Mid-holocene Brown Bear (Ursus arctos) from the Bolshoy Lyakhovsky Island (New Siberian Islands).

A morphological description is provided for a unique find of a frozen mummified subfossil brown bear (Ursus arctos L., 1758), found for the first time ever. The find is a well-preserved bear carcass of approximately 3500 years in age. Results of computed tomography and DNA testing are discussed.

The Interaction of Water-Soluble Nitroxide Radicals with Photosystem II.

In this work, we investigated the redox transients of a number of water-soluble spin labels upon their interactions with Photosystem II (PS II) core complexes isolated from spinach leaves. We have found that the reactivity of nitroxide radicals, determined by the rate of their reduction upon illumination of PS II, depends on the chemical structure of radicals and the capability of their coming close to low-potential redox centers of photoactive PS II complexes. An enhanced capability of nitroxide radicals to accept electrons from PS II correlates with their chemical structure. Nitroxide radicals NTI (2,2,5,5-tetramethyl-4-nitromethylene-3-imidazolidine-N-oxyl) and Tacet (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl-acetate), containing polar groups, appear to be most efficient acceptors of electrons donated by PS II compared to neutral (TEMPOL, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl) or positively charged (Tamine, 4-amino-2,2,6,6-tetramethylpiperidine-l-oxyl) spin labels. We assume that enhanced reactivities of polar nitroxide radicals, NTI and Tacet, are determined (1) by their relatively high redox potentials, providing the possibility to accept electrons from PS II, and (2) by their affinities to the closest binding sites on the surface of PS II in the vicinity of the primary plastoquinone acceptor PQA (12-14 Å) or/and in the intraprotein cavity for the secondary plastoquinone PQB (~ 22 Å).

Electron Transfer through the Acceptor Side of Photosystem I: Interaction with Exogenous Acceptors and Molecular Oxygen.

This review considers the state-of-the-art on mechanisms and alternative pathways of electron transfer in photosynthetic electron transport chains of chloroplasts and cyanobacteria. The mechanisms of electron transport control between photosystems (PS) I and II and the Calvin-Benson cycle are considered. The redistribution of electron fluxes between the noncyclic, cyclic, and pseudocyclic pathways plays an important role in the regulation of photosynthesis. Mathematical modeling of light-induced electron transport processes is considered. Particular attention is given to the electron transfer reactions on the acceptor side of PS I and to interactions of PS I with exogenous acceptors, including molecular oxygen. A kinetic model of PS I and its interaction with exogenous electron acceptors has been developed. This model is based on experimental kinetics of charge recombination in isolated PS I. Kinetic and thermodynamic parameters of the electron transfer reactions in PS I are scrutinized. The free energies of electron transfer between quinone acceptors A1A/A1B in the symmetric redox cofactor branches of PS I and iron-sulfur clusters FX, FA, and FB have been estimated. The second-order rate constants of electron transfer from PS I to external acceptors have been determined. The data suggest that byproduct formation of superoxide radical in PS I due to the reduction of molecular oxygen in the A1 site (Mehler reaction) can exceed 0.3% of the total electron flux in PS I.

Chlorophyll fluorescence induction, chlorophyll content, and chromaticity characteristics of leaves as indicators of photosynthetic apparatus senescence in arboreous plants.

Parameters of chlorophyll fluorescence induction (CFI) are widely used for assessment of the physiological state of higher plant leaves in biochemical, physiological, and ecological studies and in agricultural applications. In this work we have analyzed data on variability of some CFI parameters - ΦPSII(max) = Fv/Fm (relative value of variable fluorescence), qNPQ (non-photochemical quenching coefficient), RFd ("vitality index") - in autumnal leaves of ten arboreous plant species of the temperate climatic zone. The correlation between the chlorophyll content in the leaves and fluorescence parameters characterizing photosynthetic activity is shown for two representative species, the small-leaved linden Tilia cordata and the rowan tree Sorbus aucuparia. During the period of mass yellowing of the leaves, the ΦPSII(max) value can be used as an adequate characteristic of their photochemical activity, while in summer the qNPQ or RFd values are more informative. We have established a correlation between the ΦPSII(max) value, which characterizes the maximal photochemical activity of the photosystem II, and "chromaticity coordinates" of a leaf characterizing its color features. The chromaticity coordinates determined from the optical reflection spectra of the leaves serve as a quantitative measure of their hues, and this creates certain prerequisites for a visual expert assessment of the physiological state of the leaves.

[Biophysical methods of ecological monitoring. Photosynthetic characteristics of tree plants growing in Moscow city].

In this work, we studied an influence of ecological factors (a distance from the highway) on photosynthetic characteristics of leaves of four species of tree plants growing in Moscow city. Photosynthetic activity of leaves was assayed by instrumental methods of probing the functional state of photosynthetic apparatus, using electron paramagnetic resonance method for measuring the kinetics of photooxidation of P700 centers, thermoluminescence, and slow induction of chlorophyll fluorescence. It has been shown that kinetic parameters of the induction curves, as measured from the kinetics of photooxidation of P700 and slow induction of chlorophyll fluorescence in dark-adapted leaves, are sensible to variations of plant growing conditions. These parameters can be used as informative characteristics for ecological monitoring of the environment.

[Luminescence characteristics of strawberry leaves in early stages of their injury by arachnoidal mite].

In this work, we have investigated how the luminescence characteristics and a total content of antioxidants in leaves of strawberry (Fragaria x ananassa Duch.) change after infestation of plants by spider mite (Tetranychus atlanticus McGregor). At the earlier stage of plant injury, the chlorophyll concentration remained unchanged. However, the total amount of antioxidants decreased and the intensity of high-temperature band (60 divided by 100 degrees C) of thermoluminescence increased, indicating a degradation of membrane lipids caused by oxidative stress. In infected leaves, the light-induced rise of non-photochemical quenching of chlorophyll fluorescence was slower, while the relaxation of non-photochemical quenching in the dark was faster than in control samples of leaves. These data might indicate that the thylakoid membranes in infested leaves were more permeable for ions than in control leaves.

[Electron transport and transmembrane proton transfer in photosynthetic systems of oxygenic type in silico].

In this work, using a mathematical model of light-induced stages of photosynthesis, taking into account the key stages of pH-dependent regulation on the acceptor and donor sides of PS1, we analyzed electron and proton transport in chloroplasts of higher plants and cyanobacterial cells. A comparison of computer simulation results with experimental data showed that our model adequately described a complex non-monotonous kinetics of the light-induced redox transients of P700. Effects of atmospheric gases (CO2 and O2) on the kinetics of photooxidation of P700 and generation of the transmembrane pH difference were studied. We also analyzed how cyclic electron transport influenced the kinetics of electron transfer, the intrathylakoid pH, and ATP production. Within the framework of our model, we described the time-courses of electron flow through PS2 and distribution of electron fluxes on the acceptor side of PS1 in chloroplasts of higher plants and in cyanobacterial cells. It was demonstrated that contributions of cyclic electron transport and electron flow to O2 (the Mehler reaction) were significant during the initial phase of the induction period, but diminished upon the activation of the Calvin-Benson cycle.

Energetic and regulatory role of proton potential in chloroplasts.

The review focuses on the energetic and regulatory role of proton potential in the activity of chloroplasts, the light energy-converting organelles of plant cells. Mechanisms of generation of the transmembrane difference of electrochemical potentials of hydrogen ions (Δµ(~)(H+)) in the chloroplast thylakoid membranes are considered. Methods for measuring the intrathylakoid pH in chloroplasts are described. It is shown that under conditions of phosphorylation in chloroplasts, the pH of the intrathylakoid space decreases moderately (pH(in) ≥ 6.0-6.2, at the stroma pH(out) ≈ 7.8-8.0), with a corresponding concentration component of Δµ(~)(H+) equal to ΔpH ≤ 1.6-2.0. On analyzing the energy and structural features of ATP synthase of chloroplasts, we conclude that the energy stored as the concentration component of the proton potential ΔpH is sufficient to sustain ATP synthesis. The mechanisms of pH-dependent regulation of electron transport in chloroplasts (photosynthetic control of electron transport, enhancement of non-photochemical quenching of chlorophyll excitation in the light-harvesting antenna, light-induced activation of the Calvin-Benson cycle reactions, activation of ATP synthase) are considered briefly.

Arthropod symbiotes of Laonastes aenigmamus (Rodentia:Diatomyidae).

Arthropod symbiotes of the Laotian rock-rat, Laonastes aenigmamus (Rodentia:Diatomyidae), from Laos are examined. This host is a member of Diatomyidae previously thought to have gone extinct >10 million yr ago. Permanent symbiotes are represented by 2 species, a new species of sucking louse, Polyplax sp., near rhizomydis (Phthiraptera:Polyplacidae), and a new species of fur mite, Afrolistrophorus sp., near maculatus (Acariformes:Listrophoridae). The temporary parasites are represented by 18 species, i.e., 1 mesostigmatan species, i.e., a new species of Androlaelaps near casalis (Parasitiformes:Laelapidae); immature stages of 2 tick species, Ixodes granulatus and Haemaphysalis sp. (Parasitiformes:Ixodidae); and a rich fauna of chiggers (Acariformes:Trombiculidae) comprising 8 genera and 15 species. It is hypothesized that this host completely lost its initial fauna of ectosymbiotes and that ancestors of the recorded symbiotes switched to this host from rodents of the superfamily Muroidea.

Effects of light environment on the induction of chlorophyll fluorescence in leaves: a comparative study of Tradescantia species of different ecotypes.

In this work, using a PAM-fluorimetry technique, we have compared effects of plant adaptation to the light or dark conditions on the kinetics of chlorophyll a fluorescence yield in Tradecantia leaves of several species (Tradescantia albiflora, Tradescantia fluminensis, Tradescantia navicularis, and Tradescantia sillamontana), which represent plants of different ecotypes. Two fluorescence parameters were used to assess photosynthetic performance in vivo: non-photochemical quenching (NPQ) of chlorophyll fluorescence (q(NPQ)) determined by energy losses in the light-harvesting antenna of photosystem 2 (PS2), and PS2 operating efficiency (Φ(PSII)). Comparative study of light-induced changes in q(NPQ) and Φ(PSII) has demonstrated that shade-tolerant Tradecantia species (T. albiflora Kunth, T. fluminensis Vell.) reveal higher capacities for NPQ and demonstrate slower transitions between the 'light-adapted' and 'dark-adapted' states than succulent species T. navicularis and T. sillamontana, which are typical habitats of semi-deserts. We analyze the photosynthetic performance of Tradescantia species in the context of their adaptabilities to variable environment conditions. The ability of shade-tolerant plants to retain a relatively long-term (∼40-60 min) 'memory' for illumination history may be associated with the regulatory mechanisms that provide the flexibility of photosynthetic apparatus in response to fluctuations of light intensity.

[pH-dependent regulation of electron transport in chloroplasts. Computer simulation investigation].

A mathematical model for the description of the key stages of photosynthetic electron transport and transmembrane proton transfer in chloroplasts is presented. Numerical modeling of electron and proton transport with due regard for regulatory processes on the donor and acceptor sites of photosystem I (PS I) was performed. The influence of pH-dependent activation of the Calvin cycle enzymes and energy dissipation in PS II (nonphotochemical quenching of chlorophyll fluorescence) on the kinetics of light-reduced redox transients of P700, plastoquinone and NADPH, as well as intrathylakoid pH(in), and ATP was studied. It was demonstrated that pH-dependent regulatory processes influence the distribution of electron fluxes on the acceptor site of PS I and the total rate of electron flow between PS II and PS I. The light-induced activation of the Calvin cycle enzymes leads to a significant acceleration of the electron flow to NADP+ and the reduction of the electron flow from PS 1 to molecular oxygen.

[Slow fluorescence induction and CO2-exchange in bean leaves treated with Reynoutria sachalinensis extract].

It has been shown that the treatment of bean seedlings with a water extract of Reynoutria sachalinensis increases visible photosynthesis and the activity of dark respiration of plants. The increase in CO2-uptake under relatively high light illumination (10000 1x) correlates with an increase in the fluorescence parameter (F(M) - F(T))/F(T).

[F1-ATPase as a self-excited oscillatory system].

A mathematical model for F1-type ATPase is presented, which shows that this enzyme can operate as a self-excited oscillatory system.