Spectrophotometric measurement of plastoquinone photoreduction in the blue-green alga,Phormidium uncinatum

The redox state of plastoquinone was measured in vivo in the blue-green alga, Phormidium uncinatum by means of a double beam UV-spectrophotometer. The difference in absorbance of the oxidized and the reduced forms of plastoquinone was amplified, and stored and averaged in a computer. The redox state was changed by two alternating actinic light beams. When one actinic wavelength was kept constant at 700 nm (PSI) variation of the other yielded an action spectrum representing photosystem II. The inhibitors of the photosynthetic electron transport chain, DCMU and DBMIB, reduced the difference in absorbance between the oxidized and reduced forms of plastoquinone.Abbreviations DBMIB 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone - DCMU 3-(3,4-dichlorophenyl)-1, 1-dimethylurea     

The hydrogenase-nitrogenase relationship in the blue-green algaAnabaena cylindrica

Nitrogen-fixingAnabaena cylindrica cells are found to evolve hydrogen in high quantities in the presence of CO plus C₂H₂. Studies with the inhibitors dichlorophenyldimethylurea (DCMU), disalicylidenepropanediamine (DSPD), dibromothymoquinone (DBMIB), undecylbenzimidazole (UDB) and chloro-carbonyl-cyanide-phenylhydrazone (CCCP) and also withAnabaena grown on nitrate- and ammonia-nitrogen show that the H₂-formation is due to the ATP-dependent H₃O⁺-reduction catalysed by nitrogenase. In control experiments CO plus C₂H₂ inhibited the activities of a cell-free hydrogenase fromClostridium pasteurianum. It is concluded that Anabaena has a hydrogenase whose natural function is to recycle the H₂ lost by the action of nitrogenase.Abbreviations Cl-CCP m-chloro-carbonyl-cyanide-phenylhydrazone - DSPD disalicylidenepropanediamine(1–3) - DBMIB dibromothymoquinone - DCMU N-(3,4-dichlorophenyl) NN-dimethyl-urea - UDB 2-undecyl-benzimidazole     

Physiology of sulfide tolerance in a thermophilic Oscillatoria

Oscillatoria amphigranulata is a fast-growing (3 doublings/day) cyanobacterium isolated from sulfide hot springs in New Zealand. Photosynthesis, as measured by incorporation of [¹⁴C]-HCO ₃ ^- , was initially inhibited by 0.3–1.5 mM sulfide at pH 7.9–8.1. However, conversion to sulfide-dependent anoxygenic photosynthesis occurred in about 2 h or less under light intensities of 3–14 klx. Under the stimulation of higher light intensity (8–14 klx) a partial recovery of oxygenic photosynthesis also occurred. It was concluded that oxygenic photosynthesis was responsible for 21–42% of the total incorporation at sulfide concentrations of 1.0–0.3 mM, respectively. This contribution was suppressed at 1.5 mM sulfide and not elicited under lower light intensities (3–7 klx). As judged by the inhibitory effect of 10 g/ml chloramphenicol protein synthesis was required for attainment of both anoxygenic photosynthesis and photosystem II recovery. Sulfide could not be replaced by thiosulfate, elemental sulfur or dithionite as electron donors in photosynthesis, but elemental sulfur could serve as the sole assimilatory source of sulfur. Oxygenic photosynthesis was inhibited by DCMU [3-(3,4-dichlorophenyl)-1,1-dimethylurea] or DBMIB (2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone), but sulfide relieved the effect of either inhibitor in adapted cells, indicating that electrons derived from sulfide enter the photosynthetic electron transport chain at a point beyond plastoquinone.Uncommon abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DBMIB 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone - DSPD disalicyclidene propanediamine - DNP-INT 2-4-dinitrophenyl ether of 2-iodo-4-nitrothymol - TMPD N,N,N,N-tetramethyl-p-phenylenediamine - PPO 2,5-diphenyloxazole - POPOP 1,4-bis-2-(5-phenyl oxzolyl) benzene     

Observations on the photohydrogen producing activity during the synchronous cell cycle of Scenedesmus obliquus

In anaerobically adapted samples of synchronized cultures of the unicellular green alga Scenedesmus obliquus it was observed that both the rate and the maximum volume of hydrogen produced in the light changed in a parallel fashion over the life cycle. These two parameters of cells of the 16th h were 3 times greater than the comparable values for cells of the 8th h. Although both photosystems are involved in photohydrogen production the patterns seen over a complete life cycle (24 h) for hydrogen metabolism was inverse to that noted for changes in the photosynthetic capacity. The provision of either glucose, ethanol or acetate to 8th and 16th h cultures enhanced photohydrogen production of the 8th to the same level as the 16th h. From these findings, and also from the observation that the starch content is low at the 8th but 4 fold at the 16th h, it is apparent that in autotrophic cultures an endogenous organic compound, and not water, serves as the electron donor for photohydrogen production. Since free glucose was not detected the natural substrate is most likely starch. From experiments with monochromatic light and observations on the inhibitory action of DCMU and DBMIB on photohydrogen production we conclude that the major portion of the machinery for photohydrogen production in Scenedesmus requires both PS I and PS II participation and the input of electrons from the natural substrate proceeds through PS II.The alternate possibility that glucose, acetate and ethanol also act as inhibitors of reactions, most probably photophosphorylation, which compete with photohydrogen production was suggested by some experiments. The subsequent modulation of hydrogenase activity was discussed as a possible reason for the enhancement of photohydrogen production.Abbreviations CCCP carbonylcyanide-m-chlorophenylhydrazone - Chl chlorophyll - DCMU 3-(3, 4-dichlorophenyl)-1,1-dimethyl-urea - DBMIB 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone - NAD nicotinamide adenine dinucleotide - PSI photosystem I - PSII photosystem II - PCV packed cell volume     

Investigations on the phototactic orientation of Anabaena variabilis

Phototaxis of the blue-green alga Anabaena variabilis was studied using both population method and observation of single trichomes by microscope. The trichomes react positively at low and negatively at high illuminance. The inversion point lies at about 1000 1x. The action spectrum of positive phototaxis indicates that the photosynthetic pigments chlorophyll a, C-phycocyanin and allo-phycocyanin are involved in the absorption of the active light. The same range of wavelengths is active in negative phototaxis, but in addition, wavelengths between 500 and 560 nm and between 700 and 750 nm are also effective. Obviously pigments of unknown chemical nature are sharing in light absorption. Two alternatives are discussed. Since inhibitors of photosynthesis such as DCMU and DBMIB do not affect phototactic orientation, a direct coupling of phototaxis with photosynthesis can be excluded.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DBMIB Dibromothymoquinone (2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone) Presented in part at the International Symposium on Photosynthetic Prokaryotes: August 22–28, 1976, Dundee, Scotland     

Photomovement in Cyanophora paradoxa

Photomovement has been studied in the symbiontic association of the colorless flagellate, Cyanophora paradoxa Korschikoff with the cyanelles, Cyanocyta korschikoffiana. There is no phototactic orientation in this organism, but a photokinetic effect. In addition, the cells show a pronounced step-up photophobic response (however no or only a weak step-down response). The phobic response is mediated by a subset of the photosynthetic pigments located in the symbiontic cyanelles. It is linked to the noncyclic photosynthetic electron transport chain but it is independent of the photosynthetic generation of a proton gradient and the ATP synthesis linked to it.Abbreviations CCCP carbonyl cyanide m-chlorophenyl hydrazone - DBMIB 2,5-dibromo-3-methyl-6-isopropylbenzo quinone - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea     

The significance of hydrogenase activity for the energy metabolism of green algae: anaerobiosis favours ATP synthesis in cells of Chlorella with active hydrogenase

In cells of the green alga Chlorella fusca, which contain active hydrogenase(s), the concentration of ATP, NADH and NADPH were measured during a 5 h period of anaerobiosis in the dark and upon subsequent illumination with high light intensities (770 W/m²), conditions which favour optimal hydrogen photoproduction.ATP concentrations were also determined in cells of Chlorella fusca, whose hydrogenase was inactivated prior to illumination, and in cells of Chlorella vulgaris which do not contain hydrogenase. In the dark, the ATP concentration increased slightly during anaerobiosis in cells with active hydrogenase. This increase in ATP concentration was accompanied by an increase of NADH and a decrease of NADPH content.Upon illumination, the ATP content increased in cells with an active hydrogenase, whereas the NADH content decreased. The rate of phosphorylation was twice that observed in cells without active hydrogenase.This ATP synthesis in the light was not inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) (10 mol/l) nor by carbonylcyanide-3-chlorophenyl-hydrazone (CCCP) (1 mol/l) but was diminished by 500 mol/l dibromothymoquinone (DBMIB) and 6 mol/l carbonylcyanide-3-chlorophenyl-hydrazone (CCCP).It was concluded that an active hydrogenase can support ATP production under anaerobic conditions in the dark as well as in the light. NADH might serve in vivo as electron donor for a fermentative production of hydrogen in the light.Possible mechanisms underlying ATP production under anaerobiosis and hydrogen productive conditions are discussed.Abbreviations CCCP Carbonylcyanide-3-chlorophenyl-hydrazone - DBMIB dibromothymoquinone - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - FCCP carbonylcyanide-p-trifluormethoxyphenyl-hydrazone - HEPES N-2-hydroxyethylpiperazin-N-2-ethan-sulfonic acid - PSI II, photosystem I, II respectively - PQ plastoquinone     

Photoinhibition in Chlamydomonas reinhardtii: Effect on state transition,intersystem energy distribution and Photosystem I cyclic electron flow

The energy distribution, state transitions and photosynthetic electron flow during photoinhibition of Chlamydomonas reinhardtii cells have been studied in vivo using photoacoustics and modulated fluorescence techniques. In cells exposed to 2500 W/m² light at 21 °C for 90 min, 90% of the oxygen evolution activity was lost while photochemical energy storage as expressed by the parameter photochemical loss (P.L.) at 710–720 nm was not impaired. The energy storage vs. modulation frequency profile indicated an endothermic step with a rate constant of 2.1 ms. The extent of the P.L. was not affected by DCMU but was greatly reduced by DBMIB. The regulatory mechanism of the state 1 to state 2 transition process was inactivated and the apparent light absorption cross section of photosystem II increased during the first 20 min of photoinhibition followed by a significant decrease relative to that of photosystem I. These results are consistent with the inactivation of the LHC II kinase and the presence of an active cyclic electron flow around photosystem I in photoinhibited cells.Abbreviations PS I, PS II Photosystem I and Photosystem II respectively - P.L. photochemical loss - DCMU 3-(3,4-dichlorophenyl-1,1-dimethyl urea - LHC II light harvesting chlorophyll a,b-protein complex of PS II - DBMIB 2,5 dibromo-3-methyl-6-isopropyl-p-benzoquinone     

Studies on the pathway of cyclic electron flow in mesophyll chloroplasts of a C4 plant

1. Cyclic photophosphorylation driven by white light, as followed by ¹⁴CO₂ fixation by mesophyll chloroplast preparations of the C₄ plant Digitaria sanguinalis, was specifically inhibited by disalicylidenepropanediamine (DSPD), antimycin A, 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIb), 1-ethyl-3(3-dimethylaminopropyl)-carbodiimide (EDAC), and KCN suggesting that ferredoxin, cytochrome b₅₆₃, plastoquinone, cytochrome f, and plastocyanin are obligatory intermediates of cyclic electron flow. It was found that 0.2 μM DCMU and 40 μM o-phenanthroline blocked noncyclic electron flow, stimulated cyclic photophosphorylation, and caused a partial reversal (40–100%) of the inhibition by DBMIB and antimycin A, but not DSPD.

2. Cyclic photophosphorylation could also be activated using only far-red illumination. Under this condition, however, cyclic photophosphorylation was much less sensitive to the inhibitors DBMIB, EDAC and antimycin A, but remained completely sensitive to DSPD and KCN. Inhibition in far-red light was not increased by preincubating the chloroplasts with the various inhibitors for several minutes in white light.

3. The striking correspondence between the effects of photosystem II inhibitors, DCMU and o-phenanthroline, on cyclic photophosphorylation under white light and cyclic photophosphorylation under far-red light (in the absence of photosystem II inhibitors) suggests that electrons flowing from photosystem II may regulate the pathway of cyclic electron flow.     

Über die energetische Kopplung der Nitritassimilation von Grünalgen an Atmung und Photosynthese

Summary Inhibitors and uncouplers of phosphorylation, i.e., arsenate, 2.4-dinitrophenol (DNP), pentachlorophenol (PCP), and carbonyl cyanide m-chlorophenylhydrazone (CCCP), inhibit the assimilation of nitrite by the green alga Ankistrodesmus braunii in the dark and in the light. In a medium containing nitrate, these inhibitors interrupt nitrate reduction at the level of nitrite. In phosphatedeficient algae, the assimilation of nitrite can be decreased by a concomitant, energy-dependent uptake of chloride and phosphate ions. These results support the assumption that high-energy phosphate is required for the assimilation of nitrite.CO₂ and glucose (after pre-illumination) increase nitrite assimilation in the light. Photosynthetic nitrite reduction is inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU), an inhibitor of oxygen evolution, and by disalicylidene-propanediamine-(1,3) (DSPD), an inhibitor of the photosynthetic reduction of ferredoxin.

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Abkürzungen CCCP Carbonylcyanid-m-chlorphenylhydrazon - DCMU 3-(3,4-Dichlorphenyl)-1,1-dimethylharnstoff - DNP 2,4-Dinitrophenol - DSPD Disalicylidenpropandiamin-(1,3) - PCP Pentachlorphenol - JAA Jodacetamid     

The cyclic electron pathways around photosystem I in Chlamydomonas reinhardtii as determined in vivo by photoacoustic measurements of energy storage

The photoacoustic technique was used to measure energy storage by cyclic electron transfer around photosystem I in intact Chlamydomonas reinhardtii cells illuminated with far-red light (>715 nm). The in-vivo cyclic pathway was characterized by investigating the effects of various chemicals on energy storage. Participation of plastoquinone and ferredoxin in the cyclic electron flow was confirmed by the complete suppression of energy storage in the presence of the plastoquinol antagonist 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB) and the ferredoxin inhibitors/competitors methylviologen, phenylmercuric acetate and p-benzoquinone. Two alternative electron cycles are demonstrated to operate in vivo. One cycle is sensitive to antimycin A, myxothiazol and 2-(n-heptyl)-4-hydroxyquinoline N-oxide (HQNO) and is catalyzed by ferredoxin which reduces plastoquinone through a route involving cytochrome b ₆ and its protonmotive Q-cycle. The other cycle is unaffected by the above-mentioned inhibitors but is sensitive to N-ethylmaleimide (NEM), an inhibitor of the ferredoxin-NADP reductase, and 2-monophosphoadenosine-5-diphosphoribose (PADR), an analogue of NADP, showing that the electron recycling was mediated by NADPH. Possibly, electrons enter the plastoquinone pool through the action of a NAD(P)H dehydrogenase, which is insensitive to classical inhibitors of the mitochondrial NADH dehydrogenase. Loss of energy storage by photosystem-I-driven cyclic electron transfer in farred light was observed only when antimycin A, myxothiazol or HQNO was used in combination with NEM or PADR. Analysis of the light-intensity dependence and the rate of in-vivo cyclic electron transfer in the presence of various inhibitors indicates that the NADPH-dependent electron-cycle is the preferential cyclic pathway in Chlamydomonas cells illuminated with far-red light.Abbreviations A^max maximal photothermal signal - Cyt cytochrome - DBMIB 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone - DCMU (diuron) 3-(3,4-dichlorophenyl)-1,1-dimethylurea - ES photochemical energy storage - FNR ferredoxin NADP⁺ reductase - HQNO 2-(n-heptyl)-4-hydroxyquinoline N-oxide - NEM N-ethylmaleimide - P₇₀₀ reaction-center pigment of PSI - PADR 2-monophosphoadenosine-5-diphosphoribose - pBQ p-benzoquinone - PMA phenylmercuric acetate We are very grateful to Dr. M.-H. Montane (Cadarache, Saint-Paul-lez-Durance, France) for her advice in the electroporation experiments.     

NADH as electron donor for the photosynthetic membrane of Chlamydomonas reinhardii

A chloroplast fraction from Chlamydomonas reinhardii cells can oxidize NADH in the light, unlike chloroplasts of higher plants. The Chlamydomonas preparation catalyzes electron flow from NADH to methylviologen or ferredoxin to evolve hydrogen (in the presence of a hydrogenase) or take up oxygen. The NADH photooxidation is sensitive to rotenone, dibromothymoquinone and dicyclohexylcarbodiimide. This suggests that a rotenone sensitive NADH dehydrogenase is coupled on the plastoquinone reduction site of the potosynthetic electron flow system. On sonication of the particles NADH photooxidation is lost but may be restored by a protein fraction from an acetone extract plus plastocyanin.Abbreviations DAD diaminodurene - DCCD dicyclohexylcarbodiimide - DCMU (3,3-dichlorphenyl)-N·N dimethyl urea - DBMIB dibromothymoquinone - DNP-INT dinitro-phenylether of 2-iodo-4-nitrothymol - MV methylviologen - chl chlorophyll Dedicated to Professor Dr. O. Kandler on the occasion of his 60th birthday     

Sulphate uptake in the unicellular marine red algaRhodella maculata

Sulphate uptake by the unicellular marine red algaRhodella maculata conforms to Michaelis-Menten kinetics. Two uptake systems have been found: a low affinity system with an apparentK _m of 22 mM, and a high affinity system with an apparentK _m of 63.4 M. Transition from the low to the high affinity system can occur within 2.5 min, in response to a decrease in the ambient sulphate concentration to below 10 mM. Assimilation rates in the dark are about 20% those in the light, although enhancement by light is independent of the quanlity of light supplied above 27 mol m^-2 s^-1. Use of metabolic inhibitors indicates that photophosphorylation provides the main source of energy for sulphate assimilation, through both cyclic and non-cyclic electron flow.Abbreviations used APS-kinase ATP:adenylyl-sulphate 3-phosphotransferase (E.C. 2.7.1.25) - ATP-sulphurylase ATP:sulphate adenylyltransferase (E.C.2.7.74) - DCMU [3-(3,4-dichlorophenyl)]-1,1 dimethylurea - 2,4 DNP 2,4-dinitrophenol - DBMIB Dibromothymoquinone (2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone)     

Effects of 2,5-Dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB) on Light Induced and Glycolytic Phosphate Uptake in Scenedesmus

The effects of DBMIB on photophosphorylation and glycolysis in Scenedesmus obtusiusculus Chod. were investigated by measuring the uptake of inorganic phosphate. To analyze the effects of DBMIB on the different energy coupling possibilities in open chain and cyclic photophosphorylation, DBMIB was given to the algae in narrow concentration intervals between 10^?6M to 10^?4M, either alone, or in combination with DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea) or desaspidin. DBMIB inhibits non-cyclic as well as cyclic photophosphorylation in Scenedesmus. However, the DCMU resistant photophosphorylation reactions are less sensitive to DBMIB than the open chain photophosphorylating system in non-DCMU treated cells. Low concentrations of DBMIB even released a part of the DCMU inhibition. Experiments with combinations of DBMIB and desaspidin also indicated that cyclic photophosphorylation is less sensitive to DBMIB than non-cyclic. The inhibition of DCMU resistant cyclic phosphorylation by DBMIB, which is a competitive inhibitor of quinones, indicated a participation of plastoquinones in this type of energy coupling as well as in the non-cyclic and DCMU-sensitive processes. The cyclic and the non-cyclic photophosphorylation pathways probably use different parts of the plastoquinone pool. For the purpose of the experiments, it was necessary to produce data for the effect of DBMIB (10^?6–10^?4M) on glycolysis. The highest concentration gave 50% inhibition.     

Photosystem I cyclic electron transport: Measurement of ferredoxin-plastoquinone reductase activity

Absorbance changes of ferredoxin measured at 463 nm in isolated thylakoids were shown to arise from the activity of the enzyme ferredoxin-plastoquinone reductase (FQR) in cyclic electron transport. Under anaerobic conditions in the presence of DCMU and an appropriate concentration of reduced ferredoxin, a light-induced absorbance decrease due to further reduction of Fd was assigned to the oxidation of the other components in the cyclic pathway, primarily plastoquinone. When the light was turned off, Fd was reoxidised and this gave a direct quantitative measurement of the rate of cyclic electron transport due to the activity of FQR. This activity was sensitive to the classical inhibitor of cyclic electron transport, antimycin, and also to J820 and DBMIB. Antimycin had no effect on Fd reduction although this was inhibited by stigmatellin. This provides further evidence that there is a quinone reduction site outside the cytochrome bf complex. The effect of inhibitors of ferredoxin-NADP⁺ reductase and experiments involving the modification of ferredoxin suggest that there may be some role for the reductase as a component of FQR. Contrary to expectations, NADPH₂ inhibited FQR activity; ATP and ADP had no effect.Abbreviations AQS 9,10-anthraquinone-2-sulphonate - DBMIB 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethyl urea - dimaleimide N,N-p-phenylenedimaleimide - EDC N-(dimethylaminopropyl)-N-ethylcarbodiimide - Fd ferredoxin - FNR Fd-NADP⁺ oxidoreductase - FQR Fd-PQ reductase - GME glycine methyl ester - J820 tetrabromo-4-hydroxypyridine - PC plastocyanin - PMS N-methylphenazinium methyl sulphate - PS Photosystems I and II - PQ plastoquinone - Q quinone - Q_r and Q_o sites of quinone reduction and oxidation, respectively - sulpho-DSPD disulphodisalicylidenepropane-1,2-diamine     

Characterization of synchronized cultures of Bumilleriopsis filiformis

Activity of the photosynthetic apparatus of synchronized cultures was studied with the xanthophycean alga Bumilleriopsis filiformis, following the kinetics of fluorescence induction and photooxidation of cytochrome f (= cytochrome c-553) of intact cells. During the beginning of the cell-division phase, minimum cellular photosynthetic activity is observed and a maximum after its completion, which is accompanied by corresponding changes in Hill reaction activity and re-reduction of cytochrome f by photosystem II light. At minimum activity, the level of steady state fluorescence was higher than at the maximum. This is due, at least in part, to the diminished electron flow between the two photosystems seemingly caused by decreased photosystem I activity. This explanation was suported by the kinetics of cytochrome-f photooxidation.Thus, electron transport activity of both photosystems appears to vary during the cell cycle.Abbreviations pBQ p-benzoquinone - DBMIB 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DCIP dichlorophenolindophenol - MV methylviologen (paraquat) - Q fluorescence quencher (in photosystem II)     

Interaction of the photosynthetic and respiratory electron transport chains producing slow O2 signals under flashing light in Synechocystis sp. PCC 6803

We investigated the slow signal of apparent O₂ release under brief light flashes by using mutants of Synechocystis sp. PCC 6803 which lacked CP43 and D1. The slow signal was present at higher amplitudes in the mutants. It was inhibited by starving the mutants of glucose (>90%), by 10 mM NaN₃ (85%) and by boiling samples for 2 min (100%). In the mutants and in the wild-type, the slow signal was 95% inhibited by the combination of DBMIB (2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone) and HQNO (2-n-heptyl-4-hydroxyquinoline-N-oxide). In the wild type, the addition of DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea) or CCCP (carbonylcyanide m-chlorophenylhydrazone) completely inhibited photosynthetic O₂ evolution, yet failed to inhibit the slow signal. We explain the kinetics of the wild-type signal as a positive deflection due to the inhibition of respiration by PS I activity, and a negative deflection due to the stimulation of respiration by electrons originating from PS II. We found no evidence of a meta-stable S₃ in Synechocystis sp. PCC 6803 that could contribute to the slow signal of apparent O₂ release. We present a calculation which involves only averaging, division and subtraction, that can remove the contribution of the slow signal from the true photosynthetic O₂ signal and provide up to a 10-fold improved accuracy of the S-state models.Abbreviations ADRY Acceleration of the Deactivation Reactions of the water-splitting enzyme system Y - Ant-2-p 2-(3-chloro-4-trifluoromethyl)-anilino-3,5-dinitrothiophene - CCCP carbonylcyanide m-chlorophenylhydrazone - DBMIB 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone, a.k.a. Dibromothymoquinone - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) - HQNO 2-n-heptyl-4-hydroxyquinoline-N-oxide - S. 6803 Synechocystis sp. PCC 6803     

Isolation of mutants of the cyanobacterium,Anabaena variabilis,impaired in photoautotrophy

Mutants ofAnabaena variabilis Kütz. that have a decreased ability to grow photoautotrophically have been isolated by a modification of the techniques used to isolate auxotrophic mutants of that filamentous cyanobacterium, and have been stably propagated. Three mutants have a reduced content of phycocyanin and, as determined by in situ assays of partial reaction sequences of photosynthesis, an impairment in photosystem II. Three other strains, all of which appear to have a normal complement of carotenoids when grown heterotrophically, are sensitive to light.Abbreviations Used TES N-tris(hydroxymethyl)-methyl-2-aminoethanesulfonic acid, sodium salt - HEPES N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid, sodium salt - MV methylviologen - DBMIB 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone - DAB 3,3-diaminobenzidine - P-BQ p-benzoquinone - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - Fecy K-ferricyanide - NTG N-methyl-N-nitro-N-nitrosoguanidine     

Photomovement of the red alga Porphyridium cruentum (Ag.) Naegeli

Photophobic reactions of the red alga Porphyridium cruentum have been studied by single cell observations and by population experiments with the light trap method. In white light traps photoaccumulation is saturated at about 6000 lx. Experiments with monochromatic light demonstrate the necessity of carefully separating the three basic light reactions, viz. phototaxis, photokinesis and photophobic response by an appropriate experimental set-up: In single-beam experiments trap wavelengths >695 nm cause photodispersal which is not due to photophobic entrance reactions, but is exclusively due to the positive photokinetic effect of the trap light. This photodispersal can be cancelled by a photokinetically active background light. In the short wavelength range not only photokinesis, but also phototaxis interferes with photophobic reactions thus affecting the density of photoaccumulations in the light trap. Phototactic and photokinetic interference can be avoided by a blue background light. The action spectrum measured this way indicates activity of photosystem I and photosystem II pigments in the perception of the step-down photophobic stimulus. Varying the wavelength of the background light at constant trap light absorbed mainly by photosystem I or photosystem II respectively, efficient spill-over of light energy from photosystem II to the light reaction of photosystem I could be demonstrated. From the results it is concluded that phobic reactions are induced by a decrease of the electron flow rate in the linear electron transport chain.