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  • Author or Editor: T. Kômíves x
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In recent years, the importance of the endogenous plant tripeptide glutathione (GSH) has been increasingly recognized in plant-pathogen interactions due to its contribution to various signaling and defense mechanisms. In this paper the recent developments in the research for possible roles of GSH in infected plants are summarized. GSH participates not only in antioxidative and detoxification reactions but also in redox regulation of the expression of protective genes in infected cells. Several lines of evidence suggest that glutathione S-transferase (GST) isoenzymes also have an important role in plant disease resistance, but their exact functions have remained elusive.

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The uptake of persistent organic pollutants (POPs) from soil by plants allows the development of phytoremediation protocols to rehabilitate contaminated areas. In this study theoretical descriptors have been employed as independent variables for developing quantitative structure-activity relationship (QSAR) models for predicting the bioconcentration factors (BCFs) of POPs in different plants. A quantitative estimation has been given on the molecular properties of POPs in terms of theoretical molecular descriptors that are relevant to the uptake from soil and pharmacokinetic behavior in plants. The study resulted in statistically significant linear regression models developed for the BCF values of 20 polychlorinated dibenzo-p-dioxins/dibenzofurans and 14 polyhalogenated biphenyls in two zucchini varieties based on retrospective data. The parameters have been selected from a set of 1660 DRAGON, 150 VolSurf and 11 Quantum Chemical descriptors. The best regression model (Eq. 1), employing VolSurf, DRAGON GETAWAY and quantum chemical descriptors, displayed the following highly significant statistical parameters: n=27, R 2=0.940, SE=0.155, F=392.1, q 2=0.922; external validation set: n=7, R2=0.739, q2=0.47, SE=0.338, F=14.2 It is suggested that the QSAR models proposed might contribute to the development of workable soil remediation strategies.

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A pot experiment was designed to study the variability of some inside and outside mycorrhizosphere characteristics of barley (Hordeum vulgare L.) and the potential transfer of Cd, Ni and Pb in a metal-contaminated calcareous chernozem soil. Substrates of the pots were taken from a long-term field experiment site at Nagyhörcsök, Hungary, where the cadmium (Cd), nickel (Ni) and lead (Pb) were spiked as single salt application at four levels (0, 30, 90 and 270 mg kg−1 dry soil) 12 years prior to this study. Beside the biomass production and element content of plants, the total catabolic enzyme activity measured by fluorescein diacetate analysis (FDA) and the colonization parameters of arbuscular mycorrhizal fungi (AMF); the infection intensity (M%) and the arbusculum richness (A%) were determined. After 12 years, the indigenous mycorrhiza fungi in the soils might be adapted to the contaminated environments, as a function of metals and their applied doses. Stress-defense strategies of the fungal-plant symbiosis, such as the better functioning of the AMF by enhanced arbusculum richness or by the improved phosphore-mobilization capacity was found mainly at the middle (90 mg kg−1) doses of metals. Increasing quantity of Cd above the maximum permitted concentration in the soil could enhance the biomass production of barley roots and reduce the Cd translocation towards the shoots. Outside rhizosphere parameters as the FDA enzymatic activity were stronger influenced by the long-term metal stress, than the inside mycorrhiza colonization, showing the protecting effect of the symbiosis both for the macro- and microsymbionts. Mycorrhizosphere conditions are part of the common plant-microbe strategies and plant-defending mechanisms that can result in a better stress-alleviation at chronic metal-exposures.

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Total mineral uptake capacity of zucchini (Cucurbita pepo L. cv. giromontiina) grown in an experimental field at Gödöllő was studied. The mineral content of the soil (brown acidic sandy forest soil) showed unexpectedly high content (mg kg−1 DW) of Ba (95.5), Cr (32.9), Ni (27.8), Pb (15.4) and Zn (53.3). Boron (B) concentration of the soil was relatively low (7.1 mg kg−1 DW), but its bioaccumulation content in root, (2.5) shoot, (33.1) and leaf (50.1) tissues of the plant (mg kg−1 DW). Zinc (Zn) was also bioaccumulated in the plant with contents (mg kg−1 DW) of 47.1 (roots), 23.0 (shoots) and 56.1 (leaves) as compared with 53.3 (in the soil). Toxic element exclusion was observed in zucchini (mg kg−1 DW) concerning Ba (29.0), Co (0.2), Cr (5.3), Ni (5.8) and Pb (3.4) measured in the roots when compared with their concentrations in the soil: Ba (95.5), Co (10.2), Cr (32.9), Ni (27.8) and Pb (15.4). In silico sequence analyses of nucleotide and amino acid sequences of aquaporins (NIP, TIP, SIP and Si-TRP), boron-exporters (BOR), and rbcL of cpDNA revealed plant species with high sequence similarities to the sequences of Cucurbits, which predicted additional plants with intensive mineral (B and Zn) uptake capacity, similar to Cucurbits with phytoextraction potential.

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As DNA methylation patterns are inherited (‘epigenetic memory’) gsh I transgenic poplar ( Populus × canescens ) clones (11 ggs and 6 Lgl ) were treated with the DNA demethylating drug DHAC (5,6-dihydro-5′-azacytidine hydrochloride) at 10 −4 M for 7 days in order to study acquired plant molecular defense mechanisms in novel plant sources. In this study, the response of relative gene expression levels of transgene gsh I and poplar gene gsh 1 to DHAC treatment were analyzed by qRT-PCR ( q uantitative r everse t ranscriptase PCR). High expression levels of transgene gsh I were observed in the 6 Lgl clone (13.5-fold increase) compared to 11 ggs (1.0) sample. The expression level doubled (1.8-fold increase) in the DHAC-treated 6 Lgl samples but not in the 11 ggs clone (0.4-fold). Contrary to this, the relative copy number of transgene gsh I in the 6 Lgl clone was found to be 60% less (1.0) than in the 11 ggs sample (1.6). Relative expression level of endogenous poplar gene gsh 1 showed significantly higher responsiveness to DHAC-induced demethylation than the transgene gsh I with the highest expression level in the untransformed WT poplar (19.7-fold increase) compared to transformed clones of 6 Lgl (8.7-fold increase) and 11 ggs (2.5-fold increase), respectively. Competition in the reactivation capacity between transgene gsh I and poplar gsh 1 of 6 Lgl clone was also observed as the relative gene expression level of transgene gsh I increased from a high relative expression level (13.5) up by about twofold (1.8 times) rate (to 23.7) compared to poplar gsh 1 gene that increased by an 8.7 increment from a lower level (1.6 rel. expression) to 13.9.

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