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The aim of this work was to examine the multiplication of the common duckweed (Lemna minor), an aquatic plant species widespread in European stagnant waters, in two different media (Murashige – Skoog and Hoagland) with and without phenol supplementation. In order to quantify plant multiplication we have used relative growth rate and tolerance indices on both tested media and at five phenol concentrations (10, 15, 20, 30 and 100 mg/L). Furthermore, we examined the possibility of phenol removal from aqueous media containing different phenol concentrations, by using plant/bacteria system consisting of the duckweed and its naturally occurring microbial populations. After 7 days, number of newly formed fronds was approximately four times higher than at the beginning of the experiment on both tested media. The most important result in this study was removal of 70% of phenol from the highest initial concentration of 100 mg/L, in mixed cultures of duckweed and bacteria. By comparison, aseptic duckweed cultures removed approximately 50% of phenol at the same initial concentration. Our duckweed specimen showed a fast reproduction rate, high tolerance to phenol and a possible cooperation with rhizosphere-associated bacteria. All of these traits can be ultimately utilized for bioremediation purposes.
In this work, we demonstrate that the rhizosphere of common duckweed (Lemna minor) is inhabited with various phenol-resistant bacterial strains. Based on 16S rRNA sequencing, we have identified 60 rhizosphere-associated bacterial isolates belonging to 10 different bacterial genera (Pseudomonas, Hafnia, Serratia, Enterobacter, Micrococcus, Stenotrophomonas, Xanthomonas, Bacillus, Staphylococcus and Klebsiella). All isolates have been tested for phenol resistance and ability to utilize phenol as the sole carbon source. 70% of all isolates survived high doses of phenol (≥200 mg/L) and at least 27% can be potentially acclimatized by gradual increase of phenol concentration. Finally, based on high phenol resistance, ability to utilize phenol as the sole carbon source and documented low pathogenicity, we propose 5 strains as potentially excellent candidates for bioremediation. These 5 strains taxonomically correspond to Klebsiella sp., Serratia sp., and Hafnia sp., respectively. To the best of our knowledge, this is the first attempt to assess decontamination capacity of Serratia nematodiphila and Hafnia sp. in the context of bioremediation of phenol-contaminated aqueous media. Although additional analyses are needed, interaction between the common duckweed and the selected bacterial strains may be utilized in future bioremediation strategies.
Juglone (JU; 5-hydroxy-1,4-naphthoquinone) is an allelochemical synthetized by a wide range of Juglandaceae members. This compound evokes a wide array of detrimental effects in susceptible acceptor plants, including growth inhibition and impairments in the course of biochemical and physiological processes. Therefore, juglone may be considered as a potential bioherbicide in weed control in cereal crops. The purpose of our study was to determine the influence of JU treatment on the content of superoxide anion radical (O2•−) - sensitive and early marker of oxidative stress, and the activity of superoxide dismutase (SOD) - enzyme that functions as a crucial component of the first line antioxidative defense in seed tissues. In the study we tested seeds of four selected plant species of cereal agrosystem: corn poppy (Papaver rhoeas L.), corn cockle (Agrostemma githago L.), spring wheat (Triticum aestivum L., cv. Nawra), and spring oat (Avena sativa L., cv. Maczo). Additionally, the allelopathic influence of JU on seed germination of the studied plant species was investigated. The seeds were exposed to three examined juglone concentrations: 0.001, 0.1, and 10 mM (4% methanoldeionized water solutions), whereas the control seeds were treated with aqueous methanolic solutions (4%). Obtained results evidenced much more severe suppression of germination process and robust generation of superoxide anion radical in the tested weeds, compared to the cereals, and the crucial role of superoxide dismutase in limiting the juglone-induced oxidative stress in the studied seeds.
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