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  • Author or Editor: G. Gullner x
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The monoterpenoid (S)-carvone was shown earlier to induce glutathione S-transferase (GST) activity and to attenuate necrotic lesion formation in Tobacco mosaic virus (TMV) inoculated, hypersensitively reacting tobacco Xanthi-nc plants. To explore structure-activity relationships, three monoterpenes and five monoterpenoids were tested for their ability to induce increased GST activity in tobacco leaf discs. (S)-Carvone proved to be the most potent inducer. (S)-Carvone treatments markedly up-regulated the expression of several tobacco GST genes belonging to the phi, tau and theta classes, particularly in the case of tau class GSTs. Furthermore, TMV inoculation slightly induced the transcript abundance of the GSTT2 gene. The expression of three catalase (CAT) genes was also examined in (S)-carvone-treated tobacco leaf discs. The expression of CAT1 was not influenced by (S)-carvone treatments, whereas that of CAT2 was significantly repressed. (S)-Carvone very weakly induced the transcription of the CAT3 gene. The effect of the opposite enantiomer, (R)-carvone on the expression of GST and CAT genes was similar to that of (S)-carvone. Our results suggest that the antioxidative reactions catalyzed by tau and theta class GSTs contribute to the attenuation of necrotic disease symptoms in TMV-inoculated tobacco plants.

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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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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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Fatty acid hydroperoxide-producing lipoxygenase (LOX) and hydroperoxide-degrading glutathione peroxidase (GPOX) enzyme activities were studied in leaves of virus resistant Xanthi-nc and susceptible Samsun-nn tobacco cultivars after inoculation with Tobacco mosaic virus (TMV). Total LOX activity showed a maximum at pH 5.5 in cell-free extracts of uninfected leaves. LOX activity markedly increased at this pH after TMV inoculation, but a substantial induction was detected also in the basic pH range with an emerging peak around pH = 8.5. TMV-elicited LOX induction was weaker and appeared later in Samsun-nn than in Xanthi-nc leaves. GPOX activity was also substantially induced by TMV infection. However, this induction appeared only 4 days post-inoculation in resistant Xanthi-nc plants in tissues surrounding the localized necrotic lesions. In contrast, GPOX activity did not change in TMV-inoculated, susceptible Samsun-nn leaves. Several glutathione S-transferase (GST) isoenzymes also display GPOX activity. The expression of a tau class GST gene was markedly induced by TMV inoculation in Xanthi-nc leaves. This tobacco GST gene was partially cloned and sequenced.

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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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