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Abstract: Selenium (Se) supplied in inorganic form (as selenate or selenite) was shown to decrease mercury (Hg) toxicity by forming HgSe in soils as well as in animal and human tissues, while for plants there is no evidence of Hg-Se complexation. Although Se in not an essential element for plants it was shown to counteract various abiotic stresses when applied at trace amounts. The aim of this work was therefore to study physiological responses and Hg speciation in plant/ fungi-animal food chain. Lettuce (Lactuca sativa) and porcini mushrooms (Boletus edulis) were taken as model plant/ fungal species and Spanish slug (Arion vulgaris) as a model animal species. The plants, fed to the slugs, were grown in HgCl2 contaminated soil or soil from the vicinity of Hg mine in Idrija with traces of HgS and methyl Hg). Physiological parameters of plants and slugs were monitored during the experiment. At the end the biological material was frozen in LN2 and freeze dried. Hg L3-edge (12284 eV) XANES and EXAFS spectra of the biological samples and standards were measured at liquid helium temperature in fluorescence detection mode at the BM30B beamline of the ESRF synchrotron in Grenoble, using the 30-segment germanium solid state detector [1]. The results showed that addition of Se alleviated Hg toxic effects in the food chain started at HgCl2-contaminated soil, while for the soil from Idrija, containing low amounts of highly toxic methyl-Hg, the beneficial effect was less prominent [2]. No Hg-Se complexes were detected in plants, while in mushrooms and slugs the complexation was confirmed. Addition of Se to the plants, however, changed Hg ligand environment in plant tissues from sulphur to nitrogen ligands. Hg and Se both target the -SH functional groups in the plant tissues, so toxic effects of Hg are rather enhanced than alleviated by addition of Se. Nevertheless, the addition of Se to the plants is beneficial for higher trophic levels and lowers Hg toxicity for the primary consumers, the slugs.
Keywords: mercury, toxicity, ligand environment, XANES, EXAFS, food chain, plant, slug, fungi
Published in RUNG: 05.12.2022; Views: 2273; Downloads: 0
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Abstract: The contribution of 1,8-dihydroxy naphthalene (DHN) melanin to cadmium (Cd) tolerance in two dark septate endophytes (DSE) of the genus Cadophora with different melanin content was investigated in vitro. The DSE isolate Cad#148 with higher melanin content showed higher tolerance to Cd than the less melanised Cad#149. Melanin synthesis was significantly reduced by Cd in both isolates with uninhibited melanin synthesis, in a dosedependent manner. Inhibition of melanin synthesis by tricyclazole reduced the relative growth of Cad#148 exposed to Cd and did not affect Cad#149. Cd accumulation was not altered by tricyclazole in the two isolates, but it increased catalase and reduced glutathione reductase activity in more melanised Cad#148, indicating higher stress levels. In contrast, in Cad#149 the enzyme activity was less affected by tricyclazole, indicating a more pronounced role of melanin-independent Cd tolerance mechanisms. Cd ligand environment in fungal mycelia was analysed by extended EXAFS (X-ray absorption fine structure). It revealed that Cd was mainly bound to O- and S-ligands, including hydroxyl, carboxyl, phosphate and thiol groups. A similar proportion of S- and Oligands (~35% and ~65%) were found in both isolates with uninhibited melanin synthesis. Among O-ligands two types with Cd-O-C- and Cd-O-P- coordination were identified. Tricyclazole altered Cd-O- ligand environment in both fungal isolates by reducing the proportion of Cd-O-C- and increasing the proportion of Cd-O-P coordination. DHN-melanin, among other tolerance mechanisms, significantly contributes to Cd tolerance in more melanised DSE fungi by immobilising Cd to hydroxyl groups and maintaining the integrity of the fungal cell wall.
Keywords: DSE, melanin, Cd tolerance, inhibitor tricyclazole, antioxidant enzymes, EXAFS
Published in RUNG: 13.07.2021; Views: 2958; Downloads: 0
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Abstract: Breeding and engineering of biofortified crops will benefit from a better understanding of bottlenecks controlling micronutrient loading within the seeds. However, few studies have addressed the changes in micronutrient concentrations, localization, and speciation occurring over time. Therefore, we studied spatial patterns of zinc and iron accumulation during grain development in two barley lines with contrasting grain zinc concentrations. Microparticle-induced-X-ray emission and laser ablationinductively coupled plasma mass spectrometry were used to determine tissue-specific accumulation of zinc, iron, phosphorus, and sulfur. Differences in zinc accumulation between the lines were most evident in the endosperm and aleurone. A gradual decrease in zinc concentrations from the aleurone to the underlying endosperm was observed, while iron and phosphorus concentrations decreased sharply. Iron co-localized with phosphorus in the aleurone, whereas zinc co-localized with sulfur in the sub-aleurone. We hypothesize that differences in grain zinc are largely explained by the endosperm storage capacity. Engineering attempts should be targeted accordingly.
Keywords: barley (Hordeum vulgare L.), biofortification, grain development, grain loading, LA-ICP-MS, μ-PIXE
Published in RUNG: 20.10.2020; Views: 3717; Downloads: 0
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Abstract: In wheat (Triticum aestivum L.), the awns—the bristle-like structures extending from lemmas—are photosynthetically active. Compared to awned cultivars, awnletted cultivars produce more grains per unit area and per spike, resulting in significant reduction in grain size, but their mineral element composition remains unstudied. Nine awned and 11 awnletted cultivars were grown simultaneously in the field. With no difference in 1000-grain weight, a larger calcium and manganese—but smaller iron (Fe) concentrations—were found in whole grain of awned than in awnletted cultivars. Micro X-ray absorption near edge structure analysis of different tissues of frozen-hydrated grain cross-sections revealed that differences in total Fe concentration were not accompanied by differences in Fe speciation (64% of Fe existed as ferric and 36% as ferrous species) or Fe ligands (53% were phytate and 47% were non-phytate ligands). In contrast, there was a distinct tissue-specificity with pericarp containing the largest proportion (86%) of ferric species and nucellar projection (49%) the smallest. Phytate ligand was predominant in aleurone, scutellum and embryo (72%, 70%, and 56%, respectively), while nucellar projection and pericarp contained only non-phytate ligands. Assuming Fe bioavailability depends on Fe ligands, we conclude that Fe bioavailability from wheat grain is tissue specific.
Keywords: biofortification, phytate, iron, awn, X-ray fluorescence, X-ray absorption spectrometry, phosphorus, sulphur, nicotianamine
Published in RUNG: 16.01.2020; Views: 3680; Downloads: 0
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Keywords: 2D Imiging, XRF, XANES, synchrotron light
Published in RUNG: 05.09.2019; Views: 4125; Downloads: 0
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