| الوصف: |
Namen doktorske disertacije je bil proučiti, kako dodatek selena (Se) vpliva na privzem, vezavne oblike in biodostopnost živega srebra (Hg) v rastlinah, glivah in modelnih živalih, polžih lazarjih. Rastline smo gojili na naravno (Idrija) ali umetno (HgCl2) onesnaženi zemlji, glive v tekočih ali trdnih gojiščih, onesnaženih s HgCl2 ali HgS, brez ali ob dodatku Se. Nekatere glive smo nabrali na s Hg neonesnaženih in s Hg onesnaženih (Idrija) območjih. Ob koncu poskusov smo opazovali morfološke in biokemijske spremembe v organizmih, kot so spremembe sveže in suhe biomase posameznih organov (poganjkov in korenin rastlin ter hepatopankreasov in mišic polžev) oz. micelijev gliv, koncentracije klorofilov v poganjkih ter stopnjo stresa v tkivih preko koncentracije malondialdehida. V liofiliziranem materialu smo izmerili koncentracije Hg in Se. Vezavne oblike Hg v organih smo določali s pomočjo absorpcijske spektroskopije. Ugotovili smo, da je bila biodostopnost Hg za rastline in glive odvisna od vezavne oblike Hg v substratu oz. gojišču (HgCl2 ali HgS - Idrija). Biofortifikacija rastlin s Se ni vplivala na biodostopnost Hg za rastline, je pa uživanje s Se obogatene rastlinske hrane povečalo biodostopnost Hg za polže. Za prehranjevanje uporabljene rastline, gojene na HgCl2 z dodanim Se, so pri polžih omilile poškodbe povzročene s Hg, medtem ko je uživanje rastlin, gojenih na HgS z dodanim Se, poškodbe povečalo. Gobe iz Idrije so nakopičile visoke koncentracije Hg, prav tako gobe iz neonesnaženih območij (NP). V gobah iz NP se je Hg večinoma vezal na di-tiolne ligande in HgSe, medtem ko so v idrijskih gobah deleži HgSe in tetra-tiolnih ligandov narastli z naraščanjem koncentracij Hg v tleh. Živo srebro v gobah je bilo za polže biodostopno. Biodostopnost Hg se je zmanjšala s povečevanjem Se v gobah preko povečane tvorbe kompleksa HgSe v gobah. Zaščitni učinki Se pred Hg so se ob uživanju idrijskih gob kazali v povečanju stopnje rasti polžev in zmanjšanju tvorbe malondialdehida kot indikatorja stopnje stresa v tkivih. Postopki kuhanja gob v vodi ali 9 % ocetni kislini so biodostopnost Hg za polže povečali, a hkrati zmanjšali končne koncentracije Hg v njihovih organih. The effects of selenium (Se) addition to leaves (plants) or substrate (plants or fungi) on mercury (Hg) uptake, transfer, ligand environment and toxicity in the plant/fungi-slug food chain were studied. Plants were grown on naturally (HgS, Idrija) or artificially (HgCl2) contaminated substrate, without or with foliarly applied Se. Fungi were grown in liquid media or on agarose plates, with addition of HgCl2 or HgS and with or without added Se. Additionally, fungi (Boletus spp. and Scutiger pes-caprae) were picked from the forest from non-polluted (NP) or Hg-polluted (Idrija) sites. At the end of experiments morphological and biochemical changes were observed as fresh and dry biomass (plant shoots and roots fungal mycelium slug hepatopancreas and muscle), concentrations of photosintetic pigments in shoots and concentrations of malondialdehyde (MDA) as a measure of oxidative stress in the observed tissues. Mercury and Se concentrations were measured in freeze-dried and pulverised material. Ligand environment of Hg was studied using synchrotron based X-ray absorption spectroscopy. We showed that Hg bioavailability (BA) for plants and fungi depended on Hg speciation in substrate or growth medium. Selenium biofortification had no effect on Hg BA for plants, while the Se addition increased the BA of Hg for slugs with an opposite physiological response. Feeding on biofortified plants from Idrija soils increased toxicity in slugs, but alleviated it when ingesting HgCl2 exposed biofortified plants. Boletus spp. accumulated significant amounts of Hg, especially the ones from Idrija. Also, S. pes-caprae accumulated significant amounts of Hg at NP. Mercury in examined fungi from NP was mainly bound to di-thiolate and HgSe ligands, while at Idrija site the proportion of HgSe and tetra-thiol ligands increased with increasing Hg contents in the fungi. Experiments with the slugs showed that Hg present in fungi was in bioavailable form as it accumulated in their hepatopancreas and muscle tissues. The BA of Hg increased when fungi, cooked in water or acetic acid, were ingested, but final Hg concentrations in hepatopancreas decreased. The toxic effects of Hg exhibited as reduced growth and increased MDA level in the slug’s hepatopancreas counteracted with increasing Se concentrations in the ingested fungi, pointing to a protective role of Se against Hg toxicity through HgSe complexation. |
