Maria Łabanowska

The effects of short-term selenium stress on Polish and Finnish wheat seedlings—EPR, enzymatic and fluorescence studies

Biochemical analyses of antioxidant content were compared with measurements of fluorescence and electron paramagnetic resonance (EPR) to examine the alteration of radicals in wheat seedlings exposed to 2 days of selenium stress. Two genotypes of Polish and one of Finnish wheat, differing in their tolerance to long-term stress treatment, were cultured under hydroponic conditions to achieve the phase of 3-leave seedlings. Afterwards, selenium (sodium selenate, 100 μM concentration) was added to the media. After Se-treatment, all varieties showed an increase in carbohydrates (soluble and starch), ascorbate and glutathione content in comparison to non-stressed plants. These changes were more visible in Finnish wheat. On the basis of lipid peroxidation measurements, Finnish wheat was recognized as the genotype more sensitive to short-term Se-stress than the Polish varieties. The antioxidant enzyme activities (superoxide dismutase, ascorbate peroxidase and glutathione reductase) increased in Polish genotypes, whereas they decreased in Finnish wheat plants cultured on Se media. The action of reactive oxygen species in short-term action of Se stress was confirmed by the reduction of PSII and PSI system activities (measured by fluorescence parameters and EPR, respectively). EPR studies showed changes in redox status (especially connected with Mn(II)/Mn(III), and semiquinone/quinone ratios) in wheat cell after Se treatment. The involvement of the carbohydrate molecules as electron traps in production of long-lived radicals is postulated.

Paramagnetic defects in MoO3—revisited

Detailed interpretation of EPR signals appearing in commercial MoO3 upon reduction invacuo at different temperatures is presented. New O- species in the MoO3 bulk and Mo5+ ions without a molybdenyl bond have been found under such conditions, their intensities depending on temperature and time of reduction. It is argued that formation and stabilization of these unusual species is related to traces of nitrogen impurities. A model of redox processes occurring in MoO3 upon gradual loss of the lattice oxygen and during reconstruction of the MoO3 lattice upon reoxidation of reduced MoO3, involving O- species, as an intermediate stage, is suggested.

Thermal effects on the structure of cereal starches. EPR and Raman spectroscopy studies.

The mechanism of thermal radical generation has been studied in cereal starches containing different amylose contents. Samples of four corn starches and one of wheat has been investigated using electron paramagnetic resonance and Raman spectroscopies. It has been found, that the content of amylose influences the character of thermally created radical species, but in opposite to potato starch, does not affect their amount. During storage of thermally treated starches the evolution of the EPR spectra has been observed. Raman spectra reveal the smaller changes in cereal starches structure occurring upon high temperature than those found for potato starch.

The mechanism of thermal activated radical formation in potato starch studied by electron paramagnetic resonance and Raman spectroscopies

Degradation of starch and the constituent fractions: amylopectin and amylose during thermal treatment in the range 423-503 K was investigated by electron paramagnetic resonance (EPR) and Raman spectroscopy. Degradation process was accompanied by the generation of carbon-centered stable radicals. EPR provided data on the nature and structure of radicals and on their evolution upon thermal treatment, whereas Raman spectroscopy allowed monitoring the changes of bonds in polysaccharides. It was found that amylose was the most susceptible toward high temperatures and the process of radical generation started at lower temperature than in amylopectin and starch, which were more resistant to thermal degradation.

Electron paramagnetic resonance investigation of the paramagnetic centres in polycrystalline MoO3

The defect MoO3 was obtained by thermal decomposition of hexakisammonium heptamolybdate in vacuo at 630 K. Different signals present in the EPR spectrum of reduced MoO3 and those appearing in the course of oxidation, were attributed to Mo5+ ions in various symmetry, situated in different sites of the MoO3 lattice. The signal of Mo3+ ions with effective spin S= 1/2 was observed in the EPR spectrum of both reduced and reoxidized MoO3. A hole centre (Mo—O)5+ was found in reoxidized MoO3. Various methods of stabilization of reduced molybdenum in the MoO3 lattice were postulated.

EPR spectroscopy as a tool for investigation of differences in radical status in wheat plants of various tolerances to osmotic stress induced by NaCl and PEG-treatment.

Two kinds of wheat genotypes with different tolerance to osmotic stress (NaCl and PEG-treatment) were investigated with biochemical analyses, including the measurements of total antioxidant capacity, 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging activity, reducing power and starch content. The results were compared with electron paramagnetic resonance (EPR) data concerning the nature and amounts of stable long lived radicals present in the control and stressed plants. In addition, the changes in manganese content upon stress conditions were monitored. Different mechanisms of protection against PEG stress in sensitive and tolerant wheat genotypes were postulated. In sensitive genotypes, electrons were created in excess in stress conditions, and were stabilized by polysaccharide molecules, whereas in tolerant genotypes, protection by antioxidants dominated. Moreover, the quinone-semiquinone balance shifted towards semiquinone, which became the place of electron trapping. NaCl-treatment yielded significant effects mainly in sensitive genotypes and was connected with the changes of water structure, leading to inactivation of reactive oxygen species by water molecules.

The influence of the starch component on thermal radical generation in flours.

Transition metal ions and radicals in flours of various botanical origins with different content of starch have been studied by EPR before and after thermal treatment. The amounts of metal ions, have been determined by ICP OES. Simulations of EPR spectra have revealed the presence of several types of radicals (carbon-centred, tyrosyl and semiquinone) localized in starch and protein fractions of flours. Thermal treatment of flours significantly increased the amount of radicals with a simultaneous decrease of the signal intensity of transition metal ions. The proposed mechanism of thermal generation of stable organic radicals was associated with the redox processes involving transition metal ions, which facilitated the formation of radicals. The dependence between the way starch is treated and the mechanism of radical formation was also shown.

Effect of mineral elements on physicochemical properties of oxidised starches and generation of free radicals

The objective of this study was to determine the effect of enrichment of oxidised starches with mineral compounds on their physicochemical properties and capability for free radical generation. Potato and spelt wheat starches were oxidised with sodium hypochlorite and, afterwards, modified with ions of potassium, magnesium and iron. The modified starches were analysed for: content of mineral elements, colour parameters (L*a*b*), water binding capacity solubility in water at temperature of 50 and 80 °C, and susceptibility to enzymatic hydrolysis with α-amylase. In addition, thermodynamic characteristics of gelatinisation was determined by differential scanning calorimetry (DSC), and the number and character of thermally generated free radicals was assayed using electron paramagnetic resonance (EPR). Based on the results achieved, it was concluded that the quantity of incorporated minerals and changes in the assayed physicochemical parameters depended not only on the botanical type of starch but also on the type of the incorporated mineral element.

Electron spin resonance investigation of oxygen interaction with V2O5MoO3 catalysts

The changes in reduction degree of V2O5MoO3 catalysts occurring in the course of oxygen adsorption were investigated by electron spin resonance and chemical analysis. Two different types of paramagnetic centers, involving reduced vanadium ions stabilized by oxygen vacancies and substitutional Mo6+ ions, have been found in partially reduced catalysts. The kinetics of oxidation of such catalysts investigated by electron spin resonance revealed a delay in oxidation of the centers stabilized by Mo6+. The role of segregation processes occurring upon redox treatment of the V2O5MoO3 catalysts in determination of the stability of particular centers has been discussed.

Electron paramagnetic resonance (EPR) spectroscopy characterization of wheat grains from plants of different water stress tolerance.

Grains of five genotypes of wheat (four Polish and one Finnish), differing in their tolerance to drought stress were chosen for this investigation. Electron paramagnetic resonance spectroscopy allowed observation of transition metal ions (Mn, Fe, Cu) and different types of stable radicals, including semiquinone centers, present in seed coats, as well as several types of carbohydrate radicals found mainly in the inner parts of grains. The content of paramagnetic metal centers was higher in sensitive genotypes (Radunia, Raweta) than in tolerant ones (Parabola, Nawra), whereas the Finnish genotype (Manu) exhibited intermediate amounts. Similarly, the concentrations of both types of radicals, carbohydrates and semiquinone were significantly higher in the grains originating from more sensitive wheat genotypes. The nature of carbohydrate radicals and their concentrations were confronted with the kinds and amounts of sugars found by the biochemical analyses and microscopy observations. It is suggested that some long lived radicals (semiquinone and starch radicals) occurring in grains could be indicators of stress resistance of wheat plants.