[Activation of the chloroplast respiration increases chlorophyll fluorescence yield in Chlorella adapted to darkness at higher temperature]. / Activatsiia khloroplastnogo dykhaniia uvelichivaet vykhod fluorestsentsii khlorofilla u Chlorella, adaptirovannoi k temnote pri povyshennoi temperature.

A tenfold increase in chlororespiration during dark incubation of Chlorella perynoidosa Chick at high temperature doubled the initial chlorophyll fluorescence yield (F0). The presence of iodacetamide or unmetabolizable glucose analog 2-deoxy-D-glucose prevented increase in both chlororespiration and F0 yield. The rates of chlororespiration and F0 yield growth demonstrated a similar pattern of temperature dependence. Inhibition of electron transport between QA and plastoquinone prevented increase in F0 during dark respiration of the cells at high temperature. Apparently, a pool of plastoquinone was restored in the chlororespiratory chain during the dark incubation at 37.5-41 degrees C and plastoquinone exchanged electrons with QA. This is the cause of QA reduction and subsequent increase in F0 yield.

[Photoinduced reactivation of photosystem II in Chlorella after prolong incubation without light]. / Svetoindutsirovannoe vosstanovlenie aktivnosti fotosistemy II u khlorelly posle dlitel'noi temnovoi inkubatsii.

The light-dependent reactivation of photosystem II in Chlorella pyrenoidosa Chick, CALU-175 cells, inactivated with supraoptimal temperatures (40-43 degrees C) in the dark or during heterotrophic growth was studied. It was shown that the inactivation of photosystem II after incubation in the dark at 41-42 degrees C, which showed up in the suppression of relative yield of variable chlorophyll fluorescence Fv due to an increase in yield F0 could be completely reversed by light. The inactivation of photosystem II at 43 degrees C in the dark could not be reversed by subsequent irradiation. In this case, the suppression of Fv/Fm was related not only to the growth of F0 but also with the decrease in Fm. The light dependences of the rate and extent of reactivation of yield Fv after heterotrophic growth or incubation of chlorella at 41 degrees C in the dark completely coincided. The full light-induced reactivation of photosystem II took place as the rate of photoinduced electron transport reached the rate of nonphotochemical reduction of plastoquinone in the dark. These results suggest that the light-reversed inactivation of photosystem II after heterotrophic growth or incubation at 41 degrees C in the dark is due to the redox-interaction of the primary quinone acceptor with plastoquinone reduced by the electron flux from the substrates of chlororespiration.

Two types of PS II centres as manifested by light saturation of delayed fluorescence from DCMU-treated chloroplasts.

Intensity of 2 s delayed fluorescence (DF) as a function of steady-state actinic light intensity was investigated in pea chloroplasts in the presence of 10 µM DCMU. The light saturation curve of DF was approximated by a sum of two hyperbolic components which differ by an order of magnitude in the half-saturating incident light intensity. The relative contribution of the amplitudes of the components was practically independent of cation (Na(+) and Mg(2+)) concentration and a short-term heating of the chloroplasts at 45°C. The component saturating at low incident light intensity was selectively suppressed by 100 µM DCMU or by 1 µmol µg(-1) Chl oleic acid. DF intensity following excitation by a single saturating 15 µs flash was equal to the intensity of the component saturating at a low incident light intensity. Upon flash excitation, the maximum steady-state DF level was found to be attained only after a series of saturating flashes. It is concluded that the two components of the DF light saturation curves are related to PS II centres heterogeneity in quantum yield of stabilization of the reduced primary quinone acceptor.

Multiple action sites for photosystem II herbicides as revealed by delayed fluorescence.

DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea) at concentrations higher than 10 µM suppresses the second time range delayed fluorescence (DF) of pea chloroplasts, due to inhibition of the oxidizing side of photosystem II (PS II). The inhibition of the reducing side of PS II resulting in the suppression of millisecond DF takes place at much lower (∼0.01 µM) DCMU concentrations. The variation in the herbicide-affinities of the reducing and oxidizing sides of PS II is not the same for DCMU and phenol-type herbicides. The DCMU-affinity of the oxidizing side considerably increases and approximates that of the reducing side upon mild treatment of chloroplasts with oleic acid. Probably this is a result of some changes in the environment of the binding site at the oxidizing side. At DCMU concentrations higher than 1 mM, the chaotropic action of DCMU leads to the generation of millisecond luminescence which is not related to the functioning of the reaction centres.

Enhancement of chloroplast energization in Chlorella by treatments inactivating the nitrate-reducing system.

Inactivation of the nitrate-reducing system in whole cells of Chlorella vulgaris Bejerinck by darkening, nitrogen starvation, ammonium, or cycloheximide brings cells into a state with a high yield of the millisecond-delayed fluorescence of chlorophyll. Activation of this system by illumination, by adding glucose to dark-adapted cells or nitrate to nitrogen-starved cells brings the cells into a low-yield state. The transitions between the lowand high-yield state induced by alternating light and dark periods are suppressed by tungstate and restored by subsequent molybdate addition. The drop in the delayed-fluorescence yield upon activation of the nitrate-reducing system is associated with the decrease of the amplitude of the electrochemical proton gradient across the thylakoid membrane of the chloroplast, as evidenced by the kinetics of the light-induced adsorption changes at 520 nm. The decrease of the proton gradient may be caused by the electron flow diverting from the cyclic path in photosystem I as a result of the activation of the electron transfer from ferredoxin to nitrite.

[Thermoluminescence and electric polarization in chloroplasts]. / Termoliuminestsentsiia i élektricheskaia poliarizatsiia v khloroplastakh.

Exposure of pea chloroplasts to electric field causes the appearance of a new thermoluminescence (TL) band at--(40-50) degrees C and a reduction of the intensity of its main bands. Extents of intensity drop are different for different components of TL and depend on the temperature of illumination. The charge traps responsible for the individual TL components seem to be localized in microsurroundings having different field susceptibility. The electric field effects observable at different temperatures are in correlation with the thermodepolarization currents which reflect the mobility and number of charged groups undergoing a field-induced displacement in chloroplast membranes. Dehydration. of chloroplast film preparations causes a reduction in the intensities of the TL peaks and thermodepolarization currents and a shift of the peaks positions toward higher temperatures. It is assumed that the traps of the recombining charges have two different conformations, each with its own frequency factor for the recombination reaction. Changes in the thermoluminescence behavior in applied electric field are due to the polarization of the traps, which increases the existence probability of a conformation with a high frequency factor.

Effects of pH and deuterium oxide on the heat-inactivation temperature of chloroplasts.

The inactivation temperature for Hill activity and for the long-lived delayed fluorescence of isolated Pisum sativum L. chloroplasts was found to depend on pH, the maximal value being in the pH region 5-7. Salts increase the inactivation temperature by 4-7°C. Effects of D2O and some other substances that modify the thermostability of chloroplasts are dependent on pH. It is concluded that thermal denaturation of proteins is the most probable mechanism for heat inactivation of chloroplasts.

The mechanisms of fatty-acid inhibition of electron transport in chloroplasts.

Unsaturated fatty acids at concentrations of 1-2 µmol mg(-1) chlorophyll decrease the intensity of long-lived delayed fluorescence and inhibit the Hill reaction in Pisum sativum L. chloroplasts in a pH-dependent and reversible manner. A charged form of the fatty acids is two times more effective than an undissociated form. Fatty acids, anionic and cationic detergents and urea inhibit activity and decrease the temperature of heat inactivation of the water-spilitting system. Sucrose at a concentration of 2.5 M protects chloroplasts against the effects of these compounds. It is concluded that their action can be explained by the denaturation of the water-splitting protein.

[Interaction between the fluorescent probe 1-anilino-naphthalene-8-sulfonate and chloroplasts]. / Vzaimodeistvie fluorestsentnogo zonda 1-anilinonaftalin-8-sul'fonata s khloroplastami.

Interaction between fluorescent probe 1-anilino-naphthalene-8-sulphonate (ANS) and chloroplasts was studied. Parameters of ANS binding with membranes and weakly-bound proteins of chloroplasts were determined. It has been shown that at all pH values the increase of quantum yield of ANS fluorescence with the addition of chloroplasts is mainly determined by the interaction between the probe and weakly-bound chloroplast proteins.

[Effect of pH and substitution of H2O for D2O on oxygen liberation by chloroplasts]. / Vliianie pH i zameshcheniia H2O na D2O na vydelenie kisloroda khloroplastami.

The rate of dark relaxation of the oxygen evolving system in chloroplasts is shown to depend on the value of the surface charge of some chloroplast membrane component having protein nature and isoelectric point at pH 6.0. The substitution of H2O for D2O leads to isoelectric point shift of this protein.

Photosynthetic Apparatus Formation during the Cell Cycle of Chlorella.

Synchronous cell division in cultures of Chlorella vulgaris Beijerinck was induced by intermittent illumination: 9 hours light, 6 hours darkness. The rate of photosynthetic O(2) evolution per cell increases 4-fold in a one-step manner at the beginning of the light period, to the same extent as the increase in cell number. Over the division cycle, the following accumulation times during the light period were found: chlorophyll a, between 2 and 8 hours, chlorophyll b, between 5 and 8 hours, reaction centers of photosystems I and II, between 2 and 6 hours; and cytochrome f, between 2.5 and 5 hours. Cytochrome f accumulation is closely followed by an increase in amplitude of the rapid phase in light-induced absorption increase at 520 nanometers and in intensity of the delayed light emission. Enhancement of the delayed fluorescence yield per flash under continuous illumination (caused by the establishment of the pH difference across the thylakoid membrane) is maximal by the first hour of the light period.These findings, and others described in the text, suggested that the 4-fold growth of photosynthetic apparatus in the course of the cell cycle cannot be the result of gradual rise of electron-transport chain number. Rather, it is the result of a series of successive syntheses of its individual components. The rate-limiting step of electron transport is probably located between plastoquinone and cytochrome f.

[Pigment degradation in Synechocystis aquatilis under nitrogen starvation with varying illumination]. / Degradatsiia pigmentov u Synechochystis aquatilis v usloviiakh azotnogo golodanii pri razlichnoi osveshchennosti.

When the cells of Synechocystis aquatilis are incubated in a medium without nitrogen, the degradation of pigments in the conditions of illumination occurs in two stages: (i) during the first day and (ii) after three days of the incubation. The degree of degradation increases with the intensity of illumination and correlates with the rate of cell death. The pigments are not degraded in the dark. When chlorotic cells are transferred to a medium containing nitrogen, their number increases stepwise by a factor of 1.2 after 7--8 hours and rises exponentially after 14 hours; the synthesis of phycocyanin starts after 7 hours and the synthesis of chlorophyll only after 12 hours when the chlorophyll-to-phycocyanin ratio reaches its normal value (1. 1).

The influence of the electric diffusion potential on delayed fluorescence light curves of chloroplasts treated with 3-(3,4-dichlorophenyl)-1,1-dimethylurea.

The potassium salt-induced transient increase of delayed fluorescence yield was studied in pea chloroplasts treated with 3-(3,4-dichlorophenyl)-1,1-dimethylurea. A simple kinetic model is proposed to account for the actinic light intensity dependence of the delayed fluorescence enhancement by the transmembrane diffusion potential induced by sudden salt addition. The electric field dependence of the rate constants for the recombination of primary separated charges with and without subsequent electronic excitation of reaction center chlorophyll was obtained. From the value of enhancement of delayed fluorescence by salt concentration gradients at saturating actinic light intensity, it is concluded that the distance, normal to thylakoid membrane surface, between the primary acceptor and the donor of Photosystem II is smaller than the membrane thickness.

Temperature dependence of the delayed fluorescence from wheat leaves treated with 3-(3,4-dichlorophenyl)-1-1,-dimethylurea.

Light saturation curves of the delayed fluorescence of wheat leaves treated with 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) were measured at different temperatures. Calculated activation energies for a half-saturation actinic light intensity and saturated delayed fluorescence emission were 0.89 and 0.32 eV, respectively. On the basis of the kinetic model energy levels of Photosystem II reaction center components were estimated.

[Conformational kinetic model of the functioning of the photosynthetic reaction center]. / Kineticheskaia model' funktsionirovaniia fotosinteticheskogo reaktsionnogo tsentra, uchityvaiushchaia ego konformatsionnye sostoianiia.

A model for stabilization of separated charges in the pigment-protein complex of the photosynthetic reaction center (RC) in purple bacteria is proposed. Alongside with ordinary electron transfers, the model involves conformational transitions in the pigment-protein complex. Based on the proposed model, an estimation of basic parameters of conformational mobility of RC protein complexes is made.

[Possible role of macromolecular components in the functioning of photosynthetic reaction centers of purple bacteria]. / O vozmozhnoi roli makromolekuliarnykh komponentov v funktsionirovanii fotosinteticheskikh reaktsionnykh tsentrov purpurnykh bakterii.

The temperature dependencies of the photoconversion of pigments P870--P890 were studied using isolated chromatophores and photosynthetic reaction centres (RC's) of purple bacteria. The samples were prepared by extraction with organic solvents (light petroleum and a combination of light petroleum and methanol) and modified through cross-linking the functional groups of proteins by treatment with glutaraldehyde or denatured by various physical and chemical treatments. The data provide further evidence that the pool of RC secondary acceptors is formed by the compounds of quinone nature located in the hydrophobic surrounding. Similar molecules localized in a more polar medium act as primary acceptors. The findings indicate on the essential role of macromolecular components in the RC's functioning and also suggest that the photochemical charge separation is conformation-controlled.