Induced Resistance in Hypersensitive Tobacco Against Tobacco Mosaic Virus by Injection of Intercellular Fluid from Tobacco Plants with Systemic Acquired Resistance

Acquired resistance in hypersensitive tobacco plants against tobacco mosaic virus (TMV) was induced by components occurring in the intercellular fluid (IV) obtained from virus-infected plants or by plant cell wall components. Induced resistance could be transmitted through seed to the progeny. Lesion size and number were reduced significantly when the progeny was tested by TMV-inoculation. IV was extracted from the upper uninoculated leaves of four times TMV-inoculated Nicotiana tabacum cv. ‘Xanthi’ nc plants. Injection of IV from induction-inoculated plants (SAR-IV) into leaves of healthy plants followed by TMV-infection reduced lesion size significantly. A concentration of 5 × 10^?7 g SAR-IV/ml was still active. IV from healthy plants was inactive. The IV's were partly purified by gel filtration on a Sephadex G-50 column. Some fractions were active in inducing resistance as expressed in reduction of lesion size. Fractions of control-IV were inactive. It is still unknown whether the active substances in SAR-IV are in fact cell wall fragments acting as regulatory molecules in disease resistance.     

Acquired Resistance in Hypersensitive Tobacco against Tobacco Mosaic Virus, Induced by Plant Cell Wall Components

Isolated cell walls from Nicotiana tabacum L. cv. Xanthi-nc were partially digested with enzymes present in the fungal preparation cellulase Onozuka R-10. Released carbohydrate material was separated from the enzymes by gel filtration and fractions were injected into the intercellular spaces of one half of each of several Xanthi-nc leaves. Two to three days after injection the whole leaves were inoculated with TMV. A large reduction in mean lesion diameter was observed in the injected areas compared with those in untreated tissue.     

Acquired Resistance in Hypersensitive Tobacco Operates by Limiting Cell-to-Cell Spread of Virus Infection without Affecting Virus Multiplication

Localized and systemic acquired resistance against tobacco mosaic virus (TMV) or tobacco necrosis virus was induced when local lesions were produced in leaves of Xanthi-nc tobacco by mechanical inoculation with TMV. Both types of resistance were characterized by reduction in the size of lesions produced by the challenging viruses, whereas accumulation of viral antigen in lesions was slightly increased. These results, confirming previous findings relative to other hypersensitive plant virus combinations, do not support the view that an inhibitor of virus replication operates in the resistant tissues, but indicate that both types of resistance operate only against cell-to-cell spread of virus.     

The Hypersensitive Reaction of Soybean Cultivars to Tobacco Necrosis Virus Does Not Induce Systemic Resistance but Inhibits Plant Growth

The commercial dry bean (Phaseolus vulgaris L) production system in Alberta requires irrigation and the viny cultivars currently used in this production system are prone to outbreaks of white mold caused by Sclerotinia sderotiorum (Lib.) de Bary. The use of beans with an upright growth habit has potential for alleviating the disease problem, but the narrow profile of the upright beans may warrant a different planting pattern to achieve high yield. A study was undertaken to determine the effect of between- and within-row spacings on the occurrence of white mold and seed yield of upright beans. An experimental navy bean composite with upright growth habit, and a susceptible control Red Mexican, UI 37, were evaluated using three between-row (BR) and three within-row (WR) spacings in presence or absence of white mold during a 2-year period. The BR and WR spacings had no effect (P > 0. 05) on disease occurrence in the inoculated upright composite or in the viny control. Regardless of BR and WR spacings, the upright composite had less (P < 0. 01) disease than the control in both years. In general, large differences (P < 0. 05) were found between the upright composite and control spacing treatments in the presence or absence of white mold. BR spacing had a significant effect on seed yield, but WR spacing did not. In most cases, increasing plant density by reducing BR spacings resulted in higher seed yields. These findings suggest that producers may gain in seed yield without increasing risks for white mold occurrence by changing from viny to upright beans and planting in narrower rows.     

Resistance to Potato Virus X Infection in Transgenic Tobacco Plants with Coat Protein Gene of Virus

A major commercial cultivar of tobacco was transformed via Agrobacterium mediated procedure. Tobacco leaves started to form shoots on shoot inducing medium containing kanamycin after infected by Agrobacterium containing the plasmid with PVX CP gene. Regenerated plants were obtained in two weeks on hormone-free MS medium containing kanamycin. The transgenic tobacco plants were identified with nopaline detection,enzyme-linked immunosorbent assay and western blot analysis, symptom appearance was significantly delayed and virus accumulation was either absent or reduced in PVX CP gene transformed plants. Progenies of transgenic tobacco plants also gained resistance to PVX infection to a certain degree. These experiments demonstrate that CP protection is effective against PVX.     

Two Apoplastic alpha-Amylases Are Induced in Tobacco by Virus Infection

α-Amylase activity (EC 3.2. 1.1) is greatly increased in leaves of tobacco (Nicotiana tabacum L. cv Samsun NN) infected with tobacco mosaic virus (TMV). The kinetics of enzyme induction during the hypersensitive reaction resemble those of other hydrolases known to be pathogenesis-related proteins of tobacco. Two α-amylases were purified from TMV-infected leaves and shown to have features in common with well-characterized pathogenesis-related proteins: they are acidic monomers that can be separated upon electrophoresis on basic native gels, and they are found in the apoplastic compartment of the cell. This extra-cellular localization was demonstrated by comparing the α-amylase partition between the intercellular wash fluid and the cell extract with that of proteins of known cellular compartmentalization. These data indicate an active secretion of both α-amylases produced in tobacco upon TMV infection.     

The Systemic Infection by Tobacco Mosaic Virus of Tobacco Plants Coutaining the N Gene at Temperatures Below 28°C

Tobacco plants containing the N-gene are occasionally systemically infected with tobacco mosaic virus (TMV) at tempreratures below 28°C, but contain low concentrations of virus: they often fail to set seed, and can outlive healthy control plants. Infection is thus similar to that induced when N-gene tobacco plants are grafted onto systemically infected tobacco lacking the N-gene. Shoots from systemically infected N-gene plants can induce systemic infection in other graft-inoculated N-gene plants. Stem sections of N-gene tobacco plants act as good conduits for TMV between plants lacking the N-gene, and girdling experiments suggest that virus movement probably occurs in the phloern.     

Constitutive Expression of Interferon-Induced Human MxA Protein in Transgenic Tobacco Plants Does not Confer Resistance to a Variety of RNA Viruses

MxA is a key component in the interferon-induced antiviral defense in humans. After viral infections, MxA is rapidly induced and accumulates in the cytoplasm. The multiplication of many RNA viruses,including all bunyaviruses tested so far, is inhibited by MxA. These findings prompted us to express MxA in plants in an attempt to create resistance to tospoviruses. Here, we report the generation of transgenic tobacco plants that constitutively express MxA under the control of the 35S cauliflower mosaic virus promotor. Northern and western blot analysis confirmed the expression of MxA in several transgenic plant lines. MxA expression had no obvious detrimental effects on plant growth and fertility. However, challenge experiments with tomato spotted wilt virus, tomato chlorotic spot virus, and groundnut ringspot virus revealed no increased resistance of MxA-transgenic tobacco plants to tospovirus infections. Neither was the multiplicationof tobacco mosaic virus, cucumber mosaic virus and potato virus Y inhibited in MxA-transgenic plants. The results indicate that the expression of human MxA alone does not enhance virus resistance in planta.     

Induced Resistance Against Plasmopara helianthi in Sunflower Plants by DL-β-Amino-n-butyric acid

Sunflower plants treated with the nonprotein amitio add, DL-β-attiino- n -butyric acid (BABA) were protected against infection with Plasmopara helianthi. Soil drenches at the highest rates (150-250 mg/kg soil), applied one day before the inoculation induced high levels of protection (80-83%) against the disease and more than 90% control was observed when BABA was applied at 300 mg/kg soil. However, at this concentration phytotoxic symptoms were observed. This compound also provided a curative activity when applied one day post-inoculation. BABA had no antifungal activity in vitro against P. helianthi. The effect of BABA on zoosporangia germination was evaluated by treating pre-germinated seeds with the compound solution and the zoosporangia suspension for 3 h. Then, seeds were sown and the percentages of infected plants were determined. The other two aminobutyric acid isomers (a and g) were ineffective against downy mildew. The mechanisms by which DL-β-amino- n -butyric acid protect sunflowers against downy mildew awaits more detailed elucidation.     

Hexokinases of Tobacco Leaves: Changes in the Cytosolic and Non-Cytosolic Isozyme Complexes Induced by Tobacco Mosaic Virus Infection

Changes in the cytosotic (soluble) and the non-cytosolic (particulate) isozyme composition of hexokinases and in their properties were studied by ion exchange chromatography on DEAE cellulose after the subcellular fractionation both in the healthy and the tobacco mosaic virus (TMV) infected tobacco leaves. Three main isozyme complexes were obtained: one particulate fraction (the particulate hexokinase phosphorylating both glucose and fructose, EC 2.7.1.1), and two soluble fractions (the soluble hexokinase phosphorylating both the glucose and the fructose, and the soluble fructokinase, which phosphorylates primarily fructose, EC 2.7.1.4). The total fructokinase activities were nearly twice higher than the total glucokinase activities (188.6 % of glucokinase activity in healthy plants and 181.3 % in infected plants). The total particulate glucokinase activity was increased to 120.6 % and the fructokinase to 118.9 % in TMV infected tissue when compared with healthy control. The similar pattern of activity was observed for soluble hexokinase isozymes - the sum of soluble glucokinase activity was increased to 175.4 % and of fructokinase activity to 131.2 % in TMV infected tissue. The isozymes isolated both from the healthy control and TMV-infected leaves had the similar elution profiles, displayed Michaelis-Menten kinetics, showed the identical profiles of pH optima and were Mg²⁺ dependent with the highest enzyme activity at equimolar Mg²⁺ and ATP concentration. This revised version was published online in July 2006 with corrections to the Cover Date.     

Adenovirus Specific Pre-Immunity Induced by Natural Route of Infection Does Not Impair Transduction by Adenoviral Vaccine Vectors in Mice

Recombinant human adenovirus serotype 5 (HAd5V) vectors are gold standards of T-cell immunogenicity as they efficiently induce also humoral responses to exogenous antigens, in particular when used in prime-boost protocols. Some investigators have shown that pre-existing immunity to adenoviruses interferes with transduction by adenoviral vectors, but the actual extent of this interference is not known since it has been mostly studied in mice using unnatural routes of infection and virus doses. Here we studied the effects of HAd5V-specific immune responses induced by intranasal infection on the transduction efficiency of recombinant adenovirus vectors. Of interest, when HAd5V immunity was induced in mice by the natural respiratory route, the pre-existing immunity against HAd5V did not significantly interfere with the B and T-cell immune responses against the transgene products induced after a prime/boost inoculation protocol with a recombinant HAd5V-vector, as measured by ELISA and in vivo cytotoxic T-cell assays, respectively. We also correlated the levels of HAd5V-specific neutralizing antibodies (Ad5NAbs) induced in mice with the levels of Ad5NAb titers found in humans. The data indicate that approximately 60% of the human serum samples tested displayed Ad5NAb levels that could be overcome with a prime-boost vaccination protocol. These results suggest that recombinant HAd5V vectors are potentially useful for prime-boost vaccination strategies, at least when pre-existing immunity against HAd5V is at low or medium levels.     

一氧化氮在寡糖素诱导的小麦对条锈菌系统获得抗性中的时序性

研究了寡糖素在诱导感病小麦品种辉县红系统抗条锈性中的作用,同时利用ESR测定了系统获得抗性（SAR）中一氧化氮(NO)的时间进程,结果表明寡糖素可以诱导辉县红对条锈菌毒性小种CY29-1的系统抗性,此系统抗性与内源NO信号启动的时间及强度有关.     

Tobacco Mosaic Virus Infection Results in an Increase in Recombination Frequency and Resistance to Viral,Bacterial, and Fungal Pathogens in the Progeny of Infected Tobacco Plants

Our previous experiments showed that infection of tobacco (Nicotiana tabacum) plants with Tobacco mosaic virus (TMV) leads to an increase in homologous recombination frequency (HRF). The progeny of infected plants also had an increased rate of rearrangements in resistance gene-like loci. Here, we report that tobacco plants infected with TMV exhibited an increase in HRF in two consecutive generations. Analysis of global genome methylation showed the hypermethylated genome in both generations of plants, whereas analysis of methylation via 5-methyl cytosine antibodies demonstrated both hypomethylation and hypermethylation. Analysis of the response of the progeny of infected plants to TMV, Pseudomonas syringae, or Phytophthora nicotianae revealed a significant delay in symptom development. Infection of these plants with TMV or P. syringae showed higher levels of induction of PATHOGENESIS-RELATED GENE1 gene expression and higher levels of callose deposition. Our experiments suggest that viral infection triggers specific changes in progeny that promote higher levels of HRF at the transgene and higher resistance to stress as compared with the progeny of unstressed plants. However, data reported in these studies do not establish evidence of a link between recombination frequency and stress resistance.Continuous exposure to stress leads to the evolutionary selection of adaptive traits beneficial in a particular environment. Such selection of the fittest of a population of plants grown under certain environmental conditions is believed to require a long time. However, it is known that plants also possess the ability to acclimate on much shorter time scales. A modification of homeostasis, also termed acclimatization, is a well-documented process that is used for adjusting metabolism to a new environment (Lichtenthaler, 1998; Mullineaux and Emlyn-Jones, 2005).Pathogens represent one of a variety of stresses that plants are constantly exposed to. In nature, the evolution of plant resistance to a particular pathogen, virus, bacterium, or fungus has been the result of constant interactions with said pathogen (McHale et al., 2006; Friedman and Baker, 2007). These interactions lead to a constant plant-pathogen arms race (Ingle et al., 2006).Plants are able to tolerate or resist pathogens in a variety of ways, which could be broadly attributed to mechanisms of innate immunity and actual gene-for-gene-based resistance. The latter one depends on direct or indirect recognition of pathogen avirulence gene products by plant resistance gene products (Whitham et al., 1994; Durrant and Dong, 2004). Pathogen recognition during this incompatible interaction triggers complex events, including a local hypersensitive response that manifests itself as a booster of radical production and activation of the salicylic acid-dependent pathway and necrotic lesions, which working together restrict pathogen spread. It also results in a plant-wide systemic acquired resistance response that provides protection and tolerance to future pathogen attacks (Durrant and Dong, 2004; Park et al., 2007; Vlot et al., 2008).If a functional pathogen resistance gene is absent (compatible interaction), then the interaction between a plant and a pathogen is more ambiguous. How do plants that lack a resistance gene respond to infection? We have previously reported that the compatible interaction between Tobacco mosaic virus (TMV) and tobacco (Nicotiana tabacum ‘SR1’) plants lacking the TMV resistance N gene results in the production of a systemic signal. The signal leads to an increase in the frequency of somatic homologous recombination (HRF; Kovalchuk et al., 2003a). Based on these observations, we hypothesized that these genomic changes could be inherited. Indeed, we found that the progeny of infected SR1 tobacco plants exhibited a higher frequency of RFLPs at the loci that have similarity (more than 60%) to the Leu-rich repeat region of the N gene (Boyko et al., 2007).Although several reports have shown an increase in genome instability in plants exposed to pathogens and pathogen elicitors (Lucht et al., 2002; Kovalchuk et al., 2003a; Molinier et al., 2006; Boyko et al., 2007), many questions still remained unanswered. What is the mechanism of occurrence of a pathogen-induced systemic increase in HRF? What is the mechanism of inheritance of high-frequency homologous recombination? Are elevated levels of HRF maintained throughout generations? What other changes occur in progeny of infected plants?Here, we attempted to answer the above questions by analyzing two consecutive progenies of TMV-infected tobacco cv SR1 plants. Both progenies of infected plants showed higher levels of somatic HRF, higher resistance to TMV infection and tolerance to methyl methane sulfonate (MMS), an increase in callose deposition, as well as a higher steady-state PATHOGENESIS-RELATED GENE1 (PR1) RNA level compared with the progeny of uninfected plants. Analysis of methylation patterns has revealed global genome hypermethylation in both progenies paralleled by hypomethylation in euchromatic areas.     

Induced Systemic Resistance Against Sphaerotheca fuliginea in Cucumber: Efficiency of Tobacco Necrosis Virus (TNV) and Copper Sulphate (CuSO4) in Eliciting Defence Reactions

Plants of Cucumis sativus were eithe preinoculated with TNV or treated with drops of a 5% solution of CuSO₄ on the cotyledons, and 5 days later challenge-inoculated with Sphaerotheca fuliginea on the first true leaf. The induced systemic resistance was assessed by evaluating the percentage of conidial germination, the length of the hyphae derived from single conidia, the number of cells with lignified walls and that of cells containing haustoria. The number of necrotic cells was also recorded. Compared with controls, in TNV-preinoculated plants conidial germination was lower, hyphal length shorter and the number of haustoria much reduced. The majority of haustoria was found in cells with lignified walls. Pretreatment with CuSO₄, although inducing a slight increase of cell wall lignification, did not appreciably reduce the infection process. The number of necrotic cells was very low in all cases. These results suggest that, in this host/pathogen interaction, hypersensitive cell death has no part in the induced defence reaction, although a major role is played by the lignification process.     

Systemic Induction of Resistance in Potato Plants Against Phytophthora infestans by Local Treatment with Hyphal Wall Components of the Fungus

Potato plants (cv.‘Irish Cobbler’ with no major resistance genes to Phytophthora infestans), the lower or upper leaves of which were previously treated with hyphal wall components (HWC) of the fungus by rubbing with carborundum, acquired an induced resistance in other untreated leaves against cultivar-pathogenic races of P. infestans when challenged by spraying with a zoospore suspension. Such induced resistance was significantly shown to exist from at least 1 to 20 days after induction treatment with HWC. Thus, the treated plants were protected from severe late blight disease while non-induced control plants finally died of the disease. The induced resistance was due to a reduction of the number of successfully germinating zoospores, and subsequent penetration and then occurrence of hypersensitive-like cell response to the penetrating organisms. These results suggested that local leaf tissues of potato plants reacting to HWC may provide some systemic information that activates or enhances some resistance to P. infestans.