild type. Thesefeatures appeared to be related. (Received February 8, 1979; )     

Regulation of Electron Transport Composition in Cyanobacterial Photosynthetic System: Stoichiometry among Photosystem I and II Complexes and Their Light-Harvesting Antennae and Cytochrome b6/fComplex

This study was done to confirm our previous observation withthe pattern of changes in electron transport composition inducedby an imbalance of the electron transport state. Contents ofphotosystem (PS) I and II complexes and their antennae and Cytb₆/f complex were determined for systems of cyanobacterium SynechocystisPCC 6714 of different PS I/PS II ratios. The results indicatedthat (1) the observed changes in the PS I/PS II ratio are not-dueto regulation of the activities of the respective PS's but tochanges in their contents, (2) the molar ratio between PS IIand Cyt b₆/f complexes was fairly constant when marked changesoccurred in the PS I content, and (3) the PS II and Cyt b₆/fcontents per cell remained fairly constant while the PS I contentchanged markedly. These findings agree with our previous observationwith autotrophic cells of Anacystis nidulans Tx 20 and supportour argument that in cyanobacterial and red algal electron transportsystems, the content of the terminalcomponent(s), such as PSI complex, is regulated in order to maintain a balance betweenthe electron influx by PS II action to the system and the effluxby PS I action from it. (Received June 3, 1987; Accepted September 20, 1987)     

Isolation and Characterization of a Light-Harvesting Chlorophyll a/b Protein Complex Associated with Photosystem I

A chlorophyll a/b protein complex has been isolated from a resolved native photosystem I complex by mildly dissociating sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The chlorophyll a/b protein contains a single polypeptide of molecular weight 20 kilodaltons, and has a chlorophyll a/b ratio of 3.5 to 4.0. The visible absorbance spectrum of the chlorophyll a/b protein complex showed a maximum at 667 nanometers in the red region and a 77 K fluorescence emission maximum at 681 nanometers. Alternatively, by treatment of the native photosystem I complex with lithium dodecyl sulfate and Triton, the chlorophyll a/b protein complex could be isolated by chromatography on Sephadex G-75. Immunological assays using antibodies to the P₇₀₀-chlorophyll a-protein and the photosystem II light-harvesting chlorophyll a/b protein show no cross-reaction between the photosystem I chlorophyll a/b protein and the other two chlorophyll-containing protein complexes.     

Photocontrol of the Accumulation of Plastid Polypeptides during Greening of Tomato Cotyledons : Potentiation by a Pulse of Red Light

A pulse of red light acting through phytochrome accelerates the formation of chlorophyll upon subsequent transfer of dark-grown seedlings to continuous white light. Specific antibodies were used to follow the accumulation of representative subunits of the major photosynthetic complexes during greening of seedlings of tomato (Lycopersicon esculentum). The time course for accumulation of the various subunits was compared in seedlings that received a red light pulse 4 h prior to transfer to continuous white light and parallel controls that did not receive a red light pulse. The light-harvesting chlorophyll-binding proteins of photosystem II (LHC II), the 33-kD extrinsic polypeptide of the oxygen-evolving complex (OEC1), and subunit II of photosystem I (psaD gene product) all increased in the light, and did so much faster in seedlings that received the inductive red light pulse. The red light pulse had no significant effect on the abundance of the small subunit of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco), nor on several plastid-encoded polypeptides: the large subunit of Rubisco, the β subunit of the CF₁ complex of plastid ATPase, and the 43- and 47-kD subunits of photosystem II (CP43, CP47). Subunits I (cytochrome b₆f) and III (Rieske Fe-S protein) of the cytochrome b₆f complex showed a small or no increase as a result of the red pulse. The potentiation of greening by a pulse of red light, therefore, is not expressed uniformly in the abundance of all the photosynthetic complexes and their subunits.     

Regulation of the Stoichiometry of Thylakoid Components in the Photosynthetic System of Cyanophytes: Model Experiments Showing that Control of the Synthesis or Supply of Chl a can Change the Stoichiometric Relationship between the Two Photosystems

Regulation of the assembly of the photosystem I (PS I) complexin response to the light regime in the photosynthetic systemof cyanophytes was studied in Synechocystis PCC 6714. The relationshipbetween the assembly of the PS I complex and synthesis of Chla was examined by model experiments in which synthesis of Chla was controlled by two inhibitors, gabaculine (GAB) and 2,2'-dipyridyl(DP). Both inhibitors caused a change to a lower ratio of PSI to PS II even under light that normally induces a high ratioof PS I to PS II. The change in stoichiometry induced by theseinhibitors was suppressed when protein synthesis was inhibitedby chloram-phenicol, similarly to the change in the stoichiometryinduced by light that excites mainly PS I (PS I light). Comparisonof the levels of PS I, PS II and Cyt b₆-f complexes per cellindicated that a selective suppression of the assembly of thePS I complex was induced by the inhibitors: the stoichiometricrelationship among PS I, PS II and Cyt b₆-f complexes was identicalto that induced by PS I light or white light of high intensity.GAB induced a decrease in size of the phycobilisome also, whileDP did not, similarly to PS I light. The results indicate thatthe ratio of PS I to PS II can be changed by the control ofsynthesis of Chl a. They also suggest that control of the synthesisor supply of Chl a probably exerted at site(s) in or after theprocess of the Mg-protoporphyrin branch, is involved in themechanism of regulation of the assembly of the PS I complexin cyanophytes. (Received September 7, 1989; Accepted November 20, 1989)