Magdalena Kurdziel

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.

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.

Analysis of odorous compounds at municipal landfill sites.

The aim of this investigation was to determine odorous compounds in the air over the landfill sites in France and Poland. Air samples were collected by passive and dynamic methods of preconcentration analytes and analysed by GC-MS and GC-FID. The coupling µTD-µGC-MS was also used for on-site analysis of odorous compounds. The achieved results indicated that the concentrations of odorants in the air varied and strongly depended on the sampling site. The highest concentrations were observed at the points situated near biogas wells and above the fresh waste layer. The concentrations were influenced by landfill activities such as failures of the landfill gas collection system, heavy truck traffic, machinery operations and compacting fresh waste.

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 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.

Changes of paramagnetic species in cereal grains upon short-term ozone action as a marker of oxidative stress tolerance

The increase of the concentration of ozone in the atmosphere, being the direct source of reactive oxygen species, results in the yield loss of agronomic crops. On the other hand, ozone is also used as a protector against microorganisms, living in plants and present in materials obtained from them, dangerous for human and animal health. In this work it has been studied if ozone in doses similar to those used for removal of microorganisms can have significant influence on the generation of stable organic radicals and changes in the character of transition metal ions and in the antioxidative biochemical parameters of cereal grains. The aim of this work was to find if the response of grains of three cereals (wheat, oat and barley) to ozone depended on their oxidative stress tolerance. The influence of direct short-term ozone application on grains of these cereals, each represented by two genotypes with different oxidative stress tolerance, was studied by biochemical analyses and by electron paramagnetic resonance (EPR) technique. Whole grains as well as their parts: embryo, endosperm and seed coat were subjected to ozone treatment for 30 min. Biochemical investigation of control samples showed that their antioxidant activity increased in order: wheat<oat<barley. EPR method revealed that character and the number of paramagnetic species (transition metal ions: Fe(III), Cu(II), Mn(II) and stable organic radicals) changed upon ozone exposure, depending on the kind of cereal, stress tolerance of particular genotype and the part of grain. The control samples of whole grains and their parts originating from sensitive genotypes contained higher amounts of stable organic radicals (semiquinone, phenoxyl and carbohydrate types) than those from tolerant ones. In embryos of grains from sensitive genotypes their amount increased upon ozone treatment stronger than in embryos from grains of tolerant cultivars. In seed coats and endosperms such relation was not found and the changes in the content of the radicals during ozone application were correlated with the amount of transition metal ions and were more intensive in parts of grains richer in easily oxidized iron species Fe(II), located in inorganic structures. On the contrary, Fe(II) ions situated in embryos were stabilized by organic matrix and did not undergo oxidation by ozone.

Stable radicals and biochemical compounds in embryos and endosperm of wheat grains differentiating sensitive and tolerant genotypes--EPR and Raman studies.

The aim of this study was to uncover the specific species in grains that might differentiate the wheat genotypes according to their tolerance to oxidative stress. Measurements by EPR and Raman spectroscopy techniques were used to examine whole grains and their parts (embryo, endosperm, seed coat) originating from four wheat genotypes with differing tolerance to drought stress. Raman spectra showed that, in spite of the similar amounts of proteins in whole grains from tolerant and sensitive genotypes, in tolerant ones they were accumulated mainly in embryos. Moreover, in embryos from these grains, a higher content of unsaturated fatty acids was observed. Endosperm of grains from the tolerant genotype, richer with starch than that of sensitive one, exhibited higher content of amylopectin. Detailed analysis of EPR signals and simulation procedures of the spectra allowed the estimation of the nature of interactions of Fe(III) and Mn(II) with organic and inorganic structures of grains and the character of organic stable radicals. Three types of these radicals: carbohydrate, semiquinone and phenoxyl, were identified. The amounts of these radicals were higher in grains of sensitive genotypes, mostly because of differences in carbohydrate radical content in endosperm. Taking into account the level of radical concentration and greater capacity for radical formation in grains from plants of lower tolerance to stress, the content of radicals, especially of a carbohydrate nature, was considered as a marker of the plant resistance to stress conditions.