mlo5, a resistance gene effective against a biotrophic pathogen (Blumeria graminis fsp. hordei) confers enhanced susceptibility of barley to the necrotrophic fungus Bipoláris sorokiniana (teleomorph: Cochliobolus sativus)

The barley resistance gene m/o5 determines race non-specific resistance to the biotrophic powdery mildew pathogen Blumeria graminis f.sp. hordei. On the other hand, we have shown that barley lines that contain the mlo5 gene display enhanced susceptibility to the necrotrophic fungus Bipoláris sorokiniana (teleomorph: Cochliobolus sativus) and its toxic culture filtrate (Kumar et al. 2001). Enhanced susceptibility to necrotic disease symptoms was linked to increased accumulation of hydrogen peroxide (H}02), a reactive oxygen intermediate. In addition, increased accumulation of transcripts of a barley pathogenesis-related gene (PR1-b) and slight increases in expression of two antioxidant genes, a glutathione S transferase and an ascorbate peroxidase occurred in association with enhanced cell/tissue death and Hj02 accumulation. These results might reflect an unsuccessful attempt by infected m/o5-barley to suppress necrotic disease symptoms and support the hypothesis that the barley Mlo gene product functions as a negative regulator of cell death. Therefore, a compromised Mlo pathway confers effective control of the biotrophic powdery mildew pathogen but not of the necrotroph B. sorokiniana, demonstrating the necessity of different host defense strategies in response to pathogens with different lifestyles (biotroph vs. necrotroph)

Induction of hypersensitive necrosis at high temperatures by generation of reactive oxygen forms in virus resistant tobacco

Tobacco (Nicotiana tabacum cv. Xanthi nc) resistant to Tobacco mosaic virus (TMV) displays a hypersensitive response (HR) following virus infection, characterized by localized necrotic lesions around infection sites at ambient temperatures (e.g. 20°C). We have demonstrated that application of chemical compounds that generate reactive oxygen species (ROS), such as the riboflavin/methionine and glucose/glucose oxidase systems or H2O2 treatment induce HR-type necroses in leaves of Xanthi-nc tobacco infected with TMV even at high temperatures (30°C), when both necrosis and virus resistance are impaired. It was possible to suppress chemically induced HR-type necrotization at 30°C by application of antioxidants like superoxide dismutase (SOD) and catalase (CAT). Importantly, high TMV levels at 30°C did not differ in infected plants, regardless of the presence or absence of HR-type necrotization. Levels of one of the ROS, superoxide (O2·-), activity of NADPH-oxidase and expression of a tobacco NADPH-oxidase gene responsible for O2·-production were significantly lower in leaves of infected and healthy Xanthi-nc tobacco at 30°C, as compared to 20°C. It is concluded that development of HR-type necroses caused by TMV infection depends on a certain level of superoxide and other ROS, while suppression of virus multiplication in resistant tobacco is associated with low temperature but seems to be independent of HR-type necrotization

The Silencing of (Trans)Gens – A mechanism of Virus Resistance in Plants

Gene silencing and RNA-mediated virus resistance are two remarkable and potentially useful phenomena that occur in higher plants.However,in light of recent research it seems likely that the post- transcriptional type of gene silencing and RNA-mediated virus resistance are actually manifestations of the same phenomenon.The occurrence of both post-transcriptional gene silencing (PTGS)and RNA-mediated virus resistance require sequence homology between a transgene and an endogenous gene or a transgene and an infecting virus,respectively.Furthermore,both processes are characterized by high transcription rates of homologous,silenced (trans)genes but low steady-state levels of their transcripts (in case of virus- infected plants,low steady-state transcript levels of the silenced transgene and homologous viral RNA which eventually leads to virus resistance).Therefore,PTGS is a potential tool for creating virus-resistant transgenic plants that express a sequence homologous to the invading virus.It is very unlikely,though,that PTGS in plants has evolved solely for the purpose of transgene suppression so it is perhaps not surprising that some natural virus defense systems have been found to resemble gene silencing.In addition,although plants may combat virus infections by gene silencing,there is recent evidence that some plant viruses can fight back by suppressing the plant 's ability to carry out the silencing process.The advantages and disadvantages of the commercial use of PTGS for creating virus-resistant plants (RNA-mediated virus resistance)is also discussed

A szisztemikus szerzett rezisztenciában szerepet játszó molekuláris mechanizmusok vizsgálata = A study of molecular mechanisms involved in systemic acquired resistance

A növények ellenálló képessége kórokozókkal és abiotikus stressz tényezőkel szemben is fokozható megfelelő kémiai kezeléssel vagy fertőzéssel. A szisztemikus szerzett rezisztencia (SAR) mechanizmusainak mélyebb megismerése végett egyszikű és kétszikű növényeket és különböző SAR-indukáló kezeléseket vontunk be kísérleteinkbe. Fokozott antioxidáns kapacitást mutattunk ki dohánynövényekben kórokozóval és kémiai szerekkel aktivált rezisztencia esetében egyaránt. Az alternatív oxidáz és a glutation S-transzferáz indukcióját a génexpresszió szintjén is ki tudtuk mutatni. Ezzel szemben az árpa csak a Piriformospora indica gombával történt fertőzés hatására tett szert nagyobb antioxidáns szintre, míg a 2,6-diklór-izonikotinsav hatására kialakuló rezisztencia nem járt együtt ilyen jellegű változással. Fontosnak tartom kiemelni, hogy a P. indica gombával kezelt árpa jobban tűrte a só (NaCl) jelenlétét a talajban, ami előnyt jelenthet egy kedvezőtlen talajon folyó növénytermesztés során. A P. indica gomba által indukált rezisztenciát tovább szeretnénk vizsgálni egy új OTKA pályázat keretében. | Treatments of plants with appropriate micro-organisms or chemicals can induce elevated level of resistance against both pathogens and abiotic stress factors. Monocot and dicot plant species and different inducers of systemic resistance (SAR) have been tested to get deeper insight into the mechanisms of SAR. We have detected elevated levels of antioxidant defence capacity in tobacco plants possessing SAR upon induction by a pathogen or chemicals. We have found that genes of alternative oxidase and glutathione S-transferase were expressed at high levels. However, systemic induction of resistance in barley was associated with higher antioxidative defence induced by a micro-organism, Piriformospora indica, but not that induced by a chemical 2,6-dichloroisonicotinic acid. Importantly, barley plants infested by P. indica became more tolerant to salt (NaCl) stress, which provides a great advantage in unfavourable soil conditions. Mechanisms of P. indica-induced resistance should be further investigated in future studies supported by OTKA

A növényi gén-indukció szerepe a nekrózis-gátlással együttjáró rezisztenciaformákban = The role of plant gene induction in resistance forms that result in necrosis inhibition

Az általunk korábban előállított Nicotiana edwardsonii var. Columbia interspecifikus hibrid növényekben egy genetikailag meghatározott, állandóan aktivált állapotú ''szerzett'' rezisztencia működik. Kimutattuk, hogy ez a rezisztencia egyaránt hatásos vírus-, gomba- és baktérium kórokozók, valamint abiotikus stresszek (herbicidek) által indukált nekrotikus tünetek ellen. Dohány nekrózis vírus (TNV) fertőzésnél a rezisztencia nemcsak a nekrotikus tüneteket, de a fertőző kórokozó replikációját is gátolja. Igazoltuk továbbá, hogy ebben a nekrózis-gátlással együtt járó rezisztencia formában kulcsszerepet játszik a magas szalicilsav-szint és egyes antioxidánsok. Az egyik legmegbízhatóbb rezisztencia-marker (PR-1 fehérje túltermelése) egygénes, dominánsan öröklődő tulajdonság. A gyakorlat számára fontos lehet a 'Columbia' növényekhez hasonló tulajdonságokat mutató termesztett növényvonalak előállítása, amelyek fokozottan ellenállnak különféle nekrózissal együtt járó betegségeknek és stresszeknek, de emellett agronómiai tulajdonságaik (pl. zöldtömeg és/vagy termésmennyiség, stb.) nem romlanak le. | We have previously created the interspecific hybrid Nicotiana edwardsonii var. Columbia that displays a genetically determined, constantly activated ''acquired'' resistance. In the framework of this grant we have shown that this type of resistance is effective against necrotic symptoms caused by viral-, bacterial- and fungal pathogens and abiotic (herbicide) stresses. During infection by Tobacco necrosis virus (TNV) the resistance of 'Columbia' plants inhibits both necrotization and viral replication. Furthermore, it was demonstrated that high salicylic acid levels and certain antioxidants play a key role in this type of resistance. One of the most reliable resistance markers (overproduction of the PR-1 protein) is a monogenic, dominant trait. The generation of crop lines with multiresistance similar to that of 'Columbia' plants could be of pivotal importance when the goal is to achieve resistance to several diseases and stresses while maintaining agronomic traits (e.g. green mass and/or fruit and seed quantity etc.)

A lipoxigenáz izoenzimek és az oxilipinek szerepének vizsgálata bab és dohánynövények betegségellenállóságában = The role of lipoxygenase isoenzymes and oxylipins in disease resistance of bean and tobacco

A lipoxigenáz (LOX) enzimek és az általuk termelt lipid-hidroperoxidokból enzimatikus úton képződő, változatos szerkezetű oxilipinek jelentős szerepet játszanak a vírusfertőzött dohány és paprikanövények védekezési reakcióiban. A vírusfertőzött dohány és paprika levelekben mind a 9- mind a 13-LOX enzimek aktivitása megemelkedik. Az inkompatibilis gazdanövény-kórokozó kapcsolatokban (a rezisztens növényekben) az aktivitás emelkedése gyorsabban és nagyobb mértékben jelentkezik, mint kompatibilis kapcsolatokban. A vírusfertőzött rezisztens paprika levelekben több LOX kódoló gén expressziója erősen megemelkedik. Tömegspektrometriás mérésekkel kimutatható volt, hogy egyes illékony vegyületek, így a 2,4-hexadienal, az alfa-jonon és a pentadekanal mennyisége jelentősen megemelkedett a vírusfertőzés következtében. Ezek az eredmények azt mutatják, hogy az oxilipinek mellett terpenoid jellegű vegyületek is felhalmozódnak a vírusfertőzött levelekben. Kimutattuk a divinil-éter szintetáz (DES) gén és egy patatin-szerű lipáz gén szerepét a vírusfertőzött paprikalevelek védekezési reakcióiban. Meghatároztuk a DES gén kódoló régiójának teljes szekvenciáját. Bablevelekben szintén megemelkedett a lipoxigenáz aktivitás a biotróf rozsdagomba Uromyces phaseoli által okozott fertőzés hatására. | Lipoxygenase (LOX) enzymes and oxylipins play important roles in the defense reactions of virus-infected pepper and tobacco plants. Oxylipins are produced from LOX-derived lipid hydroperoxides. In virus infected pepper and tobacco leaves the activities of both 9- and 13-LOX enzymes were significantly elevated. In incompatible plant-virus interactions the increase of LOX activity is much stronger and appears more rapidly than in compatible interactions. In virus infected resistant pepper leaves the expression of several individual LOX coding genes was markedly up-regulated. Mass spectrometric studies showed the accumulation of the volatile 2,4-hexadienal, alpha-ionone and pentadecanal in virus infected resistant pepper leaves. These results showed that beside oxylipins also terpenoid compounds accumulated in pepper leaves following virus infections. We demonstrated the significant role of a divinyl ether synthase (DES) and a patatin-like lipase in virus infected pepper leaves. The entire coding region of DES gene was sequenced. Markedly elevated LOX activities were found also in bean leaves inoculated with the biotrophic rust fungus Uromyces phaseoli

Prooxidáns és antioxidáns növényi gének a nem-gazda betegségrezisztenciában - funkció meghatározás géncsendesítéssel = Prooxidant and antioxidant plant genes in non-host resistance - functional identification by gene silencing

Prooxidáns, antioxidáns és programozott sejthalállal kapcsolatos gének mRNS-szintű kifejeződését vizsgáltuk az ún. nem-gazda rezisztenciában (=rezisztencia a más növényfajokat fertőző kórokozókkal szemben), vírus-, baktérium- és gomba kórokozókkal fertőzött dohányfélékben (Nicotiana spp.) és árpában. Kimutattuk, hogy a prooxidáns/antioxidáns egyensúly ebben a hatékony, gyors lefolyású rezisztenciaformában is döntő szerepet játszik: a prooxidánsok - elsősorban a szuperoxid - korai felhalmozódását antioxidáns (pl. szuperoxid-dizmutáz, glutation-S-transzferáz) és sejthalál-gátló (BAX inhibitor) gének által termelt fehérjék ellensúlyozzák. Kutatásaink szerint tehát a nem-gazda rezisztencia egyik kulcslépése lehet a kórokozókat gátló korai prooxidáns-felhalmozódás, ill. ezzel egyidőben a megtámadott növény antioxidáns kapacitásának gyors indukciója. Igazoltuk, hogy egy vírus kórokozó (TMV) ellen ható rezisztencia gén (N) terméke egy nem-gazda rezisztenciát előidéző másik vírus (TNV) fertőzésekor pontosan ellenkező hatást válthat ki, ugyanis fogékonysági faktorként hathat. Az N gént Nicotiana edwardsonii növényekben csendesítve (expresszióját gátolva) ugyanis a TMV-vel szembeni rezisztencia sérült, a TNV-vel szembeni nem-gazda rezisztencia viszont fokozódott. A vírusokkal szembeni nem-gazda rezisztenciát befolyásoló növényi gének azonosítása/jellemzése a jövő rezisztencia-nemesítését teheti még eredményesebbé. | We have investigated expression of plant genes involved in prooxidant and antioxidant effects and inhibition of programmed cell death during non-host resistance (i.e. resistance to pathogens that infect other plant species) to viral, bacterial and fungal pathogens in Nicotiana spp. and barley. We have shown the pivotal role of prooxidant/antioxidant balance during this quick and effective form of resistance: the early accumulation of prooxidants - primarily superoxide - is counteracted by proteins encoded by antioxidant (e.g. superoxide dismutase and glutathione S-transferase) and cell death inhibitor (BAX inhibitor) genes. According to our research a key component of non-host resistance could be the early prooxidant accumulation that inhibits pathogens and the quick induction of the antioxidant capacity of attacked plants. We have pointed to the fact that the product of a plant resistance gene (N) effective against a virus (TMV) could have a completely opposite effect during infection by a virus (TNV) that elicits non-host resistance: in the latter case the same product may function as a susceptibility factor. Following silencing of the N gene in Nicotiana edwardsonii resistance to TMV was compromised, while non-host resistance to TNV was enhanced. Identification and characterization of plant genes that influence non-host resistance to viruses could provide valuable information for resistance breeding in the future

Preformed defense responses in a powdery mildew-resistant Hungarian cherry pepper cultivar

A Hungarian cherry pepper (Capsicum annuum var. cerasiformé) cultivar ('Szentesi') displays resistance to pepper powdery mildew caused by Leveillula taurica. Resistance also develops in susceptible sweet pepper (C. annuum) when grafted on resistant cherry pepper cv. Szentesi rootstocks. Powdery mildew (PM) resistance is correlated with high levels of the defense regulator reactive oxygen species superoxide (O2 ') even in healthy plants. In order to further elucidate the mechanisms of preformed defense responses in cherry pepper cv. Szentesi we have monitored levels of salicylic acid (SA), a key molecule of plant defense signaling and expression of so-called pathogenesis/defense related (PR) genes in healthy pepper plants. Assays of free and bound (glycosylated) SA by high performance liquid chromatography (HPLC) revealed that in leaves of PM-resistant pepper levels of free SA are ca. twice as high compared to that of PM-sensitive plants. No difference occurred in levels of bound (glycosylated) SA. Expression of the CaPR-1 gene was several times higher in leaves of PM-resistant pepper than in sensitive plants as assayed by real time reverse transcription quantitative polymerase chain reaction (real time RT-qPCR). On the other hand, high expression levels of the CaPR-2 (glucanase) gene did not entirely correlate with PM-resistance, being detectable only in PM-resistant cv. Szentesi plants but neither in PM-resistant sweet pepper cv. Totál grafted on cv. Szentesi rootstocks nor in susceptible controls (cv. Totál). It seems that graft-transmissible PMresistance of the cherry pepper cv. Szentesi is correlated not only with high levels of superoxide but also with elevated levels of free salicylic acid and enhanced expression of the defense-related CaPR-1 gene

INVESTIGATION OF THE ENVIRONMENTAL CHANGES PRODUCED BY HUMAN ACTIVITY ON EXAMPLE OF A KARST LAKE WITH THERMAL SPRING-WATER

Nowadays natural habitats are imperilled because of human landscape-transformer processes and negative effects of climate change. Watery habitats belong to the most vulnerable lands because low rate of anthropogenic effects can lead to significant and fast changes in these places. Although we can characterize Carpatian Basin with high mosaicity, it is need to be managed in its entirety without borders. The international realization of this is supported by the Hungary-Romania Cross-Border Co-operation Programme of the European Union. Conditions of Püspökfürdő (karst lake with thermal spring-water, Pârâul Peţea reserve, Oradea, NW Romania) and anthropogenic effects in dynamics of environmental processes are examined in this project. Paleoecological analysis, soil- and wather-chemical measurements and geological examinations are carried out in the area. Based on laboratory measurements and field studies we are able to do comparative analysis, prepare parameter-maps and examine the evolution of the area. Aims of our work are to classify ecological potential, to define the rate of degradation and to determine ecological function of the natural habitat. Results give possibility to sustainable development of tourism investments and operation in case of Püspökfürdő, what assists the improvement of ecological status of the lake, because Pârâul Peţea reserve is touched by anthropogenic effects in higher degree. In this paper we present a part of examinations of water chemistry