Yu. V. Ivanov

Role of antioxidant systems in wild plant adaptation to salt stress

Wild plants differing in the strategies of adaptation to salinity were grown for six weeks in the phytotron and then subjected to salt stress (100 mM NaCl, 24 h). The activities of principal antioxidant enzymes and the accumulation of sodium ions and proline were studied. Independently of the level of constitutive salt tolerance, plants of all species tested accumulated sodium ions under salinity conditions but differed in their capability of stress-dependent proline accumulation and superoxide dismutase (SOD) and guaiacol-dependent peroxidase activities. Proline-accumulating species were found among both halophytes (Artemisia lerchiana and Thellungiella halophila) and glycophytes (Plantago major and Mycelis muralis). The high activities of ionically-bound and covalently bound peroxidases were characteristic of Th. halophila plants. High constitutive and stress-induced SOD activities were, as a rule, characteristic of glycophytes with the low constitutive proline level: Geum urbanum and Thalictrum aquilegifolium. Thus, a negative correlation was found between proline content and SOD activity in wild species tested; it was especially bright in the halophyte Th. halophila and glycophyte G. urbanum. An extremely high constitutive and stress-induced levels of proline and peroxidase activity in Th. halophila maybe compensate SOD low activity in this plant, and this contributed substantially into its salt resistance. Thus, monitoring of stress-dependent activities of some antioxidant enzymes and proline accumulation in wild plant species allowed a supposition of reciprocal interrelations between SOD activity and proline accumulation. It was also established that the high SOD activity is not obligatory trait of species salt tolerance. Moreover, plants with the high activity of peroxidase and active proline accumulation could acclimate to salts stress (100 mM NaCl, 24 h) independently of SOD activity.

Functioning of Defense Systems in Halophytes and Glycophytes under Progressing Salinity

Six-week-old Plantago major L. and Thellungiella halophila Mey. plants were subjected to progressing salinity by a daily increase in the NaCl concentration by 100 mM until the final concentration of 400 mM. A dynamics of stress-dependent accumulation of Na+ and Cl− ions, proline, and free polyamines and also activities of antioxidant enzymes, superoxide oxidase (SOD) and free, ion-bound, and covalently bound guaiacol-dependent peroxidases was studied. We also examined the intensity of gene expression encoding enzymes of proline metabolism and polyamine biosynthesis. It was shown that the high salt-resistance of the halophyte T. halophila was determined by plant capability of ion accumulation and stress-dependent proline accumulation. An important role in the maintenance of this plant homeostasis under salinity plays a high constitutive levels of activities of three types of peroxidases tested and also of proline manifesting a polyfunctional protective action. In contrast, P. major plants characterized by a lower tolerance to salt excess did not display a high constitutive level of proline or the activity of guaiacol-dependent peroxidases; they also were not capable of stress-induced accumulation of compatible osmolytes and did not accumulate the salt. However, this glycophyte contained relatively much spermidine and active SOD, which provided for a decrease in the damaging effects of reactive oxygen species under salt shock. In both plant species, it was established that salinity changed the intracellular content of polyamines, which was not dependent on the activity of gene transcription encoding the enzymes of their biosynthesis. The results obtained support a hypothesis that halophytes and glycophytes have some common mechanisms of tolerance to salinity, but the control of these mechanisms differs substantially.

Scots pine as a model plant for studying the mechanisms of conifers adaptation to heavy metal action: 1. Effects of continuous zinc presence on morphometric and physiological characteristics of developing pine seedlings

Effects of zinc (50–150 μM ZnSO4) on seed germinability, morphometric and physiological characteristics of Scots pine (Pinus sylvestris L.) seedlings during first 6 weeks of their development were studied. Scots pine turned out to be rather sensitive to elevated zinc concentrations. This was manifested in reduced seed germinability, root system growth retardation and suppression of its development (primarily, reduction in the size of the zone of secondary root formation, their number, and total length), a disturbance in the dynamics of biomass accumulation by various organs, primarily true needles, and also the content of main photosynthetic pigments. A specificity of zinc accumulation in seedling organs was established; it depended on the degree of root system development. A competition between cotyledons and needles for essential elements was observed. It was concluded that Scots pine high sensitivity to relatively low zinc concentrations (50–150 μM) makes it a more convenient model than currently used model plants (Arabidopsis thaliana L., Mesembryanthemum crystallinum L., Brassica napus L., and others) for studying physiological and molecular mechanisms of conifers adaptation to heavy metals and also for predictions of possible ecological consequences of environment pollution with zinc for tree phytocenoses.

Inducible and constitutive mechanisms of salt stress resistance in Geum urbanum L.

The avens (Geum urbanum L.) seedlings were grown for 6 weeks until the expansion of five to six leaves and then exposed to salinity shock (300 mM NaCl in the nutrient medium) or to a gradual (within 4 days) increase in NaCl concentration from 100 to 400 mM. The dynamics of stress-dependent accumulation of Na+, Cl−, proline, and polyamines in leaves and roots was measured, together with activities of antioxidant enzymes, namely, superoxide dismutase (SOD) and guaiacol-dependent peroxidase occurring in soluble, ionically bound, and covalently bound forms. It is shown that avens plants can adapt to gradual salinization by mobilizing stressinducible protective mechanisms (accumulation of proline and spermine) and by activating constitutive enzyme systems (SOD and peroxidase).

Application of fluctuating asymmetry indexes of silver birch leaves for diagnostics of plant communities under technogenic pollution

The prospects for applying the fluctuating asymmetry (FA) of silver birch (Betula pendula Roth) leaves for diagnosis of plant community conditions in technogenically polluted environments are considered with an example of the effect of heavy metals and chronic ionizing radiation. An increase in the minimum sample size to 150–180 leaves and measurements of morphometric traits with an improved accuracy of 0.06–0.07 mm made it possible to overcome the influence of sample size on FA parameters. The excess content of nickel (18.5 times with respect to the background level), lead (16.0 times), manganese (5.8 times), and copper (3.0 times) in birch leaves was accompanied by the increase in multivariate FA index by 20.0%. The chronic exposure to ionizing radiation (at absorbed dose rate on the soil surface of 4.74 µGy/h) elevated the multi-variate FA index of leaves by 29.8% and the content of chlorophylls a and b in leaves by 50.3 and 82.9%, respectively. It was found that the most informative morphometric trait for analysis of birch leaf FA is the distance between the bases of the first and second lateral veins; its FA index rose to 40.4% under the influence of heavy metals and to 53.6% under exposure to chronic ionizing radiation. Thus, FA can be regarded as a sensitive biomarker for detecting early negative responses of forest ecosystems to technogenic pollution.

Photolysis of 7,8-digermabicyclo[2.2.2]octadiene. The investigation of the elementary stages by means of 1H CIDNP and laser pulse photolysis

Photolysis of 7,8-digermabicyclo[2.2.2]octadiene (I) was studied by means of 1H-CIDNP and laser pulse photolysis techniques. It was found that photodecomposition of I occurs via germanium-centered 1,6-biradical species. 1,4-Diphenylnaphthalene and tetramethyldigermene are the primary products of the photolytic reaction.

Regulation of gene expression governing proline metabolism in Thellungiella salsuginea by NaCl and paraquat

Differential expression of the proline metabolism genes in Thellungiella salsuginea (Pall) E. Schulz was investigated under salinity (100 and 300 mM NaCl), upon the effect of paraquat (0.1 μM), and at their joint action. It was shown that, depending on the intensity of stress factor, expression of the P5CS1 gene was induced in the leaves (at 100 mM NaCl) or roots (at 300 mM NaCl). When the plants on control medium were treated with paraquat, the proline content changed only in the leaves. Time course of proline content in the leaves complied with the dynamic of P5CS1 gene expression, while expression of PDH gene essentially did not change. When the plants, which experienced salt stress, were treated with paraquat, the content of proline and the P5CS1 mRNA level increased even more. The obtained results suggest a complicated nature of signaling between the organs of the halophyte Th. salsuginea causing expression of the proline biosynthesis genes in the leaves and roots under the effect of salinity, paraquat, or upon their joint action. The proline catabolism in these plants was maintained essentially unchanged, which is probably related to the participation of proline and/or the products of its degradation in the pathways of other metabolite biosynthesis. We suggested that proline took part in ROS scavenging process and proline level was under strong control in Th. salsuginea.

Scots pine as a model plant for studying the mechanisms of conifers adaptation to heavy metal action: 2. Functioning of antioxidant enzymes in pine seedlings under chronic zinc action

Functioning of antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APO), and guaiacol peroxidases (GPO)) and low-molecular organic ROS scavengers (proline and phenolic compounds) in various organs (roots, cotyledons, stem, and needle) of 6-week-old seedlings of pine (Pinus sylvestris L.) developing in the chronic presence of ZnSO4 (50, 100, and 150 μM). Pine seedlings were grown in water culture in the climate-controlled chamber at an irradiance of 37.6 W/m2 with a 16-h photoperiod, an air temperature of 23 ± 1/15 ± 1°C (day/night), and a relative humidity of 55/70% (day/night). Endogenous Zn content was a key factor determining SOD activity decomposing superoxide into H2O2 and O2. Hydrogen peroxide produced is efficiently destroyed by CAT and also by APO and GPO. At the same time, the content of proline increased (especially at 150 μM ZnSO4), but the content of phenolic compounds remained unchanged. All these processes help to maintain stable intracellular levels of O2⊙− and H2O2 at elevated zinc concentrations and to prevent generation of hydroxyl radical and development of oxidative stress.

Paramagnetic intermediates in the photolysis of 7-silanorbornadiene studied by means of spin chemistry method

Abstract The influence of an external magnetic field on the yield of photo-decomposition products of 7,7′-dimethyl-7-silanorbornadiene derivative has been detected in laser pulse photolysis experiments. The observations of magnetic field effects alterations in the presence of scavengers, O 2 and PPh 3 , in combination with 1 H-CIDNP data form the basis for the identification of the structure of paramagnetic intermediates involved in the process. It has been shown that magnetic field effects originate in biradical intermediates. These species result from both endocyclic SiC bond cleavage in the initial compound and the reaction of dimethylsilylene (in a singlet or a triplet excited state) with starting 7-silanorbornadiene. To explain the influence of O 2 upon the magnetic field effects, the reversible formation of oxygen complex with biradical species has been suggested.

Spectroscopy and kinetics of dithiophosphinate radicals coordinated with dithiophosphinate Ni(II) complex

Abstract The laser flash photolysis was used to study the mechanism of photochromic transformations for solutions of phosphinate disulfide ((S2P(i-Bu)2)2≡(S2PR2)2) and Ni(S2P(i-Bu)2)2(Ni(S2PR2)2) complex in acetonitrile. Under the excitation of an XeCl excimer laser (308 nm), this system manifests transient absorption in the visible and UV ranges which vanishes over a millisecond time domain. The cycle of phototransformations can be repeated without degradation of the optical spectrum of the solution. The process is initiated by photodissociation of a disulfide molecule into two S-radicals ( S 2 P ( i-Bu ) 2 ≡ S 2 PR 2 ) . The radical with a constant of 2.5×10 9 M −1 s −1 enters the coordination sphere of Ni(S2PR2)2 complex to form the radical complex (R2PS2 )Ni(S2PR2)2. When analyzing the kinetics of changes in the optical density of transient absorption, it is assumed that coordination of the second radical with a constant of 1.5×10 10 M −1 s −1 results in the formation of the secondary or biradical complex (R2PS2 )2Ni(S2PR2)2. The radical complexes dissociate with a radical escaping from the coordination sphere with rate constants equal to 7.5×10 3 s −1 and 7×10 2 s −1 for mono- and biradical particles, respectively. As a result, the system regains its initial state due to recombination of S 2 PR 2 radicals into initial disulfide.