[Estimation of the Index Value of Dielectric Permeability inside the Membranes of Purple Bacteria].

The joint application of the precise X-ray data for isolated bacteriochlorophyll complexes of reaction centers and the fundamental formulae for the energy of interaction between two equal dipoles enabled us to suggest a new methodical approach for determination of the values of the index of dielectric permeability in the micro volume enclosing special pairs in Rhodobacter sphaeroides reaction centers. The most probable value for this parameter was thus determined within 1.66-1.76. This approach was generalized for the inner layer of the membranes of purple bacteria and yielded the index value about 1.70-1.85. It is argued that this range of dielectric permeability is adequate for bacterial and plant membranes as well. Low magnitude of this parameter contributes to higher efficiency of energy migration from vast light-harvesting chlorophyll "antenna" to the energy converting reaction centers and hence to higher efficiency of the whole photosynthesis.

[Endophytic Bacteria in Microbial Drugs that Improve Plant Development (Review)].

In this review data on the possibility of using endophytic bacteria for improving crop yields and quality are discussed.

Short-lived delayed luminescence of photosynthesizing organisms. II. The ratio between delayed and prompt fluorescence as studied by the modulation method.

The ratio between the intensities of delayed and prompt fluorescence was studied for different photosynthetic objects under different conditions by modulation method. The method is based on excitation of luminescing objects by light, modulated harmonically, and on a combined study of phase shifts and demodulation coefficients of the luminescence as related to excitation light. The presence of intense delayed emissions was revealed in purple bacteria, Ectothiorhodospira shaposhinokovii, Rhodospirillum rubrum and Rhodopseudomonas sphaeroides, in the micro- and nanosecond range. Under conditions of saturating light, their proportion was several percent of the total emission. The most striking phenomenon was observed under reducing conditions (addition of 1 . 10(-2) M Na2S2O4 to whole-cell suspensions of purple bacteria) where the intensity of the delayed emissions grew dramitically and became comparable to that of prompt fluorescence. The data obtained indicate that, at room temperature, reversal of some early stages of charge separation in bacterial reaction centres may proceed largely via the channel that includes generation of the reaction-centre bacteriochorophyll in the excited singlet state, followed by excitation-energy migration to antenna bacteriochlorophyll. The relation of these phenomena to the efficiency of solar energy utilization in photosynthetic apparatus is discussed.

Short-lived delayed luminescence of photosynthetic organisms. I. Nanosecond afterglows in purple bacteria at low redox potentials.

A combined study of emissions of purple bacteria Rhodospirillum rubrum, Ectothiorhodospira shaposhnikovii and Thiocapsa roseopersicina was performed under conditions of low potential. It has been shown that a considerable part of the emission represents a delayed luminescence with a lifetime of about 5 ns and an activation energy delta E = 0.05 +/- 0.03 eV. Intensity of this delayed luminescence is approximately equal to that of prompt fluorescence. It diminishes as temperature decreases and also as the intermediate acceptor I becomes reduced after prolonged illumination under low potential conditions. This luminescence represents a radiative decay of the intermediate state, PF, and the luminescence activation energy, delta E, reflects the energy barrier between P*-890 and PF. The value of this barrier determined in the present work is much lower than those obtained previously [3,4,26] for the free-energy release during the primary act of charge separation, basing on redox potential techniques. The reason for this discrepancy is discussed. Delayed luminescence in the picosecond time range is predicted to exist under conditions of active photosynthesis as a result of a small (approx. 0.05 eV) energy barrier between PF and the excited singlet state of reaction center bacteriochlorophyll.

The fractionation of plant photoactive pigment-protein complexes I and II.

The pigment-protein complexes enriched with Photosystem I (PPC-I) and Photosystem II (PPC-II) were obtained using sievorptive chromatography on DEAE-Sephadex column. Both types of complexes contain Chlorophyll a, beta-carotene and minor quantities of Chl b. Red absorbance maxima are located at 676 nm and 673 nm for PPC-I and PPC-II, respectively. The degrees of reaction centre enrichment were measured by the method of differential spectrophotometry: PPC-I has one P-700 per 35 bulk Chl a molecules, PPC-II contains one P-680 per 18 bulk Chl a molecules. The yield of PPC-II is 7--10 times lower than that of PPC-I. After one chromatographic procedure the amount of P-680 in PPC-I preparation does not exceed 7% of that of P-700, the amount of P-700 in PPC-II preparation 2% of that of P-680. The product of PPC-II degradation was studied.

Effect of mutations in Pisum sativum L. genes blocking different stages of nodule development on the expression of late symbiotic genes in Rhizobium leguminosarum bv. viciae.

In this report, the expression of late symbiotic genes (fnrN, fixN, and nifA) of Rhizobium leguminosarum bv. viciae was studied in nodules of mutant pea lines blocked at four successive stages of nodule development. Bacterial gene expression was analyzed in situ with transcriptional gusA reporter gene fusions. As a control, a constitutively expressed gusA gene was included. In the nodules of Nop(nodule persistence) mutants (mutant in gene sym13), which had not yet exhibited signs of premature senescence, the expression patterns observed were identical to those in wild-type nodules. Normal expression of fusions also occurred in nodules defective at the infection droplet differentiation stage (mutant in gene sym40) in which bacteria are endocytosed, but infection threads and infection droplets are hypertrophied. In contrast, in Itn- (infection thread formation inside the nodule tissue) mutants (mutant gene sym33), in which there is no endocytosis of bacteria, expression of the constitutive fusion was only in infection threads and no activity was shown for the other fusions. From this it can be concluded that functionality of the plant gene Sym33, i.e., bacterial endocytosis, is a prerequisite for the expression of late symbiotic genes in the microsymbiont. No morphologically distinct interzone II-III could be detected in nodules blocked at the bacteroid differentiation stage (mutants in gene sym31). The constitutive fusion was expressed equally throughout the nodule tissue (except for the meristem), and the activity of fusions to late symbiotic genes increased gradually with a maximal expression level at the base of the nodule. This is consistent with an altered oxygen barrier previously reported for these nodules. By including double mutants, earlier results on sequential functioning of gene pairs sym33-sym40 and sym31-sym13 could be confirmed and it could be demonstrated that the developmental epistasis found at the morphological level also is reflected in the expression pattern of late symbiotic genes in the microsymbiont.

Developmental downregulation of rhizobial genes as a function of symbiosome differentiation in symbiotic root nodules of Pisum sativum.

• The expression of nodA and dctA genes of Rhizobium leguminosarum bv. viciae has been studied in mutant nodules of pea (Pisum sativum L.), blocked at the following developmental stages: infection thread development inside the nodule (Itn); infection droplet differentiation (Idd); bacteroid differentiation after endocytosis (Bad); and nodule persistence (Nop). • With the use of reporter fusions to these symbiotic bacterial genes it was shown that both nodA and dctA were expressed at all developmental stages, with a pattern similar to that of constitutive, symbiosis-unrelated genes. • As well as two constitutively expressed genes, both nodA and dctA genes seemed to be subjected to gradual downregulation in nodule bacteria, correlating with the stage of bacteroid differentiation reached. No such effect was observed for the symbiotic, oxygen-regulated fixN gene. The bacteroid development stage also appeared to be related to the ability of bacteria that have been subjected to endocytosis to resume free-living vegetative growth. • The results support the suggestion that bacteroid differentiation into a nitrogen-fixing, organelle-like form, is a gradual process involving several stages, each controlled by different plant genes.

The revision of the model of primary energy conversion in purple bacteria.

A simulation method is suggested which enables one to check whether a model for excitation energy exchange in an ensemble of dye molecules fits available experimental data. In particular, this method may deal with photosynthetic units (PSUs) in which excitation migration in antenna chlorophylls and their substantial trapping in reaction centers (RCs) take place. Its application to the purple bacteria has proved that the model, which was generally accepted during the last 20-30 years, is in contradiction with recent experimental facts and thus requires modernization. Two physical mechanisms are discussed: femtosecond polarization of mobile hydrogen atoms near the reaction center special pair ("water latch"), and the presence of excitons delocalized over several core-bacteriochlorophylls (BChls). Our considerations give evidence that neither of these mechanisms alone can resolve the conflict, but their cumulative action appears to be sufficient. Unfortunately, these mechanisms were as yet only partially addressed experimentally.

Genetic dissection of Rhizobium-induced infection and nodule organogenesis in pea based on ENOD12A and ENOD5 expression analysis.

In legumes, perception of rhizobial lipochitooligosacharide-based molecules (Nod factors) and subsequent signal transduction triggers transcription of plant symbiosis-specific genes (early nodulins). We present genetic dissection of Nod factor-controlled processes in Pisum sativum using two early nodulin genes PsENOD12a and PsENOD5, that are differentially up-regulated during symbiosis. A novel set of non-nodulating pea mutants in fourteen loci was examined, among which seven loci are not described in Lotus japonicus and Medicago truncatula. Mutants defective in Pssym10, Pssym8, Pssym19, Pssym9 and Pssym7 exhibited no PsENOD12a and PsENOD5 activation in response to Nod factor-producing rhizobia. Thus, a conserved signalling module from the LysM receptor kinase encoded by Pssym10 down to the GRAS transcription factor encoded by Pssym7 is essential for Nod factor-induced gene expression. Of the two investigated genes, PsENOD5 was more strictly regulated; not only requiring the SYM10-SYM7 module, but also SYM35 (NIN transcription factor), SYM14, SYM16 and SYM34. Since Pssym35, Pssym14, Pssym34 and Pssym16 mutants show arrested infection and nodule formation at various stages, PsENOD5 expression seems to be essential for later symbiotic events, when rhizobia enter into plant tissues. Activation of PsENOD12a only requires components involved in early steps of signalling and can be considered as a marker of early symbiotic events preceding infection.

On the efficiency of the long wavelength minor bacteriochlorophyll groups in the vicinity of reaction centers.

The role of minor chlorophyll and bacteriochlorophyll groups in excitation delivery to reaction centers and subsequent trapping in them was analyzed by means of PC-modeling. The analysis of general type of photosynthetic units and, in particular, those resembling typical photosystems of purple bacteria, has revealed some types of structures in which the presence of minor BChl fractions in the vicinity of reaction centers did increase the efficiency of the useful energy trapping. In some cases the spectral range of optimal energy conversion is broadened.

Discrepancy between experimental and theoretical excitation transfer rates in LH2 bacteriochlorophyll-protein complexes of purple bacteria.

Discrepancy is revealed between the values of excitation transfer times measured experimentally, and those calculated, for the atomic structures of B800 --> B850 bacteriochlorophylls within the LH2 light-harvesting pigment-protein complex of the purple bacterium Rhodopseudomonas acidophila. The value 2.9-3.2 ps for the B800 --> B850 excitation transfer, calculated on the basis of atomic structure of LH2, is about 4-times longer than that measured for this bacterium (0.7 ps). This discrepancy appears common in at least two purple bacteria. Possible sources responsible for this discrepancy are discussed. It may either signify some drawback/s/ in our notions about the precise in vivo structure of LH2 complexes, for example, possible changes of LH2 structure during crystallization, or it may reflect our ignorance of some mechanisms involved in excitation migration.

Energy migration as related to the mutual position and orientation of donor and acceptor molecules in LH1 and LH2 antenna complexes of purple bacteria.

Many approaches to discovering the interaction energy of molecular transition dipoles use the well-known coefficient xi(phi, psi (1) psi (2)) = (cos phi - 3 cos psi (1) cos psi (2))(2), where phi, Psi (1), and Psi (2) are inter-dipole angles. Unfortunately, this formula often yields rather approximate results, in particular, when it is applied to closely positioned molecules. This problem is of great importance when dealing with energy migration in photosynthetic organisms, because the major part of excitation transfers in their chlorophyllous antenna proceed between closely positioned molecules. In this paper, the authors introduce corrected values of the orientation factor for several types of mutual orientation of molecules exchanging with electronic excitations for realistic ratios of dipole lengths and spacing. The corrected magnitudes of interaction energies of neighboring bacteriochlorophyll molecules in LH2 and LH1 light-absorbing complexes are calculated for the class of photosynthetic purple bacteria. Some advantageous factors are revealed in their mutual positions and orientations in vivo.

Transfer of excitation energy in photosynthesis: some thoughts.

The aim of the present paper is to aid biologists understand the complex physical problems of intramolecular energy transfer, in particular, between antenna (bacterio) chlorophyll molecules in vivo.The author has attempted, in the first part of the paper, to explain complicated processes of excitation transfer in a language understandable to readers with knowledge in fundamentals of general physics, but not in molecular optics.The second part of this paper is a critical review relevant to the specifics of physical theories and their applicability to the problem of energy transfer in antenna (bacterio) chlorophylls ((B) Chls) to reaction centers (RCs) in the photosynthetic organisms.