Impact Ionization Induced by Terahertz Radiation in HgTe Quantum Wells of Critical Thickness.

We report on the observation of terahertz (THz) radiation induced band-to-band impact ionization in HgTe quantum well (QW) structures of critical thickness, which are characterized by a nearly linear energy dispersion. The THz electric field drives the carriers initializing electron-hole pair generation. The carrier multiplication is observed for photon energies less than the energy gap under the condition that the product of the radiation angular frequency ω and momentum relaxation time τ l larger than unity. In this case, the charge carriers acquire high energies solely because of collisions in the presence of a high-frequency electric field. The developed microscopic theory shows that the probability of the light-induced impact ionization is proportional to exp ( - E 0 2 / E 2 ) , with the radiation electric field amplitude E and the characteristic field parameter E 0. As observed in experiment, it exhibits a strong frequency dependence for ω τ ≫ 1 characterized by the characteristic field E 0 linearly increasing with the radiation frequency ω.

Valley Subband Splitting in Bilayer Graphene Quantum Point Contacts.

We report a study of one-dimensional subband splitting in a bilayer graphene quantum point contact in which quantized conductance in steps of 4e^{2}/h is clearly defined down to the lowest subband. While our source-drain bias spectroscopy measurements reveal an unconventional confinement, we observe a full lifting of the valley degeneracy at high magnetic fields perpendicular to the bilayer graphene plane for the first two lowest subbands where confinement and Coulomb interactions are the strongest and a peculiar merging or mixing of K and K^{'} valleys from two nonadjacent subbands with indices (N,N+2), which are well described by our semiphenomenological model.

Induction of salt resistance of arabidopsis salicylatedeficient transformants NahG by influence of nitric oxide donor.

The influence of treatment with the donor of nitric oxide sodium nitroprusside (SNP ­ 0,5 mM) on the salt resistance of Arabidopsis plants of wild-type (Col-0) and transformant with the gene of bacterial salicylatehydroxylase (NahG) was compared. The basic resistance against the salt stress (200 mM of NaCl) in transformants NahG was higher. In the conditions of salt stress these plants differed in the higher activity of antioxidant enzymes and the raised content of carbohydrates and anthocyans. The treatment with NO donor increased the salt resistance of plants of both genotypes that expressed in the decrease of growth inhibition, reduction of oxidative damages and preservation of chlorophyll pool in the leaves. After the influence of salt stress the activity of superoxide dismutase and guaiacol peroxidase in treated with SNP wild type plants and transformants was higher, than in the appropriate untreated plants. In the wild type plants, treated with NO donor, the content of proline in leaves after the salt stress was lower, than in untreated. The treatment with SNP of transformants NahG, on the contrary, led to more essential increase of proline content in leaves under the salt stress. The conclusion is made that plants of wild type Col-0 and transformant NahG have differences in the functioning of protective systems under the salt stress, and the induction of protective systems in A. thaliana plants under the influence of nitric oxide can occur without salicylate participation.

[Content of Osmolytes and Flavonoids under Salt Stress in Arabidopsis thaliana Plants Defective in Jasmonate Signaling].

The effects of the salt stress (200 mM NaCl) and exogenous jasmonic acid (JA) on levels of osmolytes and flavonoids in leaves of four-week-old Arabidopsis thaliana L. plants of the wild-type (WT) Columbia-0 (Col-0) and the mutant jin1 (jasmonate insensitive 1) with impaired jasmonate signaling were studied. The increase in proline content caused by the salt stress was higher in the Col-0 plants than in the mutant jin1. This difference was especially marked if the plants had been pretreated with exogenous 0.1 µM JA. The sugar content increased in response to the salt stress in the JA-treated WT plants but decreased in the jin1 mutant. Leaf treatment with JA of the WT plants but not mutant defective in jasmonate signaling also enhanced the levels of anthocyanins and flavonoids absorbed in UV-B range. The presence of JA increased salinity resistance of the Col-0 plants, since the accumulation of lipid peroxidation products and growth inhibition caused by NaCl were less pronounced. Under salt stress, JA almost did not render a positive effect on the jin1 plants. It is concluded that the protein JIN1/MYC2 is involved in control of protective systems under salt stress.

[Salt Stress Response in Arabidopsis thaliana Plants with Defective Jasmonate Signaling].

The effects of exogenous jasmonic acid (JA) on antioxidant enzymes in four-week-old leaves of wild-type Arabidopsis thaliana L. (Columbia-0) and jin1 (jasmonate insensitive 1) mutant plants with defective jasmonate signaling were investigated under normal conditions and under salt stress (200 mM NaCl, 24 h). The wild-type plants responded to JA by an increase in the activities of Cu/Zn superoxide dismutase, catalase, and guaiacol peroxidase, while there was no change in the case of the mutant plants. In response to the salt stress of both the wild-type and mutant genotypes, the activities of superoxide dismutase, catalase, and guaiacol peroxidase were unchanged, decreased, and increased, respectively. The JA-treated wild type plants showed the highest activity of all three enzymes as compared with the mutant plants. Salinity caused a decrease in chlorophyll content in the wild-type and jin 1 plants. Preliminary JA treatment of the Col-0 plants resulted in a normal content of photosynthetic pigments after the salt stress, while the positive JA effect was insignificant in the jin 1 mutants. It was concluded that the MYC2/JIN 1 protein is involved in the JA signal transduction and plant adaptation to salt stress.

Magnetoresistance in two-component systems.

Two-component systems with equal concentrations of electrons and holes exhibit nonsaturating, linear magnetoresistance in classically strong magnetic fields. The effect is predicted to occur in finite-size samples at charge neutrality due to recombination. The phenomenon originates in the excess quasiparticle density developing near the edges of the sample due to the compensated Hall effect. The size of the boundary region is of the order of the electron-hole recombination length that is inversely proportional to the magnetic field. In narrow samples and at strong enough magnetic fields, the boundary region dominates over the bulk leading to linear magnetoresistance. Our results are relevant for two-and three-dimensional semimetals and narrow band semiconductors including most of the topological insulators.

[Possible pathways of heat resistance induction in plant cells by exogenous nitrogen oxide].

The mechanisms of influence of exogenous nitrogen oxide (NO) on heat resistance of wheat coleoptiles have been studied. The treatment of plant cells with nitrogen oxide donor (sodium nitroprusside) resulted in the increase of superoxide anion-radical (O2*-) generation already after 10 minutes. The inhibitor of protein biosynthesis cycloheximide did not inhibit the O2*- generation by coleoptiles caused with the NO donor whereas the inhibitor of phosphatidic acid formation (butanol-1) partially inhibited it. The treatment of coleoptiles with the calcium ionophore (A23187) or activator of inositol cycle (inositol) compensated the suppression of butanol-1 effect on NO-dependent O2*- formation. Butanol-1 has also leveled the induction of coleoptiles heat resistance caused by the NO donor, whereas calcium ionophore and inositol almost completely removed the butanol-1 effect. The possible mechanisms of participation of reactive oxygen species, phosphatidic acid and calcium ions in the realization of NO physiological effects are discussed.

Aharonov-Bohm conductance through a single-channel quantum ring: persistent-current blockade and zero-mode dephasing.

We study the effect of electron-electron interaction on transport through a tunnel-coupled single-channel ring. We find that the conductance as a function of magnetic flux shows a series of interaction-induced resonances that survive thermal averaging. The period of the series is given by the interaction strength α. The physics behind this behavior is the blocking of the tunneling current by the circular current. The main mechanism of dephasing is due to circular-current fluctuations. The dephasing rate is proportional to the tunneling rate and does not depend on α.

Tunneling into a Luttinger liquid revisited.

We study how electron-electron interactions renormalize tunneling into a Luttinger liquid beyond the lowest order of perturbation in the tunneling amplitude. We find that the conventional fixed point has a finite basin of attraction only in the point contact model, but a finite size of the contact makes it generically unstable to the tunneling-induced breakup of the liquid into two independent parts. In the course of renormalization to the nonperturbative-in-tunneling fixed point, the tunneling conductance may show a nonmonotonic behavior with temperature or bias voltage.

[Callose accumulation during treatment of tomato (Lycopersicon esculentum L.) cells with biotic elicitors].

Time-course of induced accumulation of callose in tomato cells has been studied. Localization of callose in L. esculenthum cells was investigated by fluorescent microscopy technique, and the optimal time for its determination was found. Callose accumulation in tomato cells treated with different biotic elicitors was determined. Nonlinear dependence between callose accumulation and concentration of chitin oligomers (with 3-5 N-acetylglucosamine fragments) was established. Increasing of callose accumulation in tomato cells was proportional to the increase of concentration ofchitin dimer and chitosan in the culture medium.

[Mechanisms of action of plant resistance inductor beta-aminobutyric acid in Allium cepa].

The effects of beta-aminobutiric acid as an inductor of plant resistance was studied. The influence of BABA pretreatment on A. cepa plants of three different pathogen-resistant varieties was investigated by fluorescence microscopic methods. It was determined that BABA is able to prime the plant callose accumulation.

[The induced increase of chitinase activity in tomato (Lycopersicon esculentum L) cells].

The levels of chitinase activity induced with elicitors in tomato cells have been detected. It was shown that enzymatic activity depended on degree of polymerization and concentration of biotic elicitors.

[Signal role of nitric oxide in plants]. / Signal'naia rol' oksida azota u rastenii.

Discovery of nitric oxide (NO*) as a key endogenous molecule, which regulates metabolism among very distantly related organisms, stimulated intensive research related to its multiple functions in plants. NO* exerts its cellular effects as toxic agent, metabolism regulator, second messenger during elicitation of different defense responses. It can induce various processes in plants, including programmed cell death, stomatal closure, seed germination and root development. Currently, elucidation of NO* signaling role in regulation of cellular responses is a "hot spot" of modern cell biology.

Induction of systemic resistance in plants.

When a pathogen is perceived by a host plant, a series of defense responses can be activated. One of these are "local" defenses that occur rapidly at the site of pathogen invasion. Another are "systemic" defenses that are induced in uninoculated parts of the plant. Recently, molecular genetic studies have revealed genes that are signaling components of systemic resistance pathways. Cloning of these genes and characterization of the function of their proteins is now providing insights to processes regulating plant defense against pathogens. Evidence that "systemic" defenses are important for resistance is that when the way is blocked in transgenic plants or in mutants, the plant's defense is compromised. When the pathway is stimulated by exogenous compounds or in mutants, the host resistance is strengthened. A detailed understanding of this pathway is important for both practical and theoretical reasons.

[Signal systems of plant immunity]. / Signal'nye sistemy immuniteta rastenii.

Plants can recognise the penetrating pathogen and respond to the attack with an array of defense reactions. Signal transduction from receptor in plasma membrane to genome is necessary to activate these reactions. Plant cell signaling systems which take part in signal transduction were discovered and identified recently. The obtained results suggest that plant cells have complex and well coordinated signal network which regulates their immune potential.

[Effects of chronic irradiation on the adaptive potential of plants]. / Vliianie khronicheskogo oblucheniia na adaptivnyi potentsial rastenii.

The content of anthocianins was determined in Oenothera biennis plants, grown from seeds, picked on the plots with different levels of radionuclide contamination in the 30-km Chernobyl zone. It was shown that the content of anthocianins was higher in plants from Yanov area (20-40 mR/h) than in plants from Chernobyl area (0.04 mR/h). An acute gamma-irradiation of seeds with a dose of 5-100 Gy or UV-irradiation of plants resulted in increasing of anthocianin content which was higher in plants grown from the seeds picked on plots with a low level of radionuclide contamination. The data obtained suggest that chronic irradiation of O. biennis populations induces accumulation of anthocianins. Apparently the adaptivity potential has been more completely realised in plants on the plots with a higher level of radionuclide contamination. The populations which were formed in the absence or at the low level of radionuclide contamination, on the contrary, have a significant adaptivity potential and, accordingly, higher radioresistance.

[Induction of active forms of oxygen by biotic elicitors in tomato cell cultures]. / Induktsiia aktivnykh form kisloroda bioticheskimi élisitorami v kul'ture kletok tomatov.

The elicitor-induced generation of two oxygen species in tomato cell culture as well as their involvement into hypersensitive reaction was investigated. Generation of superoxide O2.- was measured by a lucigenin-related chemiluminescence. Accumulation of hydrogen peroxide H2O2 was measured by a fluorescent probe pyranin. Xylanase and chitosan were used as biotic elicitors with different mode of action. It was found that both O2.- and H2O2 had been accumulated in elicitor-treated tomato cells. The results obtained show that reactive oxidants are important signal transduction elements for activation of hypersensitive response in tomato cells.