Trapped modes in particles with a negative refractive index.

The natural oscillations of the electromagnetic field in a particle made from left-handed metamaterial, where both permittivity and permeability are negative, are considered. Based on the exact solution of the sourceless Maxwell equations, it is shown that due to the opposite directions of the phase and group velocities in the metamaterial, natural oscillations in such particles decay exponentially at infinity, that is, these natural oscillations can be considered as trapped modes with a finite energy. The manifestation of such modes in experiments with Bessel beams is also discussed.

[Choice of an alternative access in failed endovascular intervention through the right radial artery]. / Vybor al'ternativnogo dostupa pri neudache éndovaskuliarnogo vmeshatel'stva cherez pravuiu radial'nuiu arteriiu.

The transradial access has deservedly become the 'gold standard' while performing various X-ray endovascular interventions both diagnostic and therapeutic ones. However, along with all its advantages, it is not without disadvantages. These difficulties for the most part are related to peculiarities of the anatomy of upper-limb arteries. It is exactly complex anatomy that is the most common cause of complications and compelled change of the access while using the right radial artery. The purpose of our study was to examine the symmetry of complex anatomy of upper-limb arteries in order to choose an optimal and safe way of conversion of the access in case of forced refusal from the right radial access. For this reason there was developed an open multicentre registry acronymized as COMPAAS (COMPlex Anatomy of Arteries and Symmetry). During the work of this Registry from February to December 2018, correspondents of the study became 35 colleagues from 23 clinics of 11 cities of Russia. The working group analysed a total of 127 patients presenting with 157 variants of complex anatomy of lower limb arteries: high bifurcation of the radial artery (84), complete loop or tortuosity (66), and compartmental calcification of brachial arteries (7). The anatomy of arteries on the opposite upper extremity was studied based on angiographic findings. The most frequent variant (84 cases) of complex anatomy was high bifurcation of the radial artery at the level of the a. brachialis (20.9% of cases), with the origin of the brachial artery at the level of the a. axillaris being revealed half as often (9.9%). The maximum percentage of symmetry was observed in the group of patients presenting with compartmental calcification of upper-limb arteries (85.7%). Complete loop or marked (more than 100°) tortuosity of arteries on both arms was revealed in 54% of cases. Besides, in 25% of cases, tortuosity was combined with the high origin of the radial artery. It is noteworthy that none of the 127 patients appeared to have complex anatomy on the a. ulnaris. When revealing pronounced calcification of arteries of the forearm or a combination of high bifurcation with tortuosity, it seems feasible to decide upon conversion of the access to the femoral one (a. femoralis) or ulnar (a. ulnaris). In isolated high bifurcation on the right, effective conversion to the contralateral (left) radial approach is possible in not less than 75% of cases.

[Effectiveness of intraoperative monitoring of motor evoked potentials for predicting changes in the neurological status of patients with cervical spinal cord tumors in the early postoperative period]. / Éffektivnost' intraoperatsionnogo monitoringa motornykh vyzvannykh potentsialov pri prognozirovanii dinamiki nevrologicheskogo statusa v rannem posleoperatsionnom periode u patsientov s opukholiami sheinogo otdela spinnogo mozga.

AIM: The study aim was to evaluate the effectiveness of intraoperative monitoring of motor evoked potentials (MEPs) for predicting changes in the neurological status of patients with cervical spinal cord tumors in the early postoperative period. MATERIAL AND METHODS: The study included 74 patients with intradural cervical spinal cord tumors who were operated on using motor evoked potential monitoring in the period from 2013 to 2016. There were 29 (39%) males and 46 (61%) females. Group 1 included 26 (35%) patients with intramedullary tumors; group 2 included 48 (65%) patients with intradural extramedullary tumors. The neurological status was assessed by using a six-grade muscle power MRC scale; a modified McCormick scale was used to evaluate the functional status. Transcranial electrical stimulation of the precentral gyri was performed. Recording electrodes were located in the peripheral target muscles of the upper and lower limbs. Total intravenous anesthesia with propofol and fentanyl was used. RESULTS: In Group 1, MEPs decreased in 19 (73%) of 26 patients; MEPs remained unchanged in 7 (27%) patients. Among the patients with decreased MEPs, 14 (74%) patients had postoperative deterioration of the neurological status; 6 (32%) patients had a preoperative severe neurological deficit; 4 (21%) patients had no changes in the neurological status. The sensitivity and specificity of MEPs from the upper limb muscles were higher than those from the lower limb muscles. In Group 2, improvement of the neurological status occurred in all 48 patients. There was no case of a true positive decrease in the MEP amplitude. CONCLUSIONS: 1. Registration of MEPs is a highly sensitive and highly specific method for diagnosing corticospinal tract dysfunction in patients with intramedullary tumors of the cervical spinal cord. The sensitivity and specificity of MEPs recorded from the upper limbs are higher than those from the lower limb muscles. 2. The sensitivity of MEPs in patients with extramedullary intradural tumors was 0%, the diagnostic effectiveness of MEPs amounted to 86% from the upper limb muscles and 93% from the lower limb muscles. 3. When the MEP amplitude in patients with extra- and intramedullary tumors of the cervical spinal cord decreases, a change in the surgion's approach may reduce or completely eliminate surgically-induced damage to the spinal cord.

[Syringosubarachnoid shunting in treatment of syringomyelia: a literature review and a clinical case report]. / Siringosubarakhnoidal'noe shuntirovanie v lechenii siringomielii: obzor literatury i illiustratsiia klinicheskogo sluchaia.

In the article, we describe a clinical case of syringomyelia associated with an Arnold-Chiari type 1 malformation, evaluate the efficacy of syringosubarachnoid shunting, and analyze the literature data of domestic and international researchers involved in investigation and treatment of the pathology. Application of syringosubarachnoid shunting in the described case resulted in a clinical improvement in the form of regression of paresis and hypoesthesia, which demonstrated the efficacy of the shunting technique for correction of the syringomyelia symptoms.

[Impact of sagittal balance parameters on life quality in elderly and senile patients after surgery for degenerative lumbar spine stenosis]. / Vliianie parametrov sagittal'nogo balansa na kachestvo zhizni u patsientov pozhilogo i starcheskogo vozrasta, operirovannykh po povodu degenerativnogo stenoza poiasnichnogo otdela pozvonochnika.

INTRODUCTION: As the life span and proportion of people over 65 years increase, the incidence of degenerative lumbar spine stenosis grows proportionally. Various parameters of the spinopelvic relationships are used to predict surgical treatment outcomes in patients with degenerative spine diseases. There are no unified protocols for evaluation, in terms of the sagittal balance, of surgical treatment outcomes in elderly patients. PURPOSE: To study the impact of sagittal balance parameters on the life quality of elderly and senile patients after surgery for degenerative stenosis of the lumbar spine. MATERIAL AND METHODS: The study included 109 patients. Decompression was performed in the first group of 53 patients. Decompression and stabilization were performed in the second group of 27 patients. In the third group of 29 patients, XLIF indirect decompression, scoliosis correction, reconstruction of disturbed spinopelvic relationships, and stabilization were carried out. We evaluated the following sagittal balance parameters: pelvic incidence (PI), sacral slope (SS), pelvic tilt (PT), lumbar lordosis (LL), and PI minus LL (PI-LL). The quality of life indicators were assessed using VAS, ODI, and SF36 scores. RESULTS: In the first group, there were not statistically significant differences for PT≤20° and PT>20°. A statistically significant change in the PI-LL parameter (p=0.0263) was in the first group. A decrease in PI-LL was accompanied by regression of pain (p<10-4). In the second group, comparison of the quality of life indicators revealed no statistically significant differences between PT≤20° and PT>20° as well as PI-LL≤10° and PI-LL>10 in the postoperative period. In the third group, postoperative improvement in PT (p=0.0002) and PI-LL (p=0.0008) parameters was accompanied by a decrease in pain in the legs (p=0.0002) and lumbar spine (p=0.0001). CONCLUSION: Improvement in the quality of life indicators in 48.6% of cases was achieved by decompression only; the sagittal balance parameters had no significant impact on quality of life. In 24.8% of cases, improvement in the quality of life indicators was achieved by decompression and stabilization because the dominant clinical neurological syndrome was instability. Reduced quality of life in 26.6% of patients was caused by disturbed spinopelvic relationships. Application of the XLIF technique in these patients provides statistically significant restoration of the sagittal balance parameters, PT and PI-LL, which improves quality of life.

Direct Measurements of Magnetic Polarons in Cd1-xMnxSe Nanocrystals from Resonant Photoluminescence.

In semiconductors, quantum confinement can greatly enhance the interaction between band carriers (electrons and holes) and dopant atoms. One manifestation of this enhancement is the increased stability of exciton magnetic polarons in magnetically doped nanostructures. In the limit of very strong 0D confinement that is realized in colloidal semiconductor nanocrystals, a single exciton can exert an effective exchange field Bex on the embedded magnetic dopants that exceeds several tesla. Here we use the very sensitive method of resonant photoluminescence (PL) to directly measure the presence and properties of exciton magnetic polarons in colloidal Cd1-xMnxSe nanocrystals. Despite small Mn2+ concentrations (x = 0.4-1.6%), large polaron binding energies up to ∼26 meV are observed at low temperatures via the substantial Stokes shift between the pump laser and the resonant PL maximum, indicating nearly complete alignment of all Mn2+ spins by Bex. Temperature and magnetic field-dependent studies reveal that Bex ≈ 10 T in these nanocrystals, in good agreement with theoretical estimates. Further, the emission line widths provide direct insight into the statistical fluctuations of the Mn2+ spins. These resonant PL studies provide detailed insight into collective magnetic phenomena, especially in lightly doped nanocrystals where conventional techniques such as nonresonant PL or time-resolved PL provide ambiguous results.

Two pathways of photoproduction of organic hydroperoxides on the donor side of photosystem 2 in subchloroplast membrane fragments.

Earlier the catalase-insensitive formation of organic hydroperoxides (via the interaction of organic radicals produced due to redox activity of P680+· (or TyrZ·) with molecular oxygen) has been found in Mn-depleted PS2 preparations (apo-WOC-PS2) by Khorobrykh et al. (Biochemistry 50:10658-10665, 2011). The present work describes a second pathway of the photoproduction of organic peroxides on the donor side of PS2. It was shown that illumination of CaCl2-treated PS2 membranes (deprived of the PS2 extrinsic proteins without removal of the Mn-containing water-oxidizing complex) (CaCl2-PS2) led to the photoproduction of highly lipophilic organic hydroperoxides (LP-OOH) (in amount corresponding to 1.5 LP-OOH per one reaction center of PS2) which significantly increased upon the addition of exogenous electron acceptor potassium ferricyanide (to 4.2 LP-OOH per one reaction center). Addition of catalase (200 U/ml) before illumination inhibited ferricyanide-induced photoproduction of hydroperoxides while no effect was obtained by adding catalase after illumination or by adding inactivated catalase before illumination. The hydroperoxide photoproduction was inhibited by the addition of exogenous electron donor for PS2, diphenylcarbazide or diuron (inhibitor of the electron transfer in PS2). The addition of exogenous hydrogen peroxide to the CaCl2-PS2 led to the production of highly lipophilic organic hydroperoxides in the dark (3.2 LP-OOH per one reaction center). We suggest that the photoproduction of highly lipophilic organic hydroperoxides in CaCl2-PS2 preparations occurs via redox activity of H2O2 produced on the donor side of PS2.

[CONSTRUCTION OF A TEST-SYSTEM WITH NANOPARTICLES OF COLLOID SILVER FOR DETECTION OF PSEUDOTUBERCULOSIS AND INTESTINAL YERSINIOSIS FOR CAUSATIVE AGENTS IN DOT-IMMUNOASSAY].

AIM: Construction of an immunologic test-system for detection of causative agents of enteropathogenic Yersinia (Yersinia pseudotuberculosis and Y. enterocolitica) by dot-immunoassay. MATERIALS AND METHODS: Nenoparticles of colloid silver sized 5-9 nm were used as a marker of specific antibodies. IgG fraction was isolated from commercial antisera to Y. pseudotuberculosis (Ο:1) and Y. enterocolitica (Ο:3 and Ο:9). Testing of the obtained test-system was carried out on 20 strains of Y.pseudotuberculosis and Y. enterocolitica (10 of each species). RESULTS: Dot-analysis had a specific character and detected enteropathogenic Yersinia at a level of 5-105 - 8.106 CFU/ml (100 - 1000 CFU in sample). Wherein cross-reaction with heterologic studied microorganisms - Escherichia coli, Salmonella typhimurium, Shigella flexneri, Yersina pestis EV - as not observed. A possibility of simultaneous detection and serotyping of Y. enterocolitica is shown, that is necessary for confirmation of their epidemic significance. CONCLUSION: The developed test-systems allow to study micro volumes of the samples under study (1 µ1), are express (1.5 - 2h), highly sensitive and specific, technically simple and do not require the use of high-cost equipment, special training of the staff, may be successfully used in practical healthcar in laboratories with varying equiptment levels.

Trehalose protects Mn-depleted photosystem 2 preparations against the donor-side photoinhibition.

Recently, it has been shown that the addition of 1M trehalose leads to the increase of the rate of oxygen photoconsumption associated with activation of electron transport in the reaction center of photosystem 2 (PS2) in Mn-depleted PS2 membranes (apo-WOC-PS2) [37]. In the present work the effect of trehalose on photoinhibition of apo-WOC-PS2 preparations (which are characterized by a high sensitivity to the donor side photoinhibition of PS2) was investigated. The degree of photoinhibition was estimated by the loss of the capability of exogenous electron donor (sodium ascorbate) to reactivate the electron transport (measured by light-induced changes of chlorophyll fluorescence yield (∆F)) in apo-WOC-PS2. It was found that 1M trehalose enhanced the Mn2+-dependent suppression of photoinhibition of apo-WOC-PS2: in the presence of trehalose the addition of 0.2µM Mn2+ (corresponding to 2 Mn2+ per one reaction center) was sufficient for an almost complete suppression of the donor side photoinhibition of the complex. In the absence of trehalose it was necessary to add 100µM Mn2+ to achieve a similar result. The effect of trehalose was observed during photoinhibition of apo-WOC-PS2 at low (15µmolphotons-1m-2) and high (200µmolphotons-1m-2) light intensity. When Mn2+ was replaced by other PS2 electron donors (ferrocyanide, DPC) as well as by Ca2+ the protective effect of trehalose was not observed. It was also found that 1M trehalose decreased photoinhibition of apo-WOC-PS2 if the samples contained endogenous manganese (1-2 Mn ions per one RC was enough for the maximum protection effect). It is concluded that structural changes in PS2 caused by the addition of trehalose enhance the capability of photochemical reaction centers of apo-WOC-PS2 to accept electrons from manganese (both exogenous and endogenous), which in turn leads to a considerable suppression of the donor side photoinhibition of PS2.

Enhancement of photoassembly of the functionally active water-oxidizing complex in Mn-depleted photosystem II membranes upon transition to anaerobic conditions.

It has been shown earlier (Khorobrykh and Klimov, 2015) that molecular oxygen is directly involved in the general mechanism of the donor side photoinhibition of photosystem II (PSII) membranes. In the present work the effect of oxygen on photoassembly ("photoactivation") of the functionally active inorganic core of the water-oxidizing complex (WOC) in Mn-depleted PSII preparations (apo-WOC-PSII) in the presence of exogenous Mn(2+), Ca(2+) as well as ferricyanide was investigated. It was revealed that the efficiency of the photoassembly of the WOC was considerably increased upon removal of oxygen from the medium during photoactivation procedure using the enzymatic oxygen trap or argon flow. The lowering of O2 concentration from 250µM to 75µM, 10µM and near 0µM results in 29%, 71% and 92%, respectively, stimulation of the rate of O2 evolution measured after the photoactivation. The increase in the intensity of light used during the photoactivation was accompanied by a decrease of both the efficiency of photoassembly of the WOC and the stimulation effect of removal of O2 (that may be due to the enhancement of the processes leading to the photodamage to PSII). It is concluded that the enhancement in photoactivation of oxygen-evolving activity of apo-WOC-PSII induced by oxygen removal from the medium is due to the suppression of the donor side photoinhibition of PSII in which molecular oxygen can be involved.

Manipulation of polarization and spatial properties of light beams with chiral metafilms.

Two-dimensional lattices of chiral nanoholes in a plasmonic film with lattice constants being slightly larger than light wavelength are proposed for effective control of polarization and spatial properties of light beams. Effective polarization conversion and strong circular dichroism in non-zero diffraction orders in these chiral metafilms are demonstrated by electromagnetic simulations. These interesting effects are found to result from interplay between radiation pattern of single chiral nanohole and diffraction pattern of the planar lattice, and can be manipulated by varying wavelength and polarization of incoming light as well as period of metastructure and refractive indexes of substrate and overlayer. Therefore, this work offers a novel paradigm for developing planar chiral metafilm-based optical devices with controllable polarization state, spatial orientation and intensity of outgoing light.

[A change in the sagittal balance in elderly and senile patients with degenerative stenosis of the lumbar spine].

Degenerative-dystrophic changes in the spine have general nature, which leads to changes in the balance parameters and consequently, other elements of the musculoskeletal systems. This article is devoted to analysis of the literature data, based on which we conclude that changes in the sagittal balance in elderly and senile patients as the restabilization stage still remain unexpected.

The green alga Chlamydomonas reinhardtii as a tool for in vivo study of site-directed mutations in PsbO protein of photosystem II.

The photosynthetic water oxidation in photosystem II (PS II) takes place in a special water-oxidizing complex (WOC) that consists of a catalytic center, Mn4CaO5 cluster, and also includes a group of extrinsic proteins needed for its stability. The most important of these is PsbO, which binds to the donor side of PS II near the Mn cluster and is directly involved in the regulation of its stability and activity. However, the molecular mechanism of PsbO involvement in photosynthetic water oxidation remains unclear. One of the main approaches to solving this problem is site-directed mutagenesis. Until recently, the effect of mutations in PsbO in vivo has been studied only in cyanobacteria (prokaryotes). In eukaryotic organisms, such studies (site-directed mutagenesis of PsbO) have not been carried out, though it is known that the role of PsbO protein in plants and cyanobacteria may be different. In this review, we consider the possibility of using for this purpose the unicellular green alga Chlamydomonas reinhardtii, a eukaryotic organism with a set of extrinsic proteins of the WOC similar to that of the higher plants. However, in contrast to higher plants, the ΔpsbO mutant of C. reinhardtii is viable. Another reason to use this alga is that the ΔpsbO strain of C. reinhardtii grown in the dark (heterotrophically) is able to build the minimal photochemically active complex of PS II, allowing investigation of the role of individual amino acid substitutions in PsbO in vivo without damaging PS II due to photoinactivation.

Trehalose stimulation of photoinduced electron transfer and oxygen photoconsumption in Mn-depleted photosystem 2 membrane fragments.

It is known that the removal of manganese from the water-oxidizing complex (WOC) of photosystem 2 (PS2) leads to activation of oxygen photoconsumption (OPC) [Khorobrykh et al., 2002; Yanykin et al., 2010] that is accompanied by the formation of organic hydroperoxides on the electron-donor side of PS2 [Khorobrykh et al., 2011]. In the present work the effect of trehalose on the OPC in Mn-depleted PS2 preparations (apo-WOC-PS2) was investigated. A more than two-fold increase of the OPC is revealed upon the addition of 1M trehalose. Drastic (30%-70%) inhibition of the OPC upon the addition of either electron acceptor or electron donor indicates that the trehalose-induced activation of the OPC occurs on both donor and acceptor sides of PS2. A two-fold increase in the rate of superoxide-anion radical photoproduction on the electron-acceptor side of PS2 was also shown. Applying the "variable" chlorophyll fluorescence (ΔF) it was shown that the addition of trehalose induces: (i) a significant increase in the ability of exogenous Mn(2+) to donate electrons to the reaction center of PS2, (ii) slowing down the photoaccumulation of the primary quinone electron acceptor of PS2 (QA(-)) under aerobic conditions, (iii) acceleration of the reoxidation of QA(-) by QB (and by QB(-)) as well as the replacement of QB(2-) by a fully oxidized plastoquinone, and (iv) restoration of the electron transfer between the quinone electron carriers in the so-called "closed reaction centers of PS2" (their content in the apo-WOC-PS2 is 41%). It is suggested that the trehalose-induced increase in efficiency of the O2 interaction with the electron-donor and electron-acceptor sides of apo-WOC-PS2 is due to structural changes leading to both a decrease in the proportion of the "closed PS2 reaction centers" and an increase in the electron transfer rate in PS2.

Involvement of molecular oxygen in the donor-side photoinhibition of Mn-depleted photosystem II membranes.

It has been shown by Khorobrykh et al. (Biochemistry (Moscow) 67:683-688, 2002); Yanykin et al. (Biochim Biophys Acta 1797:516-523, 2010); Khorobrykh et al. (Biochemistry 50:10658-10665, 2011) that Mn-depleted photosystem II (PSII) membrane fragments are characterized by an enhanced oxygen photoconsumption on the donor side of PSII which is accompanied with hydroperoxide formation and it was suggested that the events are related to the oxidative photoinhibition of PSII. Experimental confirmation of this suggestion is presented in this work. The degree of photoinhibition was determined by the loss of the capability of exogenous electron donors (Mn(2+) or sodium ascorbate) to the reactivation of electron transport [measured by the light-induced changes of chlorophyll fluorescence yield (∆F)] in Mn-depleted PSII membranes. The transition from anaerobic conditions to aerobic ones significantly activated photoinhibition of Mn-depleted PSII membranes both in the absence and in the presence of exogenous electron acceptor, ferricyanide. The photoinhibition of Mn-depleted PSII membranes was suppressed upon the addition of exogenous electron donors (Mn(2+), diphenylcarbazide, and ferrocyanide). The addition of superoxide dismutase did not affect the photoinhibition of Mn-depleted PSII membranes. It is concluded that the interaction of molecular oxygen (rather than superoxide anion radical formed on the acceptor side of PSII) with the oxidized components of the donor side of PSII reflects the involvement of O2 in the donor-side photoinhibition of Mn-depleted PSII membranes.

Eigen oscillations of a chiral sphere and their influence on radiation of chiral molecules.

Eigenmodes of a chiral sphere placed in a dielectric medium were investigated in details. Excitation of these eigenmodes by a plane wave and a chiral molecule radiation was studied both analytically and numerically. It was found that decay rates of "right" and "left" enantiomers are different in the presence of the chiral sphere. Strong dependence of radiation pattern of the chiral molecule placed in the vicinity of the chiral sphere on chirality strength was also demonstrated. An interesting correlation between chirality of sphere and spatial spirality (helicity, vorticity ...) of the electromagnetic fields in the presence of chiral sphere was observed for the first time.

Oxylipins and plant abiotic stress resistance.

Oxylipins are signaling molecules formed enzymatically or spontaneously from unsaturated fatty acids in all aerobic organisms. Oxylipins regulate growth, development, and responses to environmental stimuli of organisms. The oxylipin biosynthesis pathway in plants includes a few parallel branches named after first enzyme of the corresponding branch as allene oxide synthase, hydroperoxide lyase, divinyl ether synthase, peroxygenase, epoxy alcohol synthase, and others in which various biologically active metabolites are produced. Oxylipins can be formed non-enzymatically as a result of oxygenation of fatty acids by free radicals and reactive oxygen species. Spontaneously formed oxylipins are called phytoprostanes. The role of oxylipins in biotic stress responses has been described in many published works. The role of oxylipins in plant adaptation to abiotic stress conditions is less studied; there is also obvious lack of available data compilation and analysis in this area of research. In this work we analyze data on oxylipins functions in plant adaptation to abiotic stress conditions, such as wounding, suboptimal light and temperature, dehydration and osmotic stress, and effects of ozone and heavy metals. Modern research articles elucidating the molecular mechanisms of oxylipins action by the methods of biochemistry, molecular biology, and genetics are reviewed here. Data on the role of oxylipins in stress signal transduction, stress-inducible gene expression regulation, and interaction of these metabolites with other signal transduction pathways in cells are described. In this review the general oxylipin-mediated mechanisms that help plants to adjust to a broad spectrum of stress factors are considered, followed by analysis of more specific responses regulated by oxylipins only under certain stress conditions. New approaches to improvement of plant resistance to abiotic stresses based on the induction of oxylipin-mediated processes are discussed.

Interaction of molecular oxygen with the donor side of photosystem II after destruction of the water-oxidizing complex.

Photosystem II (PSII) is a pigment-protein complex of thylakoid membrane of higher plants, algae, and cyanobacteria where light energy is used for oxidation of water and reduction of plastoquinone. Light-dependent reactions (generation of excited states of pigments, electron transfer, water oxidation) taking place in PSII can lead to the formation of reactive oxygen species. In this review attention is focused on the problem of interaction of molecular oxygen with the donor site of PSII, where after the removal of manganese from the water-oxidizing complex illumination induces formation of long-lived states (P680(+•) and TyrZ(•)) capable of oxidizing surrounding organic molecules to form radicals.

Bicarbonate stimulates the electron donation from Mn²âº to P680⁺ in isolated D1/D2/cytochrome b559 complex.

Influence of bicarbonate on the efficiency of the electron donation from Mn(2+) to P680(+) in isolated D1/D2/cytochrome b559 complex was investigated. All the experiments were carried out in a medium depleted of HCO3(-)/CO2. Kinetics of photoinduced absorbance changes (ΔA) at different wavelengths and decrease of chlorophyll fluorescence yield (-ΔF) related to photoaccumulation of reduced pheophytin, the intermediary electron acceptor of photosystem II (PSII), in the presence of Mn(2+) under anaerobic conditions were measured. Addition of bicarbonate (1 mM) increased the amplitude of these ΔA and -ΔF at least by a factor of 3. Measurements of the photoinduced ΔA, related to photooxidation of the primary electron donor of PSII, chlorophyll P680, were done in the presence of silicomolybdate as electron acceptor. These results show that the addition of 0.05 mM Mn(2+) alone or jointly with 1 mM bicarbonate induces a 20% and 70%-decrease of the magnitude of the ΔA at 680 nm. The effect of Mn(2+) (in the presence and absence of bicarbonate) was completely eliminated by the addition of 12 mM EDTA. All these bicarbonate effects were not observed if MgCl2 or formate were used instead of MnCl2 and bicarbonate, respectively. In the absence of Mn(2+), bicarbonate induced none of the mentioned above effects (increase of photoaccumulation of reduced pheophytin and decrease of photooxidation of P680). The presented data suggest that bicarbonate stimulates the electron donation from Mn(2+) to D1/D2/cyt b559 reaction center evidently due to formation of easily oxidizable Mn-bicarbonate complexes.

Flash-induced consumption of molecular oxygen on the donor side of photosystem II in Mn-depleted subchloroplast membrane fragments: specific effects of manganese and calcium ions.

It has been shown that removal of manganese from the water-oxidizing complex (WOC) of photosystem II (PSII) leads to flash-induced oxygen consumption (FIOC) which is activated by low concentration of Mn(2+) (Yanykin et al., Biochim Biophys Acta 1797:516-523, 2010). In the present work, we examined the effect of transition and non-transition divalent metal ions on FIOC in Mn-depleted PSII (apo-WOC-PSII) preparations. It was shown that only Mn(2+) ions are able to activate FIOC while other transition metal ions (Fe(2+), V(2+) and Cr(2+)) capable of electron donation to the apo-WOC-PSII suppressed the photoconsumption of O2. Co(2+) ions with a high redox potential (E (0) for Co(2+)/Co(3+) is 1.8 V) showed no effect. Non-transition metal ions Ca(2+) by Mg(2+) did not stimulate FIOC. However, Ca(2+) (in contrast to Mg(2+)) showed an additional activation effect in the presence of exogenic Mn(2+). The Ca(2+) effect depended on the concentration of both Mn(2+) and Ca(2+). The Ca effect was only observed when: (1) the activation of FIOC induced by Mn(2+) did not reach its maximum, (2) the concentration of Ca(2+) did not exceed 40 µM; at higher concentrations Ca(2+) inhibited the Mn(2+)-activated O2 photoconsumption. Replacement of Ca(2+) by Mg(2+) led to a suppression of Mn(2+)-activated O2 photoconsumption; while, addition of Ca(2+) resulted in elimination of the Mg(2+) inhibitory effect and activation of FIOC. Thus, only Mn(2+) and Ca(2+) (which are constituents of the WOC) have specific effects of activation of FIOC in apo-WOC-PSII preparations. Possible reactions involving Mn(2+) and Ca(2+) which could lead to the activation of FIOC in the apo-WOC-PSII are discussed.