Effect of Supra-High Irradiation on the Photosynthetic System of the Cyanophyte Synechocystis PCC 6714

Stability of thylakoid components under supra-high irradiancewas studied with the cyanophyte Synechocystis PCC 6714. Theactivity of overall photosynthesis was quickly inactivated (T_1/2=20min) under supra-high irradiance (300 W m^–2, white light).In parallel with the inactivation of photosynthesis, QA in PSII was also inactivated. Both inactivations were acceleratedby chloramphenicol (CAP) addition. The reactivation of PS IIrequired weak irradiation and was suppressed by CAP. However,PS I measured as P700 was very stable. The level of PS I measuredas P700 was not significantly reduced by the irradiation for12 h even in the presence of CAP while the level of Cyt b₅₅₉,component of PS II, was decreased markedly. The function ofPS I before and after supra-high irradiation with CAP was examinedby comparing sizes of P700 oxidation induced by a short flash,by a continuous light, and by determination of O₂-and ferredoxin-reduction.No difference was observed in PS I actions before and afterthe irradiation treatment. These results indicate that the PSI complex is very tolerant of supra-high irradiation. However,the cells grown under supra-high irradiance contained much fewerPS I and PS II complexes than Cyt b₆–f complexes. Theformer levels were reduced to a half to one fourth of thosebefore growth while the level of Cyt b₆–f complex wasnot reduced so much. A possible mechanism for changes in thylakoidcomposition under supra-high irradiation was discussed. (Received February 16, 1991; Accepted June 12, 1991)     

Carotenoid photobleaching induced by photosystem II action in the membrane fragments of the blue-green alga Anabaena variabilis : Action of O2

Carotenoid photobleaching induced by photosystem II action wasstudied using membrane fragments of the blue-green alga Anabaenavariabilis. Special attention was paid to the action of O₂. Carotenoid photobleaching elicited by carbonyl cyanide m-chlorophenylhydrazone(CCCP) depended on O₂. However, the addition of H₂O₂, sodiumsilicotungstate or potassium ferricyanide (Ferri), an electronacceptor for reaction center II action, removed the O₂-dependency.These results indicate that O₂ acts as the electron acceptorfor this reaction. When both CGCP and Ferri were present, a short illumination(0.25 sec) caused a rapid photobleaching followed by a slowrecovery in the subsequent dark period. The spectrum of theabsorption decrease in the light was identical with that ofthe absorption increase in the subsequent dark, indicating thata reversible process is involved in the carotenoid photobleaching.The size in the dark recovery relative to the light bleachingbecame larger under anaerobic conditions and smaller under higherpartial pressure of O₂. The reuslts were interpreted as indicatingthat O₂ does not function in the primary process including areversible bleaching step, but is involved in the slow and irreversiblebleaching process. (Received April 3, 1978; )     

Excitation energy transfer between pigment system II units in blue-green algae

Efficiency in excitation energy transfer from closed to open reaction center II in blue-green and red algae was estimated by the method developed by Joliot and Joliot (C.R. Acad. Sci. (1964) 258, 4622–4625) after slight modification; the number of open reaction centers II was counted from the mean O₂ yield of repetitive short flashes.

The efficiency in energy transfer in Chlorella pyrenoidosa was the same in our measurement as that reported by Joliot and Joliot (0.55 ± 0.02). However, the values obtained with four blue-green algae and one red alga were very small, in a range of 0.00–0.07. The low efficiency was always obtained independently of the size of the apparent photosynthetic unit which was varied by growth conditions. Results indicated that pigment system II forms a unit in which only one reaction center II is operative.     

Regulation of Photosystem Stoichiometry in the Photosynthetic System of the Cyanophyte Synechocystis PCC 6714 in Response to Light-Intensity

Light-induced changes in stoichiometry among three thylakoidcomponents, PS I, PS II and Cyt b₆-f complexes, were studiedwith the cyanophyte Synechocystis PCC 6714. Special attentionwas paid to two aspects of the stoichiometric change; first,a comparison of the patterns of regulation in response to differencesin light-intensity with those induced by differences in light-quality,and second, the relationship between regulation of the stoichiometryand the steady state of the electron transport system. Resultsfor the former indicated that (1) the abundance of PS I on aper cell basis was reduced under white light at the intensityas high as that for light-saturation of photosynthesis, butPS I per cell was increased under low light-intensity, (2) PSII and Cyt b₆-f complexes remained fairly constant, and (3)changes in the abundance of PS I depended strictly on proteinsynthesis. The pattern was identical with that of chromaticregulation. For the second problem, the redox steady-statesof Cyt f and P700 under white light of various intensities weredetermined by flash-spectroscopy. Results indicated that (1)Cyt f and P700 in cells grown under low light-intensity [highratio of PS I to PS II (PS I/PS II)] were markedly oxidizedwhen the cells were exposed to high light-intensity, while theyremained in the reduced state under low light-intensity. (2)After a decrease in the abundance of PS I, most of P700 remainedin the reduced state even under high light-intensity, whilethe level of reduced Cyt f remained low. (3) Both Cyt f andP700 in cells of low PS I/PS II were fully reduced under lowlight-intensity, and Cyt f reduction following the flash wasrapid, which indicates that the turnover of PS I limits theoverall rate of electron flow. After an increase in the abundanceof PS I, the electron transport recovered from the biased state.(4) The redox steady-state of the Cyt b₆-f complex correlatedwell with the regulation of PS I/PS II while the state of thePQ pool did not. Based on these results, a working model ofthe regulation of assembly of the PS I complex, in which theredox steady-state of the Cyt b₆-f complex is closely relatedto the primary signal, is proposed. (Received August 2, 1990; Accepted December 10, 1990)     

Electron donor-specificity observed in photosystem I reactions of membrane fragments of the blue-green alga Anabaena variabilis and the higher plant Spinacea oleracea

Electron donating activities of plastocyanins and c-type cytochromesof various organisms for photosystem I reactions were studiedwith membrane fragments of the blue-green alga Anabaena variabilisand the higher plant Spinacea oleracea. In the Anabaena photosystem I reaction, basic but not acidicplastocyanin and c-type cytochromes acted as efficient electrondonors, while only acidic redox proteins were active in thespinach photosystem I reaction. The selective reactivity ofredox proteins in the two photosystem I reactions was observedwith both plastocyanin (or cytochrome) limited and saturatedconditions. These data support our previous observation that photosystemI of blue-green algae differs from those of other green plantswith respect to specificity to the proteinous electron donor(1). (Received August 17, 1971; )     

Pyrone derivatives: effective inhibitors of photosynthetic electron flow system

The inhibitory effects of the pyrone derivatives, 6-()-decenyl-2,3-dimethyl--pyrone(DDP) and 6-farnesyl-2,3-dimethyI--pyrone (FDP), on the photosyntheticelectron flow system was investigated using the blue-green algaAnabaena variabilis and the green alga Chlorella pyrenoidosa. Both reagents inhibited photosynthesis in intact cells; 50%inhibition occurred at 2.7 x 10^–5 M with DDP and at 4.3 lO^–6 M with FDP in Anabaena photosynthesis. The reagentssuppressed the photosystem II reaction [water to 2,6-dichlorophenolindophenol (DCIP)] of Anabaena membrane fragments, but werefar less inhibitory on the photo-system I reaction (DCIPH₂ tomethyl viologen). The kinetics of the fluorescence inductionindicated that the reagents do not block Q-reduction, but dosuppress the oxidation of reduced Q indirectly. Oxygen evolutionunder repetitive flashes at a low repetition rate (5 Hz) wasinsensitive to the reagents even at concentrations which inducedmore than 50% inhibition. These results are evidence that DDPand FDP inhibit the plastoquinone reaction by slowing down itsturnover rate. The advantages of pyrone derivatives are that they are inactivein the oxidation-reduction reaction and do not quench the fluorescenceof chlorophyll in vivo. (Received April 14, 1980; )     

The Photosynthetic Apparatus of Phytoplankton from a Perennially Ice-Covered Antarctic Lake: Acclimation to an Extreme Shade Environment

Phytoplankton in perennially ice-covered Lake Bonney (Antarctica)are exposed to a limited range of light variation both in termsof intensity (<1–3% of incident) and spectral distribution(blue-green) during the austral spring and summer. This relativeconstancy is due to continuous sunlight, optical filtering throughthe 4.2 m ice cap and an absence of vertical mixing. The effectsof this unique light environment on the structure and functionof the photosynthetic apparatus were studied using measurementsof P₇₀₀ reaction center content and spectral variation in photosystemII (PSII) fluorescence kinetics. Light-induced absorbance changeat both 700 nm and 810 nm was used to measure P₇₀₀ concentration.The average ratio of total Chl/P₇₀₀ was 743 (mol mol^–1),with a range of 480 to 1,039. These ratios were low in comparisonto previous studies of phytoplankton growing in low-light culturesor algae growing beneath Arctic sea ice. A sample from the deep(17 m) layer dominated by Chlamydomonas subcaudata was grownin enriched culture media. PSII fluorescence kinetics were measuredon thylakoid preparations in the presence of DCMU under blue-green(481 nm) and red (660 nm) light. C. subcaudata utilized blue-greenlight for photosynthesis more efficiently than the photobiologicallywell characterized C. reinhardtii (strain CC-124). These results,together with pigment analyses, suggest that carotenoids inLake Bonney phytoplankton are more important in light harvestingas opposed to photoprotection. (Received March 23, 1994; Accepted December 5, 1994)     

A probable lack of function of c-type cytochrome in the photosynthetic system of the blue-green alga Anabaena variabilis

Quantitative study of the cytochrome c acting in the photosyntheticsystem of the blue-green alga Anabaena variabilis (M-2) wasdone with membrane fragments and intact cells. Membrane fragments highly active in the NADP⁺-Hill reaction(above 200 µmoles/mg chl.a;-hr) retained photoresponsivecytochrome c equal only one-tenth that of P700, while the plastocyanincontent was almost equal to that of P700. The cytochrome contentin intact cells was a little larger than that in membrane fragmentson the chlorophyll a basis. However, the values relative toP700 (1/9) and plastocyanin (1/10) were identical with thosein membrane fragments. The content was also far smaller thanthat of reaction center II's (1/6). If the cytochrome mediatesall electrons from reaction center II, the cytochrome oxidation-reductionshould have a rate constant of 2.4?102 sec^–1 which isone order above of the rate constant of the cytochrome reduction(2.3 to 3.5?10¹sec^–1). These quantitative relationshipsindicate that in Anabaena variabilis (M-2), c-type cytochrome,either cytochrome f or algal cytochrome c, cannot function inthe main electron flow between two reaction centers. (Received September 8, 1978; )     

Heat-Stability of Iron-Sulfur Centers and P-700 in Photosystem I Reaction Center Complexes Isolated from the Thermophilic Cyanobacterium Synechococcus elongatus

Stabilities of iron-sulfur centers and reaction center chlorophyllP-700 in Photosystem I reaction center complex (CP1-a), isolatedby sodium dodecyl sulfate treatment from the thermophilic cyanobacteriumSynechococcus elongatus, were studied by EPR and optical spectroscopy.P-700 was destroyed by treatment at temperatures above 80?Cfor 5 minutes with a half inactivation temperature of 93?C.The three iron-sulfur centers F_A, F_B and F_X showed similar thermalstabilities and were half inactivated at about 70?C. Thus, theisolated Photosystem I reaction center complexes of S. elongatusare still highly resistant to heat. (Received May 9, 1990; Accepted June 25, 1990)     

Chromatographic separation of photosystems I and II from the thylakoid membrane isolated from a thermophilic blue-green alga

The thylakoid membrane of a thermophilic blue-green alga, Synechococcussp., was separated into four chlorophyll-containing fractionsby a single chromatographic manipulation with a diethylaminoethyl-cellulosecolumn after digitonin treatment. Photosystems I and II, orchlorophyll a forms, were unevenly distributed among the fourfractions, which were designated F-1, F-2, F-3 and F-4 in theorder of elution from the column. F-1 has a simple composition of the chlorophyll a form and totallylacks photochemical activity. This fraction may be an antennachlorophyll a-protein in the blue-green alga. F-2 is rich inshorter wavelength chlorophyll a forms and shows the three-bandedfluorescence emission spectrum characteristic of photosystemII at liquid nitrogen temperature. This fraction is highly activein 2,6-dichloroindophenol photoreduction and contains one photooxidizablecytochrome b₅₅₉ per 50–100 chlorophyll a, whereas theP-700 content is as low as one P-700 per 2,000 chlorophyll a.Thus, F-2 represents photosystem II in a highly purified state.F-3 is rich in photosystem I, since this fraction is inactivein 2,6-dichloroindophenol photoreduction, and contains one P-700per 200 chlorophyll a and smaller amounts of cytochrome b₅₅₉.Longer wavelength chlorophyll a forms are abundant and a peakat 730 nm is the most prominent in the low-temperature fluorescencespectrum in this fraction. F-4, which consists of larger membranefragments shows spectral and photochemical features similarto those of F-3. (Received August 8, 1979; )     

Chromatic Regulation of Photosystem Composition in the Photosynthetic System of Red and Blue-Green Algae

A chromatic adaptation in the photosynthetic quantum yield forthe light mainly absorbed by chlorophyll a (Chl a light) firstfound by Yocum (1951) was studied with one red and three blue-greenalgal strains. When the cells were grown under a weak Chl alight, the quantum yield in all the strains increased. Comparisonof photosystem (PS) compositions, including phycobilin (PBP)and Chl a antennae, reaction centers I and II, in the cellsgrown under the light mainly absorbed by PBP and Chl a revealedthat changes in quantum yield could be attributed to changesin the ratio of PS I/II; PS I/II becomes larger than 1 underPBP light but decreases to 1 in most cases under Chl a light.The change in the PS I/II ratio is due solely to the changesin the PS I population in the cell; PS II remains constant.These results are similar to the intensity-dependent responsein PS composition. A common hypothesis for both the chromatic and intensity-inducedregulation of PS composition was proposed based on the ideaof balance between the electron flow from H₂O to NADP drivenby PS I and II and the cyclic one driven by PS I. (Received May 16, 1985; Accepted September 4, 1985)     

The C550 photoresponse at room temperature observed in membrane fragments of the blue-green alga Anabaena variabilis

The C550 photoresponse at room temperature was studied withmembrane fragments of the blue-green alga Anabaena variabilis.The kinetics, light minus dark difference spectrum and DCMUeffect were the same as those reported for spinach chloroplasts.The photoresponse size suggested that the number of the photosystemII center is half that for the photosystem I center in thisorganism grown under our autotrophic culture conditions. (Received September 16, 1975; )     

Oscillatory kinetics of the number of photosynthetic system II centers in S2 and S3 states after flashes under various conditions

The kinetics of dark deactivation of centers in S₂ and S₃ stateswere studied in Chlorella pyrenoidosa in the presence of orthophenanthrolineand methylamine and at different temperatures under normal conditions.These kinetics of S₂ and S₃ evolution were no more monotonouswith dark time and showed oscillations even during the stabilityperiod of about 500 msec which is observed under normal conditions.Experimental analysis of these oscillations showed that someof the S₂ (or S₃) temporarily takes an inactive form withoutconversion to S₁ (or S₂), and some time later other inactivecenters are transformed into the active S₂ (or S₃ state. These oscillating kinetics explain the observed modificationsin the O₂-flash sequences as a function of the time intervalbetween flashes. The regulation mechanism which under normal conditions stabilizesthe number of active centers between 100 and 500 msec afterthe flashes seems to be disturbed: oscillations appear becausethe compensation between deactivation and the formation of anactive state from the temporary inactive form is not as completeas under normal conditions. (Received April 11, 1978; )     

Toxicity of Selenium to the Blue-green Algae, Anacystis nidulans and Anabaena variabilis

Selenate, selenite, selenomethionine, and selenopurine are toxicto Anacystis nidulans and Anabaena variabilis. These compoundsare less toxic in culture medium containing sulphate than insulphur-free medium, thus suggesting a protective role of sulphuragainst selenium toxicity Selenite is more toxic in agar plate cultures and less toxicin liquid cultures than selenate. Cells grown in the highestgrowth-permitting concentration of selenite in liquid mediumform a variable number of red granules No such granulation occursin cells treated with other seleno-compounds, indicating therebythat the mode of selenite action in blue-green algae differsfrom that of other selenium compounds     

The occurrence of the hydrogenase in some blue-green algae

Several blue-green algae were surveyed for the occurrence of the hydrogenase which was assayed by the oxyhydrogen or Knallgas reaction in the intact organisms. In aerobically grown cultures, the reaction was detectable in Anabaena cylindrica, Nostoc muscorum and in two Anabaena variabilis species, whereas virtually no activity was observed in Anacystis nidulans and Cyanophora paradoxa. In these latter two algae, the reaction was, however, found after growth under molecular hydrogen for several days, which drastically increased the activity levels with all the algae tested. In the nitrogen fixing species, the activity of the Knallgas reaction was enhanced when all combined nitrogen was omitted from the media. H₂ and hydrogenase could not significantly support the CO₂-fixation in photoreduction experiments with all blue-green algae investigated here. Hydrogenase was assayed by the dithionite and methyl viologen dependent evolution of hydrogen and was found to be present with essentially the same specific activity levels in preparations of both heterocysts and vegetative cells from Anabaena cylindrica. Na₂S₂O₄ as well as H₂ supported the C₂H₂-reduction of the isolated heterocysts. The H₂-dependent C₂H₂-reduction did not require the presence of oxygen but was strictly light-dependent where H₂ served as an electron donor to photosystem I of these cells. It is concluded that hydrogen can be utilized by two different pathways in blue-green algae.Abbreviations Chl chlrophyll - CP creatine phosphate - CP kinase creatine phosphokinase - DCMU N-(3,4-dichlorophenyl)N,N-dimethylurea     

Cyanidium caldarium as a bridge alga between Cyanophyceae and Rhodophyceae: Evidence from immunodiffusion studies

The primer-independent phosphorylase isozyme, a₂, of Cyanidiumcaldarium was used for immunization of rabbits. The immune serumwas tested against pure a₂ isozymes from blue-green, red, andgreen algae. Double immunodiffusion in agar indicated that therewas structural similarity in the isozyme from Cyanidium caldarium,the blue-green algae, Oscillaloria princeps, Pleclonema nostocorumand the red alga, Rhodymenia pertusa. Complete fusion of theprecipitin lines was obtained with these algae. However, onlypartial fusion was observed with the a₂ isozymes from Chlorophyceaesuch as Chlorella pyrenoidosa and Spirogyra setiformis. Spurformation on the precipitin lines occurred when the isozymesfrom these algae were tested against the immuneserum. The results were interpreted as indicative of the possible transitionstatus of Cyanidium caldarium between prokaryotic blue-greenalgae and eukaryotic red algae. It would appear that the Chlorophyceaeevolved along different lines from Cyanophyceae than did theRhodophyceae. (Received November 25, 1975; )     

Resistance to blue-green algal toxins by Bosmina longirostris

Bosmina longirostris was resistant to strains of Microcysrtsaeruginosa and Anabaena flosaquae previously reported to havelethal toxic effects on cladocerans. These blue-green algaewere of poor nutritional value to B.longirostris; survivorshipwas increased when fed these algae but reproduction was negligible.Results of feeding selectivity experiments showed that B.longirostrisdid not avoid consuming these blue-green algae, indicating thatthe mechanism for resistance must be post-ingestion. These resultssuggest that, unlike the other cladocerans tested, B.longirostriscould potentially coexist with toxic blue-green algal blooms.     

Effect of carbon dioxide concentration on pigmentation in the blue-green alga Anacystis nidulans

The pigment content in the blue-green alga Anacystis nidulanswas found to be dependent upon CO₂ concentration during growth.In cells grown with 1% CO₂ in air the total pigment constituted20.5% of the dry weight while it was only 11.1% of dry weightof cells grown in air (0.03% CO₂). This decrease in total pigmentwas found to be almost entirely ascribable to decrease in phycocyanin.Since light absorbed by phycocyanin has been shown to providenearly equal rates of photoreactions I and II, the "CO₂ control"of phycocyanin is viewed as an effective means of regulationof the photoreactions without upsetting the balance of operationof the two photoreactions. (Received December 25, 1970; )     

Contents of Cytochromes, Quinones and Reaction Centers of Photosystems I and II in a Cyanobacterium Synechococcus sp.

The contents of photosystem I and photosystem II reaction centers,cytochrome c-553, cytochrome c-550, cytochrome f, cytochromeb-559, cytochrome b-563, plastoquinone and vitamin K₁ in thecyanobacterium Synechococcus sp. were determined. About threephotosystem I reaction centers were present for each photosystemII reaction center. The amounts of cytochromes functioning betweenthe two photosystems were approximately half those of the photosystemI reaction center. Plastocyanin was not detected, while plastoquinoneand vitamin K₁ were present in excess of other electron carriersand reaction centers. The results indicate the importance ofplastoquinone and cytochrome c-553 for cooperation of the tworeaction centers through electron transport. ¹Present address: Toray Basic Research Laboratory, 1111 Tebiro,Kamakura, Kanagawa 248, Japan. (Received June 17, 1982; Accepted January 17, 1983)     

Reversible Inhibition of the Photosynthetic Water-Splitting Enzyme System by SO2-Fumigation Assayed by Chlorophyll Fluorescence and EPR Signal in Vivo

The effect of SO₂ fumigation (2 ppm, v/v) on photosynthesisin spinach leaves in vivo was investigated by measuring Chla fluorescence (OIDP transient) and the electron paramagneticresonance (EPR) signal I. SO₂ fumigation raised the I levelto yield the ID dip and suppressed the DP transient before anyvisible damage occurred in the leaf. In SO₂-fumigated leaves,the time course of EPR signal I indicates that reduction ofP700 by white light illumination was inhibited but dark reductionof P700 was not significantly affected. Photosynthetic O₂ evolutionwas also inhibited by SO₂ fumigation. All of these effects werereversible after removal of SO₂. The variable part of the fluorescencein the presence of DCMU was only slightly affected and decreasedas the fumigation time increased. We concluded that SO₂ fumigationreversibly inhibits the photosynthetic water-splitting enzymesystem and it injures the reaction center of PS II in vivo whenthe fumigation time is prolonged. We discussed the role of possible toxicants derived from SO₂within the leaf on the basis of the SO₂ action on Chl a fluorescence. (Received December 8, 1983; Accepted May 7, 1984)