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Acta Phytopathologica et Entomologica Hungarica
Authors:
A. P. Glinushkin
,
O. O. Beloshapkina
,
A. A. Solovykh
,
V. S. Lukyantsev
,
A. A. Batmanova
,
G. V. Sudarenkov
, and
J. Molnár

The identification of pathogenic agents isolated from infected wheat seeds and plants, collected in the Southern Ural and characterized by an atypical manifestation of bacterial infection (yellow leaf tips), has been carried out by direct microbiological and molecular methods. In addition, an indirect identification by the hypersensitive reaction (HR) approach has been performed simultaneously with the pathogenicity assessment of isolates using an indicator plant Plectranthus australis R. Br. Isolated samples have been microbiologically identified as Xanthomonas sp. According to the results of the PCR identification with species-specific primers, isolated samples represent Xanthomonas translucens; the reliability of the obtained results is corroborated by the hypersensitive reaction approach used also to assess the pathogenicity of isolates. Winter wheat, especially cv. Pionerskaya 23, where both X. translucens and Pantoea agglomerans were found, suffered more severe symptoms than spring wheat that was only affected by strains of X. translucens. To improve the reliability of the primary diagnostics of a bacterial character of seed infection, the provoking of the pathogen development by temperature or pH stress is proposed.

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Acta Agronomica Hungarica
Authors:
J. Szarka
,
O. Toldi
,
E. Szarka
,
J. Remenyik
, and
et al.

The fact that production is often unsuccessful even when resistant varieties are selected on the basis of the hypersensitive reaction can be attributed to the lack of adequate knowledge on plant disease resistance. In addition to specific plant responses to pathogen species, plants also possess an aspecific defense reaction which, instead of causing rapid tissue destruction, is based on the opposite strategy, protecting the plant against attack by microbes through tissue compaction achieved by cell enlargement and cell division. Genetic analyses carried out in pepper revealed that the general defense reaction was inherited as a monogenic recessive trait (gds). Pathophysiological observations indicate that the stimulus threshold is lower and the reaction rate faster than for specific defense reactions. Biochemical analyses suggest that, unlike plants exhibiting rapid tissue destruction, plants containing the gds gene do not require an oxidative burst elicited by hydrogen peroxide to stimulate the defense mechanism. It was also found that the regulation of the general defense system involves metabolic pathways that are independent of salicylic acid. The general and specific plant reactions form an integrated system of plant defense.

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It is established that the central area of TMV-induced local lesions developed in detached Datura stramonium leaves, along with the completely collapsed cells (types I and II), contains cells (type III) conserving to a certain degree integrity of their structural components. A characteristic of the type III cells was the accumulation of considerable amount of virus and formation of TMV-specific granular and tubular inclusions. The study of lesion development showed that a proportion of the collapsed cells and cells of type III did not essentially change in the period up from 3 to 5 days after infection of the leaves. These data suggest that the disease development in cells of type III does not lead to a hypersensitive response and is very similar to that in the systemically infected cells.

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The tomato spotted wilt disease caused by tospoviruses in tomato is an important viral disease. Artificial screening of tomato wild species and cultivars for resistance to tospoviruses revealed the wild species Lycopersicon peruvianum to be resistant to tospovirus infection. The protein profile in L. peruvianum showed additional proteins of molecular sizes of 45kDa, 34kDa and 26kDa and an additional 55kDa protein was detected in L. pimpinellifolium . The peroxidase isozyme pattern was also found to be distinct in L. peruvianum . cDNAs of R genes coding for tospovirus resistance were isolated from the wild species, L. peruvianum (TNAU T). The partial cDNAs were cloned in the vector pTZ57R/T, sequenced and characterized. The tomato varieties, hybrid and wild species L. pimpinellifolium selected in this study were susceptible to tospovirus infection and did not show presence of R genes. Sequence analysis of the partial cDNAs corresponding to the R genes isolated from the wild species L. peruvianum showed considerable homology on the protein level with already available resistance proteins like late blight resistance protein, root knot nematode resistance protein, potato disease resistance protein, Hero protein confirming resistance against potato cyst nematode, and Prf protein confirming resistance against Pseudomonas syringae pv. tomato . In the present study, R genes effective against tospoviruses were isolated and characterized from a wild species of tomato. These results have important impact in terms of transformation strategies to develop tospovirus resistant transgenic plants.

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f. sp. tritici HR hypersensitive reaction PAGE polyacrylamide gel electrophoresis Pgt Puccinia graminis f. sp. tritici Pt Puccinia triticina RNase ribonuclease RT-qPCR real-time, quantitative PCR References Ádám , A.L. , Galal , A

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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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The recent review summarizes the major achievements in discovery of role of phytoglobins in mediation of nitric oxide generated cellular functions in higher plants. Genes encoding non-symbiotic hemoglobins have been cloned from several plant species. The expression pattern of these genes show tissue-specificity that is also under the control of stress factors like hypoxia. The nitric oxide has pivotal role in signalling pathway specifically in hypersensitive reactions and programmed cell death. Production of transgenic tobacco plants overexpressing the alfalfa hemoglobin showed altered necrotic symptoms after treatment with nitric oxide generating compounds or infection by necrotic pathogens. The present review helps to outline the similar relation between hemoglobin and nitric oxide in plants as it was found in animal cells.

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changes in peroxidase activity accompany hydrogen peroxide generation during the development of a nonhost hypersensitive reaction in lettuce . Plant Physiol . 118 : 1067 – 1078

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. Pellegrini , L. , Rohfritsch , O. , Fritig , B. , Legrand , M. ( 1994 ) Phenylalanine ammonia-lyase in tobacco . Molecular cloning and gene expression during the hypersensitive reaction to tobacco mosaic virus and the response to a fungal elicitor

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) Localization, conjugation and function of salicylic acid in tobacco during the hypersensitive reaction to tobacco mosaic virus. Proc. Natl. Acad. Sci. USA 89 , 2480–2484. Fuhrer, J., Skarby, L., Ashmore, M. R. (1997

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