[Variability of light-induced circular dichroism spectra of photosystem I complexes of cyanobacteria].

Circular dichroism (CD) spectra of photosystem I (PSI) complexes of the cyanobacteria Thermosynechococcus elongatus, Arthrospira platensis and Synechocystis sp. PCC 6803 were studied. CD spectra of dark-adapted PSI trimers and monomers, measured at 77 K, show common bands at 669-670(+), 673(+), 680(-), 683-685(-), 696-697(-), 702(-) and 711(-) nm. The intensities of these bands are species specific. In addition, bands at 683-685(-) and 673(+) nm differ in intensity for trimeric and monomeric PSI complexes. CD difference spectra (P700(+)-P700) of PSI complexes at 283 K exhibit conservative bands at 701(-) and 691(+) nm due to changes in resonance interaction of chlorophylls in the reaction center upon oxidation of P700. Additional bands are observed at 671(-), 678(+), 685(-), 693(-) nm and in the region 720-725 nm those intensities correlate with intensities of analogous bands of antenna chlorophylls in dark-adapted CD spectra. It is suggested that the variability of CD difference spectra of PSI complexes is determined by changes in resonance interaction of reaction center chlorophylls with closely located antenna chlorophylls.

[Tetrapyrrole involvement in expression regulation of a nuclear gene of low-molecular-weight plastid protein ELIP].

An inhibitor analysis was used for studying the tetrapyrrole role in the regulation of the expression of the nuclear gene encoding a low-molecular-weight protein, a stress plastid light-inducible protein ELIP. 2,2'-Dipyridyl and norflurazon were used as inhibitors. Experiments with dipyridyl demonstrated that tetrapyrroles were involved in the regulation of Elip gene expression, inhibiting it by approximately 50%. Similar results were obtained when there was photodestruction of the chloroplasts, caused by a plant treatment with norflurazon. The results confirm the involvement of the chloroplasts in the regulation of the nuclear gene expression coding for plastid proteins. Tetrapyrroles are important contributors to this process.

[Dynamics of excitation in the photosystem I of cyanobacteria: transfer in the antenna, capture by the reaction site, and dissipation]. / Dinamika énergii vozbuzhdeniia v fotosisteme I tsianobakterii: perenos v antenne, zakhvat reaktsionnym tsentrom, dissipatsiia.

The structure of a complex of photosystem I (PSI) of cyanobacteria and the mechanisms of the functioning of the antenna and PSI reaction site were described. The complex of PSI in thylakoids of cyanobacteia is organized as a trimer whose antenna is enriched in long-wave chlorophylls. The energy absorbed by these chlorophyls migrates to P700, inducing its oxidation. Long-wave chlorophyls are also involved in the dissipation of excessive energy; both the cation radical of P700 and the triplet of P700 effectively quench the fluorescence of long-wave chlorophyll of PSI. The energy exchange between the antennas of monomers in the trimer of PSI stimulates the dissipation of electron excitation energy, protecting the complex against photodestruction. The kinetics of energy migration in the antenna and charge separation in the reaction site of PSI trimers was studied using subpicosecond spectroscopy. Long-wave chlorophylls of PSI do not substantially affect the energy migration in the heterogeneous antenna of PSI but slow down the capture of energy of P700. The separation of changes in the reaction site of PSI is the most rapid among the known reaction sites.

[A new type of adaptation of the cyanobacterium Spirulina platensis to illumination conditions]. / Novyi tip adaptatsii tsianobacterii Spirulina plantensis k usloviiam osveshcheniia.

Incubation of cells of the cyanobacterium Spirulina platensis under conditions of exposure to low-intensity (2-3 microE m-2 s-1) red light, which was predominantly absorbed by photosystem I (PS I), caused atypical adaptation changes. Invariable pigment composition and stoichiometry of photosystems was observed in the cells incubated under these conditions against the background of a decrease in the rate of photosynthetic fixation of CO2 (by one-half) and a 1.5-fold increase in the rate of dark respiration relative to cells incubated under conditions of exposure to green light. Comparison of these data with a high rate of dark relaxation of P700+ in the presence of diuron suggests that deficiency of reduced equivalents at the donor side of PS I in the Spirulina cells exposed to red light is compensated by electron supply from the respiratory chain NAD(P)H dehydrogenase complex.

[Interaction of the photosystem 1 reaction center with antenna chlorophyll in a pigment-protein complex isolated from pea chloroplasts]. / Vzaimodeistvie reaktsionnogo tsentra fotosistemy 1 s antennym khlorofillom v pigment-belkovom komplekse, vydelennom iz khloroplastov gorokha.

Using a specially developed phosporoscopic attachment to spectropolarimeter, light induced spectra of circular dichroism (CD) in region 600-750 nm were measured for a pigment protein complex of photosystem 1 (PC-1) isolated from pea chloroplast (chlorophyll : P700 = 40). Minor components at 672 and 678 nm are observed in light induced spectra besides the components of dimer splitting of P700 Qy transition at 691 and 698 nm. Haussian deconvolution of light induced CD spectra of P700 and low temperature CD spectrum of PC-1 indicates that minor components are due to forms of antenna chlorophylls Chl672 and Chl678, rotational strength of that is changed by 2-4% as a result of P700 oxidation. Long term incubation of PC-1 with Triton X-100 inhibits P700 and destroys longwave optically active chlorophyll forms. A strong relation between dichroic density of 693 nm band in CD spectrum of PC-1 and the value of light induced absorption change at 698 nm could be used to determine P700 concentration on the basis of CD spectrum of PC-1. Such a relation shows that Chl693 is an important component of photo-system 1 reaction center. It is suggested that P700 is not an isolated dimer but it is included in the local complex from 8-10 chlorophyll molecules (Chl672, Chl678, Chl686, Chl693).

[Effect of secondary structure on the rate dark reduction of P700+ with ascorbate of the photosystem I complex]. / Vliianie vtorichnoi struktury na skorost' temnovogo vosstanovleniia P700+ askorbatom kompleksa fotosistemy I.

Relationship was studied between the spectra of KD, absorption and fluorescence and kinetics of P700+ dark reduction with exogenous donor and sodium dodecyl concentration inducing a conformation transition of the protein globule. It has been shown that with a decrease of the detergent concentration from 0.01 to 0.06% an increase of the portion of the protein globule-helical regions (from 10 to 30%) and an essential decrease of the time of P700+ dark reduction with ascorbate take place. The changes of KD, absorption and fluorescence spectra of chlorophyll a observed in the same region of detergent concentration do not correlate with the changes of the secondary structure of the protein part of the pigment-protein complex. It is suggested that accelerated reduction of P700+ with ascorbate is conditioned by an increase of accessibility of exogenous donor to the reaction centre resulting from conformation changes of the complex protein part.

[Effects of pyridazinones and cerulenin on the biosynthesis and functional state of photosystem 2 in barley leaves]. / Vliianie piridazinonov i tserulenina na biosintez i funktsional'noe sostoianie fotosistemy 2 v list'iakh iachmenia.

The effects of pyridazinones and cerulenin on the formation of photosystem 2 in etiolated barley leaves and its functional state in green leaves were studied. It was shown that the reaction centers of photosystem 2 in greening leaves are formed after 2.5--3.0 hrs of illumination independently of herbicide treatment. In the leaves greening in the presence of pyridazinones and cerulenin and in green leaves treated by these substances a change in the chlorophyll state takes place, which is detected by a shortwave shift of the low temperature fluorescence maximum at 740 nm. Long-term treatment of greening and green leaves by pyridazinones increases variable fluorescence at 20 degrees. The inhibition of carotene synthesis by pyridazinones SAN 6706 and SAN 9789 during the greening is accompanied by a decrease of variable fluorescence at - 196 degrees and of its reversible part, as well as by an appearance of a light-induced dip of the fluorescence yield at 20 degrees slowly reversible in the dark. It is suggested that pyridazinones produce a 3-fold effect on the photosynthetic apparatus: 1) they block electron transport in the acceptor part of photosystem 2 and affect directly the reaction centers of this photosystem; 20 SAN 6706 and SAN 9789 inhibit carotene biosynthesis during greening of leaves, resulting in a formation of a photounstable pigment apparatus with a low amount of the reaction centers of photosystem 2; 3) pyridazinones which damage the membrane structure and probably the lipid composition of chloroplasts cause significant changes of the chlorophyll state; this effect is similar to that exerted by cerulenin.

[Effect of pyridazinone herbicides on the photosynthetic electron transport chain of chloroplasts and Chlorella]. / Deistvie piridazinovykh gerbitsidov na fotosinteticheskuiu tsep' perenosa élektrona khloroplastov i khlorelly.

In order to establish the site of pyridazinone herbicides action on the photosynthetic electron transport chain, their effect on the photochemical activity of chloroplasts and Chlorella was studied. It was shown that these compounds similar to diuron inhibit the delta F of chloroplasts but enhance the delta F and cause the disappearance of slow transient processes in Chlorella and change the light-off time course of delta F both in Chlorella and in the chloroplasts. The inhibiting effect is observed at herbicide concentration of 5 x 10(-6) M and is maximal at 10(-4) M. However, in contrast to diuron the herbicides enhance the msec afterglow in Chlorella cells; besides, even at concentration as high as 10(-4) M they only partly block photosynthetic oxygen evolution and the light-induced change of pH. Pyridazinone herbicides retard the delay of light-off delta F at-196 degrees C more efficiently than diuron. It is suggested that the herbicides under study inhibit the photosynthetic electron transport chain, however less efficiently than diuron; the inhibiting effect is decreased in the following order: SAN 9785, SAN 6706, SAN 9789. The herbicides affect mainly the acceptor part of the photosystem 2, retarding the electron transport from the intermediary acceptor to plastoquinone. In addition these herbicides may also have other sites of action in the region of photosystem 2.

[Spectral properties and structure of bacteriopheophytin a dimer]. / Spektral'nye svoistva i struktura dimera bakteriofeofitina a.

In alcohol-glycerol solutions of bacteriopheophytin alpha takes place dimer formation with a long wave absorption band at 857 nm, the dimerization constant enhances with glycerol content increasing in solution. The measurement of absorption, fluorescence and CD spectra allowed to characterize the main electronic transitions (Qy, Qx, Bxy) of the dimer. For the first electronic transition (Qy) of the dimer as compared to the monomer the same oscillator strength, spectral bands narrowing of splitting components and significant increase of rotation strength in CD spectrum were found. The structural model of bacteriopheophytin a dimer is suggested on the basis of the data obtained. Coincidence of the values of the long wave shift and exitonic splitting of Qy transition for the dimer investigated and antennae bacteriochlorophylls shows that the appearance of these properties does not require pigment protein interaction. Significant (20--30 times) exceeding of the rotation strength of Qy transition of the bacteriopheophytin dimer as compared ato the antennae complex pigments can indicate the absence of this dimer in intact structures.

[Dark and photo-induced changes in absorption and fluorescence spectra of phycobilisomes in the presence of dithionite]. / Temnovye i fotoindutsirovannye izmeneniia pogloshcheniia i fluorestsentsii fikobilisom v prisutstvii dintonita.

In order to test the possibility of photochemical participation of phycobilin pigments in photosynthesis, the ability of phycobilisomes for reversible photo-induced redox reactions was studied. The photo-induced fast reversible changes in the absorption and fluorescence spectra of phycobilisomes in the presence of dithionite were found. Simultaneously dithionite induced dark changes revealed by the decrease of the absorption and fluorescence yields. However, the dark and photo-induced changes differ in spectral parameters depending on dithionite concentration. The ability of phycobilisomes to photosensitive redox reactions was demonstrated. A possible nature of dark and photo-induced changes in the absorption and fluorescence spectra of phycobilisomes is discussed.

[Temperature independence of the rate of the rapid phase of P700+ dark reduction]. / Nezavisimost' ot temperatury skorosti bystroi fazy temnovogo vosstanovleniia P700+.

To elucidate the mechanism of interaction between P700+ and reduced primary electron acceptor in the reaction centres of photosystem I dark relaxation time course of absorption changes at 700 nm was studied at different temperatures. It is shown that in photosystem I subchloroplast fragments with partially inactivated endogenous secondary electron acceptors (treatment by ether or preliminary heating) the recombination of reduced primary acceptor and P700+ is found at -15 degrees C. In fragments with undamaged system of secondary acceptors the recovery of primary photoact in darkness is observed only at temperatures lower than -95 degrees C. At temperatures from -60 degrees to -170 degrees C the electron transfer from reduced primary acceptor to P700+ is described by the first order reaction with half time 250 ms; the rate of this process does not depend on the presence of secondary electron acceptor. The temperature independence of the rate of rapid phase P700+ dark reduction is interpreted as an indication of tunneling mechanisms from reduced primary acceptor to P700+.

[Effect of dehydration on functioning of photosystems of higher plants]. / Vliianie degidratatsii na funktsionirovanie fotosistem vysshikh rastenii.

The functional activity of both photosystems of higher plants and their thermoresistance in conditions of dehydratation of chloroplasts or subchloroplast fragments were studied. It is shown that dehydratation of the sample does not change the P700 amount capable to photooxidation. At 20 degrees in the time course of dark reduction of photooxidized P700 P(700+) in films two phases differing in rate were found. The relative contribution of each phase depends on the illumination duration. Since dehydratation blocks electron transfer between photosystems, the double phase dark reduction of P700+ in films reflects the electron flow from various components of potosystem 1 acceptor part. Dehydratation has little effect on properties of photosystem 1 acceptor part, because at low temperature the time courses of P700+ dark reduction in films and chloroplast or subchloroplast suspensions are similar. In contrast with potosystem 1, the functioning of photosystem 2, studied by light induced increase of fluorescence yield of chloroplasts, is blocked abruptly by water removal, but it could be partly restored by rehydratation of dried chloroplasts. The water removal increases the thermostability of both photosystems, however in suspension of the studied samples and also in their films photosystem 1 is more thermostable in comparison with photosystem 2.

[Photoinduced changes in adsorption at 800 nm related to photosystem I functioning]. / Fotoindutsirovannye izmeneniia pogloshcheniia pri 800 nm, sviazannye s funktsionirovaniem fotosistemy I.

The spectra and kinetics of light-induced absorbance changes in the near-infrared region of subchloroplast fragments enriched by P700 were studied. An increase in absorbancy within the region of 725--900 nm upon illumination was characterized by a maximum around 810 nm and by "shoulders" around 760 and 870 nm. Similar effects of thermal inactivation and low temperatures on the duration of dark recovery of light-induced absorbance changes at 700 nm and within the region of 725--900 nm suggest that the absorbance changes in the near-infrared region are due to photooxidation of P700. The values of P700 differential extinction coefficients at 810 nm are 8,2.10(3) M-1.cm-1 for digitonin fragments and 7,7.10(3) M-1.cm-1 for fragments prepared with the use of diethyl ester. It was shown that the value of midpoint oxidation-reduction potential measured for the absorbance changes at 810 nm (+492 mv) is higher than that measured at 700 nm (+475 mv).

[Nature of changes in the fluorescence process of P700-enriched chloroplast fragments]. / Pripoda izmenenii bykhoda fluorestsentsii fragmentov khloroplastov, obogashchennykh P700.

Spectral and photochemical properties of P700-enriched chloroplast fragments, obtained by ether treatment of liophylized digitonin fragments, were studied. It was shown that time course of fluorescence changes of isolated fragments (in contrast to digitonin fragments) at 20 degrees does not correspond to time course of absorption changes at 700 nm. Differences in low temperature fluorescence spectra of fragments, initially distinguished by redox states of photosystem 1 reaction centers were found. However, the fragments under study were incapable of light-induced changes of fluorescence yield at--196 degrees, independently of spectral region of measured fluorescence (lambda greater than 660 nm or lambda greater than 710 nm), though these fragments reveal phototransformation of P700. Thus changes in the low temperature fluorescence spectra cannot be accounted for by redox changes of P700. The fragments, isolated by ether treatment at 20 degrees as well at--196 degrees do not reveal light-induced fluorescence changes caused by redox changes of P700. The fluorescence changes observed may be due to accessory photoprocesses of chlorophyllprotein complex.

[Study of the acceptor portion of photosystem I according to the temperature relationships of P700 photoconversions]. / Issledovanie aktseptornoi chasti fotosistemy I po temperaturnoi zavisimosti fotoprevrashchenii P700.

The functioning of the acceptor part of photosystem I was studied by temperature dependence of time course of light induced absorbtion changes at 700 nm of digitonin chloroplast fragments, enriched by photosystem I. Partial irreversibility of P700 photooxidation at low temperatures and appearance of two components (rapid and slow) in the time course of P700+ dark reduction reflect the contribution of different acceptors in electron transport. Thermoinactivation of fragments incubation at acid pH or treatment by glutaraldehyde cause complete inhibition of irreversible P700 photooxidation and slow dark reduction of P700+ at -170 degrees. The slow component of P700+ reduction and irreversible photooxidation of P700 are ascribed to contribution of secondary ferredoxin acceptors. The accurence of rapid component of P700+ dark reduction in light induced signal of treated fragments indicate that this component is due to recombination of reduced primary acceptor and P700+. Because only one electron transport takes at -170 degrees, the occurence of rapid and slow components in dark decay kinetics of P700+ suggests, that secondary acceptors of some reaction centers are incapable to reduction at -170 degrees. The shape of temperature dependence curve of the slow P700+ reduction component is interpreted as an indication of the tunneling electron transport.

[Characteristics of photosystem I from grana thylakoids and from stroma lamellae]. / Kharakteristika fotosistemy i Iz tilakoidov grany i mezhgrannykh lamell khloroplastov.

Photochemical and spectral properties of photosystem I particles isolated from grana thylakoids and stroma lamellae of chloroplasts of higher plants are studied. The similarity of P700 content in these particles and the same dependence of P700+ reduction on temperature and the time course of variable fluorescence from artificial electron donors and acceptors indicate on the same type of reaction center for both photosystems I. Stroma particles have a higher rate of dark relaxation of variable fluorescence and a higher rate of dark reduction of P700+ at room temperature, than grana particles. Moreover, on the basis of data on low temperature fluorescence spectra, the stroma particles contain less shortwave chlorophyll a forms than grana particles. Thus, photosystem I from grana thylakoids and from stroma lamellae have the same type of reaction centers and can differ only by their nearest environment.

[Dependence of fluorescence spectra of chloroplasts from the activity of photosystem 2]. / Zavisimost' spektra fluorestsentsii khloroplastov ot aktivnosti fotosistemy 2.

By means of high sensitive spectrofluorometer the fluorescence spectra have been measured of normal chloroplasts and those with blocked photosystem 2 activity due to photoinhibition or treatment with 0.6 M tris-buffer. At room temperature fluorescence spectra of inactivated chloroplasts are similar to the spectrum of normal chloroplasts measured at low light intensity. Under excitation by intense light a decrease of intensity at 685 nm is appeared (about 3-4 times) in the fluorescence spectra of inactivated chloroplasts as compared to the spectrum of normal chloroplasts. The sharp intensity decrease of maxima at 685 and 695 nm (3-4 times) and small decrease at 680 and 730 nm (by 30-50%) are observed in low temperature fluorescence spectra of inactivated chloroplasts. Thus, the damage of photosystem 2 reaction centres is not accompanied by the preferential decrease of the only fluorescence band. The similarity of fluorescence difference spectra of chloroplasts distinguished by the state of photosystem 2 reaction centre, and the complex structure of difference spectra indicate that the variable fluorescence of chloroplasts during the induction is due to the emission of bulk chlorophyll alpha of the photosystem 2.

[Bacteriochlorophyll fluorescence changes related to the bacteriopheophytin photoreduction in the chromatophores of purple sulfur bacteria]. / Izmeneiia bykhoda fluorestsentsii bakteriokhlorofilla pri fotovosstanovlenii bakternofeofitina v khromatoforakh pur urnykh sernykh bakterii

It is shown that illumination of chromatophores of sulfur bacterium Chromatium minutissimum at Eh of the medium --200 mV divided by --620 mV (when the photooxidation of pigment P890 is completely inhibited) induces a decrease in bacteriochlorophyll fluorescence yield, reversible in the dark. Under these conditions a reversible photoreduction of bacteriopheophytin is detected (bleaching of absorption bands at 543 and 760 nm and development of a band at 650 nm), which is accompanied by a blue shift of the absorption band at 8 nm. As a possible interpretation of these effects the suggestion is made on the function of bacteriopheophytin as a primary electron acceptor in reaction centers of bacteria. The bacteriopheophytin photoreduction, followed by a decrease in fluorescence yield, is also observed in other sulfur bacteria, Thiocapsa roseopersicina and Ectothiorodospira shaposhnikovii, but it is not detected in nonsulfur bacteria, Rhodospirillum rubrum and Rhodopseudomonas spheroides. This is considered as an evidence for the difference in the functional organization of the reaction centers of these two groups of bacteria,