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

Enhancing salinity tolerance in cucumber through Selenium biofortification and grafting

BACKGROUND

Salinity stress is a major limiting factor for plant growth, particularly in arid and semi-arid environments. To mitigate the detrimental effects of salinity stress on vegetable production, selenium (Se) biofortification and grafting onto tolerant rootstocks have emerged as effective and sustainable cultivation practices. This study aimed to investigate the combined effects of Se biofortification and grafting onto tolerant rootstock on the yield of cucumber grown under salinity stress greenhouse conditions. The experiment followed a completely randomized factorial design with three factors: salinity level (0, 50, and 100 mM of NaCl), foliar Se application (0, 5, and 10 mg L-1 of sodium selenate) and grafting (grafted and non-grafted plants) using pumpkin (Cucurbita maxima) as the rootstock. Each treatment was triplicated.

RESULTS

The results of this study showed that Se biofortification and grafting significantly enhanced salinity tolerance in grafted cucumbers, leading to increased yield and growth. Moreover, under salinity stress conditions, Se-Biofortified plants exhibited increased leaf relative water content (RWC), proline, total soluble sugars, protein, phenol, flavonoids, and antioxidant enzymes. These findings indicate that Se contributes to the stabilization of cucumber cell membrane and the reduction of ion leakage by promoting the synthesis of protective compounds and enhancing antioxidant enzyme activity. Moreover, grafting onto pumpkin resulted in increased salinity tolerance of cucumber through reduced Na uptake and translocation to the scion.

CONCLUSION

In conclusion, the results highlight the effectiveness of Se biofortification and grafting onto pumpkin in improving cucumber salinity tolerance. A sodium selenate concentration of 10 mg L-1 is suggested to enhance the salinity tolerance of grafted cucumbers. These findings provide valuable insights for the development of sustainable cultivation practices to mitigate the adverse impact of salinity stress on cucumber production in challenging environments.

Lignin and organic free radicals in maize (Zea mays L.) seeds in response to aflatoxin B1 contamination: an optical and EPR spectroscopic study

BACKGROUND

Aflatoxin B₁ (AFB₁ ) is the most dangerous of the mycotoxins that contaminate cereal seeds naturally. A stress lignin formation is linked with the accumulation of reactive oxygen species causing a change in the redox status and formation of stable organic radicals, constituting the first layer of defense. The relationship between AFB₁ and changes in lignin organic free radicals in seeds is not known, nor is the part of the seed that is more targeted. Using optical and electron paramagnetic resonance spectroscopy, we investigated AFB₁ -induced changes in lignin and organic free radicals in seeds, and whether the inner and outer seed fractions differ in response to increasing AFB₁ .

RESULTS

Different changes in the content of lignin and free radicals with increasing AFB₁ concentrations were observed in the two seed fractions. There was a significant positive linear correlation (R = 0.9923, P = 0.00005) between lignin content and AFB₁ concentration in the outer fraction, and no correlation between the lignin content and the AFB₁ concentration in the inner fraction. We found a positive correlation between the area of the green spectral emission component (C4) and the AFB₁ concentration in the outer fraction.

CONCLUSIONS

To the best of our knowledge, the results showed, for the first time, that maize seed fractions respond differently to aflatoxin with regard to their lignin and organic free radical content. Lignin content and (C4) area may be reliable indicators for the screening of lignin changes against AFB₁ content in the seeds, and thus for seed protection capacity. © 2021 Society of Chemical Industry.

Protective responses of tolerant and sensitive wheat seedlings to systemic and local zearalenone application - Electron paramagnetic resonance studies

BACKGROUND

Mycotoxins are among the environmental stressors whose oxidative action is currently widely studied. The aim of this paper was to investigate the response of seedling leaves to zearalenone (ZEA) applied to the leaves (directly) and to the grains (indirectly) in tolerant and sensitive wheat cultivars.

RESULTS

Biochemical analyses of antioxidant activity were performed for chloroplasts and showed a similar decrease in this activity irrespective of plant sensitivity and the way of ZEA application. On the other hand, higher amounts of superoxide radical (microscopic observations) were generated in the leaves of plants grown from the grains incubated in ZEA solution and in the sensitive cultivar. Electron paramagnetic resonance (EPR) studies showed that upon ZEA treatment greater numbers of Mn - aqua complexes were formed in the leaves of the tolerant wheat cultivar than in those of the sensitive one, whereas the degradation of Fe-protein complexes occurred independently of the cultivar sensitivity.

CONCLUSION

The changes in the quantity of stable, organic radicals formed by stabilizing reactive oxygen species on biochemical macromolecules, indicated greater potential for their generation in leaf tissues subjected to foliar ZEA treatment. This suggested an important role of these radical species in protective mechanisms mainly against direct toxin action. The way the defense mechanisms were activated depended on the method of the toxin application.

Translocation of elements and sugars in wheat genotypes at vegetative and generative stages under continuous selenium exposure

BACKGROUND

Biofortification with selenium (Se) elevates its concentration in feed and fodder plants and helps to prevent health problems in animals and humans. The aim of this study was to describe Se-induced modifications in the accumulation of elements important for the proper functioning of wheat, one of the most popular cereals. The presence of Se correlated with carbohydrate synthesis and electron paramagnetic resonance (EPR). This explained the mechanisms of Se's antioxidant activity.

RESULTS

Selenium accumulation in vegetative and generative leaves, and in the grains of three wheat genotypes (cv. Parabola, cv. Raweta and cv. Manu), differing in their stress tolerance and grown hydroponically in the presence of 10 or 20 μM Na₂ SeO_4, , was proportional to its content in the medium. Stronger Se accumulation was typical of a stress-sensitive genotype. Selenium generally promoted the uptake of macronutrients and micronutrients but their distribution depended on tissue and genotype. Changes in the Se-induced EPR signals of paramagnetic metals and organic radicals corresponded with stress tolerance of the tested genotypes.

CONCLUSIONS

Se application increased the accumulation of nutrients and carbohydrates that are vital for proper plant growth and development. Accelerated uptake of molybdenum (Mo), an element improving dietary properties of grains, may be an additional advantage of Se fertilization. The mechanisms of Se-induced changes in removing Mn and iron (Fe) ions from macromolecules may be one of the factors that differentiate plant tolerance to oxidative stress. © 2019 Society of Chemical Industry.

Application of Targeted Metabolomics to Investigate Optimum Growing Conditions to Enhance Bioactive Content of Strawberry

A simple, sensitive, and rapid assay based on liquid chromatography coupled to tandem mass spectrometry was designed for simultaneous quantitation of secondary metabolites in order to investigate the influence of variety and agronomic conditions on the biosynthesis of bioactive compounds in strawberry. For this purpose, strawberries belonging to three varieties with different sensitivity to environmental conditions ('Camarosa', 'Festival', 'Palomar') were grown in a soilless system under multiple agronomic conditions (electrical conductivity, substrate type, and coverage). Targeted metabolomic analysis of polyphenolic compounds, combined with advanced chemometric methods based on learning machines, revealed significant differences in multiple bioactives, such as chlorogenic acid, ellagic acid rhamnoside, sanguiin H10, quercetin 3-O-glucuronide, catechin, procyanidin B2, pelargonidin 3-O-glucoside, cyanidin 3-O-glucoside, and pelargonidin 3-O-rutinoside, which play a pivotal role in organoleptic properties and beneficial healthy effects of these polyphenol-rich foods.

Electron Paramagnetic Resonance (EPR) Spectroscopy in Studies of the Protective Effects of 24-Epibrasinoide and Selenium against Zearalenone-Stimulation of the Oxidative Stress in Germinating Grains of Wheat

These studies concentrate on the possibility of using selenium ions and/or 24-epibrassinolide at non-toxic levels as protectors of wheat plants against zearalenone, which is a common and widespread mycotoxin. Analysis using the UHPLC-MS technique allowed for identification of grains having the stress-tolerant and stress-sensitive wheat genotype. When germinating in the presence of 30 µM of zearalenone, this mycotoxin can accumulate in both grains and hypocotyls germinating from these grains. Selenium ions (10 µM) and 24-epibrassinolide (0.1 µM) introduced together with zearalenone decreased the uptake of zearalenone from about 295 to 200 ng/g and from about 350 to 300 ng/g in the grains of tolerant and sensitive genotypes, respectively. As a consequence, this also resulted in a reduction in the uptake of zearalenone from about 100 to 80 ng/g and from about 155 to 128 ng/g in the hypocotyls from the germinated grains of tolerant and sensitive wheat, respectively. In the mechanism of protection against the zearalenone-induced oxidative stress, the antioxidative enzymes-mainly superoxide dismutase (SOD) and catalase (CAT)-were engaged, especially in the sensitive genotype. Electron paramagnetic resonance (EPR) studies allowed for a description of the chemical character of the long-lived organic radicals formed in biomolecular structures which are able to stabilize electrons released from reactive oxygen species as well as the changes in the status of transition paramagnetic metal ions. The presence of zearalenone drastically decreased the amount of paramagnetic metal ions-mainly Mn(II) and Fe(III)-bonded in the organic matrix. This effect was particularly found in the sensitive genotype, in which these species were found at a smaller level. The protective effect of selenium ions and 24-epibrassinolide originated from their ability to inhibit the destruction of biomolecules by reactive oxygen species. An increased ability to defend biomolecules against zearalenone action was observed for 24-epibrassinolide.

Copper Oxide Nanoparticle Foliar Uptake, Phytotoxicity, and Consequences for Sustainable Urban Agriculture

Throughout the world, urban agriculture supplies fresh local vegetables to city populations. However, the increasing anthropogenic uses of metal-containing nanoparticles (NPs) such as CuO-NPs in urban areas may contaminate vegetables through foliar uptake. This study focused on the CuO-NP transfer processes in leafy edible vegetables (i.e., lettuce and cabbage) to assess their potential phytotoxicity. Vegetables were exposed via leaves for 5, 10, or 15 days to various concentrations of CuO-NPs (0, 10, or 250 mg per plant). Biomass and gas exchange values were determined in relation to the Cu uptake rate, localization, and Cu speciation within the plant tissues. High foliar Cu uptake occurred after exposure for 15 days for lettuce [3773 mg (kg of dry weight)-1] and cabbage [4448 mg (kg of dry weight)-1], along with (i) decreased plant weight, net photosynthesis level, and water content and (ii) necrotic Cu-rich areas near deformed stomata containing CuO-NPs observed by scanning electron microscopy and energy dispersive X-ray microanalysis. Analysis of the CuO-NP transfer rate (7.8-242 μg day-1), translocation of Cu from leaves to roots and Cu speciation biotransformation in leaf tissues using electron paramagnetic resonance, suggests the involvement of plant Cu regulation processes. Finally, a potential health risk associated with consumption of vegetables contaminated with CuO-NPs was highlighted.

Biochemical response of hybrid black poplar tissue culture (Populus × canadensis) on water stress

In this study, poplar tissue culture (hybrid black poplar, M1 genotype) was subjected to water stress influenced by polyethyleneglycol 6000 (100 and 200 mOsm PEG 6000). The aim of the research was to investigate the biochemical response of poplar tissue culture on water deficit regime. Antioxidant status was analyzed including antioxidant enzymes, superoxide-dismutase (SOD), catalase (CAT), guiacol-peroxidase (GPx), glutathione-peroxidase (GSH-Px), glutathione-reductase, reduced glutathione, total phenol content, Ferric reducing antioxidant power and DPPH radical antioxidant power. Polyphenol oxidase and phenylalanine-ammonium-lyase were determined as enzymatic markers of polyphenol metabolism. Among oxidative stress parameters lipid peroxidation, carbonyl-proteins, hydrogen-peroxide, reactive oxygen species, nitric-oxide and peroxynitrite were determined. Proline, proline-dehydrogenase and glycinebetaine were measured also as parameters of water stress. Cell viability is finally determined as a biological indicator of osmotic stress. It was found that water stress induced reactive oxygen and nitrogen species and lipid peroxidation in leaves of hybrid black poplar and reduced cell viability. Antioxidant enzymes including SOD, GPx, CAT and GSH-Px were induced but total phenol content and antioxidant capacity were reduced by PEG 6000 mediated osmotic stress. The highest biochemical response and adaptive reaction was the increase of proline and GB especially by 200 mOsm PEG. While long term molecular analysis will be necessary to fully address the poplar potentials for water stress adaptation, our results on hybrid black poplar suggest that glycine-betaine, proline and PDH enzyme might be the most important markers of poplar on water stress and that future efforts should be focused on these markers and strategies to enhance their concentration in poplar.

Structural and biochemical response of chloroplasts in tolerant and sensitive barley genotypes to drought stress

The aim of this research was to characterize the changes of structural organization of chloroplasts of sensitive (Maresi) and tolerant (Cam/B1) barley genotypes upon soil drought (10days), which was applied in two stages of plant growth, i.e. seedlings and flag leaves. The electron paramagnetic resonance (EPR) technique was used for the determination of changes in the concentration and nature of long-lived radicals and metal ions (Mn, Fe), measured directly in the structures of fresh leaves, occurring after stress treatment. Stronger variations of EPR parameters were found after drought stress application in the flag-leaf phase and for sensitive genotype. Chloroplasts of Cam/B1 were characterized by a larger surface area and less degradation of their structure during drought stress in comparison to Maresi. The data obtained from Raman spectra showed that better stress tolerance of the genotype was accompanied by greater accumulation of carotenoids in chloroplasts and was correlated with an increase in carotenoid radicals. The increase of the value of the electrokinetic potential (relative to control), which was slightly larger for the chloroplasts of Maresi than of Cam/B1, indicated the chemical reconstruction of the membrane leading to a reduction of their polarity during drought action.

The impact of biochemical composition and nature of paramagnetic species in grains on stress tolerance of oat cultivars

The aim of this work was to investigate the relationships between the chemical composition of oat grains and the tolerance to oxidative stress of oat genotypes. The studies were based on the results of biochemical analyses and both EPR and Raman spectroscopies on whole grains and their parts (embryo, endosperm, seed coat) originating from oat genotypes with different sensitivities to stress. We found that the amounts of fats and especially unsaturated fatty acids, proteins rich in glutamic acid and glycine, as well as phenolics and tocopherols were higher in grains of the tolerant genotype. Moreover, fats and proteins were distributed not only in embryos, but also in endosperms. The grains of tolerant genotypes exhibited high antioxidant activity and contained greater amounts of β-glucan. EPR data pointed to higher concentrations of various kinds of stable organic radicals (semiquinone, tyrosyl and carbon-centered radicals) in whole grains (and their parts) of sensitive genotypes. EPR spectra revealed the character of interactions of paramagnetic transition metal ions Fe(III) and Mn(II) with organic and inorganic structures of grains. The quantitative EPR measurements showed the dependence between the amount of radical species and the content of transition metal ions, mainly Fe(III) bonded to inorganic structures.

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.

Changes in polyphenol and sugar concentrations in wild type and genetically modified Nicotiana langsdorffii Weinmann in response to water and heat stress

In this study wild type Nicotiana langsdorffii plants were genetically transformed by the insertion of the rat gene (gr) encoding the glucocorticoid receptor or the rolC gene and exposed to water and heat stress. Water stress was induced for 15 days by adding 20% PEG 6000 in the growth medium, whereas the heat treatment was performed at 50 °C for 2 h, after that a re-growing capability study was carried out. The plant response to stress was investigated by determining electrolyte leakage, dry weight biomass production and water content. These data were evaluated in relation to antiradical activity and concentrations of total polyphenols, selected phenolic compounds and some soluble sugars, as biochemical indicators of metabolic changes due to gene insertion and/or stress treatments. As regards the water stress, the measured physiological parameters evidenced an increasing stress level in the order rolC < gr < WT plants (e.g. about 100% and 50% electrolyte leakage increase in WT and gr samples, respectively) and complied with the biochemical pattern, which consisted in a general decrease of antiradical activity and phenolics, together with an increase in sugars. As regard heat stress, electrolyte leakage data were only in partial agreement with the re-growing capability study. In fact, according to this latter evaluation, gr was the genotype less affected by the heat shock. In this regard, sugars and especially phenolic compounds are informative of the long-term effects due to heat shock treatment.

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.

Involvement of Selenium in Protective Mechanisms of Plants under Environmental Stress Conditions – Review

In recent years there has been growing interest in selenium (Se) as an important micronutrient not only for animals and humans but also for plants. In particular, its protective effect in plants exposed to stress conditions has been suggested. In spite of many studies, the mechanism of Se action is not fully understood. In this review, possible ways of interaction of Se with stress factors leading to optimal growth and development of plants are presented. As the majority of experiments have focused on the effects of Se application under stress conditions induced by heavy metals, special attention is paid to the results obtained in such studies. Changes of physiological and biochemical properties of plant cells, with particular regard to the influence of Se on the activation of enzymatic and non-enzymatic antioxidants under this stress, are summarized. Experiments in which Se was used in some other environmental stresses (drought, UV, cold and high temperature) are also cited. On the basis of the presented literature it is suggested that a positive effect of Se depends on both its doses and on chosen plant genotypes and is mainly connected with activation of antioxidative defense in plant cells.