Induction of tomato stress protein mRNAs by ethephon, 2,6-dichloroisonicotinic acid and salicylate

To study the possible involvement of plant hormones in the synthesis of stress proteins in tomato upon inoculation with Cladosporium fulvum, we investigated the induction of mRNAs encoding PR proteins and ethylene biosynthesis enzymes by ethephon, 2,6-dichloroisonicotinic acid (INA) and salicylic acid (SA) by northern blot analysis. Ethephon slightly induced some but not all mRNAs encoding intra- and extracellular PR proteins. INA induced all PR protein mRNAs analysed, except for intracellular chitinase and extracellular PR-4. SA induced all PR protein mRNAs analyzed, except for intracellular chitinase and osmotin. None of the inducers affected the expression of ACC synthase mRNA, whereas all three induced ethylene-forming enzyme (EFE) mRNA.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - EFE ethylene-forming enzyme - HR hypersensitive response - INA 2,6-dichloroisonicotinic acid - PR pathogenesis-related - SA salicylic acid - SAR systemic acquired resistance     

外源Ca2+对水杨酸诱导番茄抗灰霉病的增效机制

探讨了外源Ca²⁺对水杨酸(SA)诱导番茄抗灰霉病的增效机制.以番茄灰霉病敏感型品种‘L402’幼苗为材料,分别进行H₂O(对照)、SA、SA+Ca和SA+EGTA(Ca²⁺螯合剂)处理,期间(1～5 d)分析各处理植株叶片活性氧(ROS)含量,苯丙氨酸解氨酶、几丁质酶和β-1,3-葡聚糖酶活性,以及病程相关蛋白编码基因PR1、PR2和PR3表达水平的变化,并调查处理3 d后灰霉病情指数.结果表明： 与对照(病情指数为74.8)相比,SA、SA+Ca和SA+EGTA处理的植株叶片灰霉病的病情指数分别为46.9、38.5和70.3;SA处理明显提高叶片ROS含量以及苯丙氨酸解氨酶、几丁质酶和β-1,3-葡聚糖酶活性,这些参数在SA+Ca处理的植株中被进一步提高,但在SA+EGTA处理的植株中则被降低;SA处理明显提高了PR1、PR2a和PR3b的表达水平,Ca²⁺进一步加强了这一效果,而EGTA则起抑制作用.SA或SA+Ca处理期间的PR2b和PR3a表达较未处理的对照上调了1～2倍,而PR1、PR2a和PR3b上调了2～5倍.表明Ca²⁺对SA诱导番茄抗灰霉病具有增效作用,其机理至少与Ca²⁺和SA协同作用促进ROS形成有关,而ROS作为信号分子增加植株抗病相关酶活性以及PR1、PR2a和PR3b等防卫基因的表达.     

外源Ca2+对水杨酸诱导番茄抗灰霉病的增效机制

探讨了外源Ca²⁺对水杨酸(SA)诱导番茄抗灰霉病的增效机制.以番茄灰霉病敏感型品种‘L402’幼苗为材料,分别进行H₂O(对照)、SA、SA+Ca和SA+EGTA(Ca²⁺螯合剂)处理,期间(1～5 d)分析各处理植株叶片活性氧(ROS)含量,苯丙氨酸解氨酶、几丁质酶和β-1,3-葡聚糖酶活性,以及病程相关蛋白编码基因PR1、PR2和PR3表达水平的变化,并调查处理3 d后灰霉病情指数.结果表明： 与对照(病情指数为74.8)相比,SA、SA+Ca和SA+EGTA处理的植株叶片灰霉病的病情指数分别为46.9、38.5和70.3;SA处理明显提高叶片ROS含量以及苯丙氨酸解氨酶、几丁质酶和β-1,3-葡聚糖酶活性,这些参数在SA+Ca处理的植株中被进一步提高,但在SA+EGTA处理的植株中则被降低;SA处理明显提高了PR1、PR2a和PR3b的表达水平,Ca²⁺进一步加强了这一效果,而EGTA则起抑制作用.SA或SA+Ca处理期间的PR2b和PR3a表达较未处理的对照上调了1～2倍,而PR1、PR2a和PR3b上调了2～5倍.表明Ca²⁺对SA诱导番茄抗灰霉病具有增效作用,其机理至少与Ca²⁺和SA协同作用促进ROS形成有关,而ROS作为信号分子增加植株抗病相关酶活性以及PR1、PR2a和PR3b等防卫基因的表达.     

Arabidopsis local resistance to Botrytis cinerea involves salicylic acid and camalexin and requires EDS4 and PAD2, but not SID2, EDS5 or PAD4

Salicylic acid (SA) is an important regulator of plant defense responses, and a variety of Arabidopsis mutants impaired in resistance against bacterial and fungal pathogens show defects in SA accumulation, perception, or signal transduction. Nevertheless, the role of SA-dependent defense responses against necrotrophic fungi is currently unclear. We determined the susceptibility of a set of previously identified Arabidopsis mutants impaired in defense responses to the necrotrophic fungal pathogen Botrytis cinerea. The rate of development of B. cinerea disease symptoms on primary infected leaves was affected by responses mediated by the genes EIN2, JAR1, EDS4, PAD2, and PAD3, but was largely independent of EDS5, SID2/ICS1, and PAD4. Furthermore, plants expressing a nahG transgene or treated with a phenylalanine ammonia lyase (PAL) inhibitor showed enhanced symptoms, suggesting that SA synthesized via PAL, and not via isochorismate synthase (ICS), mediates lesion development. In addition, the degree of lesion development did not correlate with defensin or PR1 expression, although it was partially dependent upon camalexin accumulation. Although npr1 mutant leaves were normally susceptible to B. cinerea infection, a double ein2 npr1 mutant was significantly more susceptible than ein2 plants, and exogenous application of SA decreased B. cinerea lesion size through an NPR1-dependent mechanism that could be mimicked by the cpr1 mutation. These data indicate that local resistance to B. cinerea requires ethylene-, jasmonate-, and SA-mediated signaling, that the SA affecting this resistance does not require ICS1 and is likely synthesized via PAL, and that camalexin limits lesion development.     

Nitric oxide and hydrogen peroxide in tomato resistance. Nitric oxide modulates hydrogen peroxide level in o-hydroxyethylorutin-induced resistance to Botrytis cinerea in tomato.

Nitric oxide (NO) has been postulated to be required, together with reactive oxygen species (ROS), for activation of disease resistance reactions of plants to infection with a pathogen or elicitor treatment. However, biochemical mechanisms by which ROS and NO participate in these reactions are still under intensive study and controversial debate. We previously demonstrated that o-hydroxyethylorutin when applied on tomato leaves (Lycopersicon esculentum Mill. cv. "Perkoz") restricted Botrytis cinerea infection development. In this research we investigated ROS and NO generation in tomato plants treated with o-hydroxyethylorutin, non-treated and infected ones. The NO content was enhanced or decreased in the studied plants by supplying them with NO generator-SNP or scavenger-cPTIO. NO detection was carried out using diaminofluorescein diacetate (DAF-DA) in conjunction with confocal laser scanning microscopy. The influence of elevated and decreased levels of NO on B. cinerea infection development and ROS generation was studied. The elevated NO concentration in tomato leaves strongly decreased hydrogen peroxide concentration without affecting other studied ROS (superoxide anion and hydroxyl radical) levels. H2O2 concentrations in NO-supplied leaves were low regardless of further treatment of tomato leaves with o-hydroxyethylorutin or inoculation with B. cinerea. The low H2O2 concentration coincided with quick and severe infection development in NO-supplied leaves. As activities of enzymes generating (SOD EC 1.15.1.1)) and removing (APX EC 1.11.1.11, CAT EC 1.11.1.6) H2O2 were unchanged in the studied plants, the decrease in H2O2 concentration was probably due to a direct NO-H2O2 interaction.     

Characterization of an Arabidopsis Mutant That Is Nonresponsive to Inducers of Systemic Acquired Resistance

Systemic acquired resistance (SAR) is a general defense response in plants that is characterized by the expression of pathogenesis-related (PR) genes. SAR can be induced after a hypersensitive response to an avirulent pathogen or by treatment with either salicylic acid (SA) or 2,6-dichloroisonicotinic acid (INA). To dissect the signal transduction pathway of SAR, we isolated an Arabidopsis mutant that lacks the expression of an SA-, INA-, and pathogen-responsive chimeric reporter gene composed of the 5[prime] untranslated region of an Arabidopsis PR gene, [beta]-1,3-glucanase (BGL2), and the coding region of [beta]-glucuronidase (GUS). This mutant, npr1 (nonexpresser of PR genes), carries a single recessive mutation that abolishes the SAR-responsive expression of other PR genes as well. While SA-, INA-, or avirulent pathogen-induced SAR protects wild-type plants from Pseudomonas syringae infection, the mutant cannot be protected by pretreatment with these inducers. The insensitivity of npr1 to SA, INA, and avirulent pathogens in SAR induction indicates that these inducers share a common signal transduction pathway. Moreover, in npr1, the localized expression of PR genes induced by a virulent Pseudomonas pathogen is disrupted, and the lesion formed is less confined. These results suggest a role for PR genes in preventing the proximal spread of pathogens in addition to their suggested role in SAR.     

两种葡萄孢属真菌对不同品种百合花瓣和叶片的侵染能力比较

为明确两种葡萄孢属真菌对不同百合品种叶片和花瓣的侵染能力,采用离体叶片接种法测定灰葡萄孢Botrytis cinerea和椭圆葡萄孢Botrytis elliptica对4个百合品种叶片和花瓣的侵染时间和病斑扩展速度。结果表明,供试百合花瓣接种灰葡萄孢病斑出现时间明显早于叶片,而不同品种花瓣接种椭圆葡萄孢病斑出现时间差异显著。此外,百合品种‘木门’叶片接种椭圆葡萄孢96 h后仍没有病斑出现,而花瓣接种后48 h病斑出现,说明‘木门’叶片对椭圆葡萄孢抗性较强,而花瓣较易感病。     

Tobacco plants epigenetically suppressed in phenylalanine ammonia-lyase expression do not develop systemic acquired resistance in response to infection by tobacco mosaic virus

The response of tobacco (Nicotiana tabacum L. cv. Xanthinc) plants, epigenetically suppressed for phenylalanine ammonia-lyase (PAL) activity, was studied following infection by tobacco mosaic virus (TMV). These plants contain a bean PAL2 transgene in the sense orientation, and have reduced endogenous tobacco PAL mRNA and suppressed production of phenylpropanoid products. Lesions induced by TMV infection of PAL-suppressed plants are markedly different in appearance from those induced on control plants that have lost the bean transgene through segregation, with a reduced deposition of phenofics. However, they develop at the same rate as on control tobacco, and pathogenesis-related (PR) proteins are induced normally upon primary infection. The levels of free salicylic acid (SA) produced in primary inoculated leaves of PAL-suppressed plants are approximately fourfold lower than in control plants after 84 h, and a similar reduction is observed in systemic leaves. PR proteins are not induced in systemic leaves of PAL-suppressed plants, and secondary infection with TMV does not result in the restriction of lesion size and number seen in control plants undergoing systemic acquired resistance (SAR). In grafting experiments between wild-type and PAL-suppressed tobacco, the SAR response can be transmitted from a PAL-suppressed root-stock, but SAR is not observed if the scion is PAL-suppressed. This indicates that, even if SA is the systemic signal for establishment of SAR, the amount of pre-existing phenylpropanoid compounds in systemic leaves, or the ability to synthesize further phenylpropanoids in response to the systemic signal, may be important for the establishment of SAR. Treatment of PAL-suppressed plants with dichloro-isonicotinic acid (INA) induces PR protein expression and SAR against subsequent TMV infection. However, treatment with SA, while inducing PR proteins, only partially restores SAR, further suggesting that de novo synthesis of SA, and/or the presence or synthesis of other phenylpropanoids, is required for expression of resistance in systemic leaves.     

Marker Gene Overexpression in Flowers Treated with Resistance Inducers does not Correlate with Protection Against Flower‐Infecting Fungi in Tomato and Blueberry

Flowers can serve as infection courts for specialized and unspecialized plant pathogens, but little is known about the ability of floral tissues to undergo induced resistance (IR) responses against these pathogens. We studied the expression of IR marker genes in tomato and blueberry flowers treated with the inducers methyl jasmonate (MeJA), benzothiadiazole‐S‐methyl ester (BTH) and 2,6‐dichloroisonicotinic acid (INA). In tomato, spray application of MeJA and BTH (but not INA) to entire plants (leaves, stems and flowers) resulted in a significant (P < 0.05) overexpression of Pin2 (5.2‐fold) and PR‐4 (5.6‐fold) in pistil tissues, respectively. A statistically similar expression was obtained in pistils when flowers were protected from direct spray, indicating a systemic response. In blueberry, where information about IR marker genes is limited, PR‐3 and PR‐4 orthologs were first identified and characterized using in silico and wet‐laboratory techniques. In subsequent induction experiments, INA and BTH induced overexpression of PR‐4 in blueberry pistils by 3.2‐ and 1.8‐fold, respectively, when entire plants were treated. In blueberry flowers protected from spray applications, all chemicals applied to vegetative tissues led to significant overexpression of PR‐4 (MeJA: 1.4‐fold, BTH: 2.9‐fold and INA: 1.6‐fold), with BTH also inducing PR‐3 (1.7‐fold). The effect of these responses in protecting flowers was studied by inoculating treated tomato flowers with the necrotroph Botrytis cinerea and blueberry flowers with the hemi‐biotroph Monilinia vaccinii‐corymbosi. In both pathosystems, no significant disease suppression associated with resistance inducer application was observed under the conditions studied. Thus, although IR marker genes were shown to be inducible in floral tissue, the magnitude of this response was insufficient to suppress pathogen ingress.     

Local and systemic protection of poinsettia (Euphorbia pulcherrima Willd.) against Botrytis cinerea Pers. induced by benzothiadiazole

Benzothiadiazole (BTH) was found to be highly effective in increasing resistance of two poinsettia cultivars — ‘Coco White’ and ‘Malibu Red’, moderately susceptible to the fungus Botrytis cinerea. BTH applied at a concentration of 0.3 mM on the discs cut out from the leaves of these poinsettia cultivars reduced disease symptoms by more than 60 % in comparison to the control discs treated with water and exposed to infection. It was also observed that the applied inducer at a concentration of 0.03 and 0.3 mM had a favourable influence on the increase of poinsettia systemic resistance of SAR type (systemic acquired resistance). The effectiveness of BTH was much less when disease development was examined on detached leaves (a 20 % reduction of lesion area) in comparison with a pronounced inhibition of grey mould development on intact leaves of previously induced plants (a 80 % protection of intact plants). Benzothiadiazole in the concentration range from 0.03 to 1.4 mM added to in vitro agar medium was not found to have an inhibitory influence on Botrytis cinerea mycelium growth and sporulation.     

Wounding of Arabidopsis leaves causes a powerful but transient protection against Botrytis infection

Physical injury inflicted on living tissue makes it vulnerable to invasion by pathogens. Wounding of Arabidopsis thaliana leaves, however, does not conform to this concept and leads to immunity to Botrytis cinerea , the causal agent of grey mould. In wounded leaves, hyphal growth was strongly inhibited compared to unwounded controls. Wound-induced resistance was not associated with salicylic acid-, jasmonic acid- or ethylene-dependent defence responses. The phytoalexin camalexin was found to be involved in this defence response as camalexin-deficient mutants were not protected after wounding and the B. cinerea strains used here were sensitive to this compound. Wounding alone did not lead to camalexin production but primed its accumulation after inoculation with B. cinerea , further supporting the role of camalexin in wound-induced resistance. In parallel with increased camalexin production, genes involved in the biosynthesis of camalexin were induced faster in wounded and infected plants in comparison with unwounded and infected plants. Glutathione was also found to be required for resistance, as mutants deficient in γ-glutamylcysteine synthetase showed susceptibility to B. cinerea after wounding, indicating that wild-type basal levels of glutathione are required for the wound-induced resistance. Furthermore, expression of the gene encoding glutathione- S -transferase 1 was primed by wounding in leaves inoculated with B. cinerea . In addition, the priming of MAP kinase activity was observed after inoculation of wounded leaves with B . cinerea compared to unwounded inoculated controls. Our results demonstrate how abiotic stress can induce immunity to virulent strains of B. cinerea , a process that involves camalexin and glutathione.     

A benzothiadiazole derivative induces systemic acquired resistance in tobacco

Systemic acquired resistance (SAR) is a pathogen-induced disease resistance response in plants that is characterized by broad spectrum disease control and an associated coordinate expression of a set of SAR genes. Benzo(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH) is a novel synthetic chemical capable of inducing disease resistance in a number of dicotyledenous and monocotyledenous plant species. In this report, the response of tobacco plants to BTH treatment is characterized and the fact that it controls disease by activating SAR is demonstrated. BTH does not cause an accumulation of salicylic acid (SA), an intermediate in the SAR signal transduction pathway. As BTH also induces disease resistance and gene expression in transgenic plants expressing the nahG gene, it appears to activate the SAR signal transduction pathway at the site of or downstream of SA accumulation. BTH, SA and TMV induce the PR-1a promoter using similar cis-acting elements and gene expression is blocked by cycloheximide treatment. Thus, BTH induces SAR based on all of the physiological and biochemical criteria that define SAR in tobacco.     

Induction of a new Lipoxygenase Form in Cucumber Leaves by Salicylic Acid or 2,6-Dichloroisonicotinic Acid*

Changes in lipoxygenase (LOX) protein pattern and/or activity were investigated in relation to acquired resistance of cucumber (Cucumis sativus L.) leaves against two powdery mildews, Sphaerotheca fuliginea (Schlecht) Salmon and Erysiphe cichoracearum DC et Merat. Acquired resistance was established by spraying leaves with salicylic acid (SA) or 2,6-dichloroisonicotinic acid (INA) and estimated in whole plants by infested leaf area compared to control plants. SA was more effective than INA. According to Western blots, untreated cucumber leaves contained a 97 kDa LOX form, which remained unchanged for up to 48 h after pathogen inoculation. Upon treatment with SA alone for 24 h or with INA plus pathogen, an additional 95 kDa LOX form appeared which had an isoelectric point in the alkaline range. For the induction of this form, a threshold concentration of 1 mM SA was required, higher SA concentrations did not change LOX-95 expression which remained similar between 24 h and 96 h but further increased upon mildew inoculation. Phloem exudates contained only the LOX-97 form, in intercellular washing fluid no LOX was detected. dichloroisonicotinic localization revealed LOX protein in the cytosol of the mesophyll cells without differences between the forms.     

Application of benzothiadiazole and Trichoderma harzianum to control faba bean chocolate spot disease and their effect on some physiological and biochemical traits

Chocolate spot disease is the most prevalent and important disease in the major faba bean growing regions in the world. Different concentrations of the abiotic inducer (0.3 and 0.5 mM benzothiadiazole) and the biotic inducer (1 × 10⁷ and 2 × 10⁷ spore/ml Trichoderma harzianum) were used alone or in combination to study their efficiency against faba bean chocolate spot disease caused by Botrytis fabae and Botrytis cinerea and their effect on some chemical analyses (phenylalanine ammonia lyase activity, total flavonoids and peroxidase isozymes, pectin and lignin content and total chlorophyll content). Application of the tested inducers as foliar treatment significantly reduced the severity of chocolate spot disease as compared with untreated infected plants. The reduction in disease severity was associated with a gradual increase in phenylalanine ammonia lyase activity. Maximum increase was recorded at 72 h after inoculation with B. fabae and B. cinerea. In addition, the levels of flavonoids in induced infected leaves recorded a sharp increase at 24 h after inoculation with B. fabae or B. cinerea. Also, pectin and lignin contents in the cell wall of induced infected plants were significantly increased as compared with untreated infected plants. Beside the induction of resistance, the tested inducers markedly increased total chlorophyll content in treated infected plants as compared with untreated infected plants. Isozymes analysis revealed that new peroxidase bands were induced only in treated faba bean leaves in response to infection with B. fabae or B. cinerea.     

Arabidopsis ssi2-conferred susceptibility to Botrytis cinerea is dependent on EDS5 and PAD4

Loss of a stearoyl-ACP desaturase activity in the Arabidopsis thaliana ssi2 mutant confers susceptibility to the necrotroph, Botrytis cinerea. In contrast, the ssi2 mutant exhibits enhanced resistance to Pseudomonas syringae, Peronospora parasitica, and Cucumber mosaic virus. The altered basal resistance to these pathogens in the ssi2 mutant plant is accompanied by the constitutive accumulation of elevated salicylic acid (SA) level and expression of the pathogenesis-related 1 (PR1) gene, the inability of jasmonic acid (JA) to activate expression of the defensin gene, PDF1.2, and the spontaneous death of cells. Here, we show that presence of the eds5 and pad4 mutant alleles compromises the ssi2-conferred resistance to Pseudomonas syringae pv. maculicola. In contrast, resistance to B. cinerea was restored in the ssi2 eds5 and ssi2 pad4 double-mutant plants. However, resistance to B. cinerea was not accompanied by the restoration of JA responsiveness in the ssi2 eds5 and ssi2 pad4 plants. The ssi2 eds5 and ssi2 pad4 plants retain the ssi2-conferred spontaneous cell death phenotype, suggesting that cell death is not a major factor that predisposes the ssi2 mutant to infection by B. cinerea. Furthermore, the high SA content of the ssi2 pad4 plant, combined with our previous observation that the SA-deficient ssi2 nahG plant succumbs to infection by B. cinerea, suggests that elevated SA level does not have a causal role in the ssi2-conferred susceptibility to B. cinerea. Our results suggest that interaction between an SSI2-dependent factor or factors and an EDS5- and PAD4-dependent mechanism or mechanisms modulates defense to B. cinerea.     

Resistance to Botrytis cinerea induced in Arabidopsis by elicitors is independent of salicylic acid, ethylene, or jasmonate signaling but requires PHYTOALEXIN DEFICIENT3

Oligogalacturonides (OGs) released from plant cell walls by pathogen polygalacturonases induce a variety of host defense responses. Here we show that in Arabidopsis (Arabidopsis thaliana), OGs increase resistance to the necrotrophic fungal pathogen Botrytis cinerea independently of jasmonate (JA)-, salicylic acid (SA)-, and ethylene (ET)-mediated signaling. Microarray analysis showed that about 50% of the genes regulated by OGs, including genes encoding enzymes involved in secondary metabolism, show a similar change of expression during B. cinerea infection. In particular, expression of PHYTOALEXIN DEFICIENT3 (PAD3) is strongly up-regulated by both OGs and infection independently of SA, JA, and ET. OG treatments do not enhance resistance to B. cinerea in the pad3 mutant or in underinducer after pathogen and stress1, a mutant with severely impaired PAD3 expression in response to OGs. Similarly to OGs, the bacterial flagellin peptide elicitor flg22 also enhanced resistance to B. cinerea in a PAD3-dependent manner, independently of SA, JA, and ET. This work suggests, therefore, that elicitors released from the cell wall during pathogen infection contribute to basal resistance against fungal pathogens through a signaling pathway also activated by pathogen-associated molecular pattern molecules.     

Is Salicylic Acid a Translocated Signal of Systemic Acquired Resistance in Tobacco?

Salicylic acid (SA) is a likely endogenous signal in the development of systemic acquired resistance (SAR) in some dicotyledonous plants. In tobacco mosaic virus (TMV)-resistant Xanthi-nc tobacco, SA levels increase systemically following the inoculation of a single leaf with TMV. To determine the extent to which systemic increases in SA result from SA export from the inoculated leaf, SA produced in TMV-inoculated or healthy leaves was noninvasively labeled with 18O2. Spatial and temporal distribution of 18O-SA indicated that most of the SA detected in the healthy tissues was synthesized in the inoculated leaf. No significant increase in the activity of benzoic acid 2-hydroxylase, the last enzyme involved in SA biosynthesis, was detected in upper uninoculated leaves, although the basal level of enzyme activity was relatively high. No increases in SA level, pathogenesis-related PR-1 gene expression, or TMV resistance in the upper uninoculated leaf were observed if the TMV-inoculated leaf was detached up to 60 hr after inoculation. Apart from the inoculated tissues, the highest increase in SA was observed in the leaf located directly above the inoculated leaf. The systemic SA increase observed during SAR may be explained by phloem transport of SA from the inoculation sites.     

Malus hupehensis NPR1 induces pathogenesis-related protein gene expression in transgenic tobacco

Most commercially grown apple cultivars are susceptible to fungal diseases. Malus hupehensis has high resistance to many diseases affecting apple cultivars. Understanding innate defence mechanisms would help to develop disease-resistant apple crops. Non-expressor of pathogenesis-related genes 1 (NPR1) plays a key role in regulating salicylic acid (SA)-mediated systemic acquired resistance (SAR). MhNPR1 cDNA, corresponding to genomic DNA and its 5' flanking sequences, was isolated from M. hupehensis. Sequence analysis showed that the regulatory mechanism for oligomer-monomer transition of the MhNPR1 protein in apple might be similar to that of GmNPR1 in soybean, but different from that of AtNPR1 in Arabidopsis. No significant differences in MhNPR1 expression were found in M. hupehensis after infection with Botryosphaeria berengeriana, showing that MhNPR1 might be regulated by pathogens at the protein level, as described for Arabidopsis and grapevine. SA treatment significantly induced MhNPR1 expression in leaves, stems and roots, while methyl jasmonate (MeJA) treatment induced MhNPR1 expression in roots, but not in leaves or stems. The expression of MhNPR1 was highly increased in roots, moderately in leaves, and did not change in stems after treatment with 1-aminocyclopropane-1-carboxylic acid (ACC). SAR marker genes (MhPR1 and MhPR5) were induced by SA, MeJA and ACC in leaves, stems and roots. Overexpression of MhNPR1 significantly induced the expression of pathogenesis-related genes (NtPR1, NtPR3 and NtPR5) in transgenic tobacco plants and resistance to the fungus Botrytis cinerea, suggesting that MhNPR1 orthologues are a component of the SA defence signalling pathway and SAR is induced in M. hupehensis.     

Chitinase and peroxidase activities in sunflower hypocotyls: Effects of BTH and inoculation with <Emphasis Type="Italic">Plasmopara halstedii</Emphasis>

Systemic acquired resistance (SAR) can be induced in plants by incompatible pathogens, pathogen derived extracts, or certain chemicals as benzothiadiazole (BTH). The aim of this work was to compare changes in peroxidase and chitinase activities, enzymes considered as PR-proteins, caused by BTH and the pathogen Plasmopara halstedii. Hypocotyls from susceptible and resistant BTH-treated sunflower seedlings showed increased peroxidase and chitinase activities. Inoculation with P. halstedii increased chitinase and peroxidase activities in inoculated hypocotyls from susceptible but not from resistant sunflower seedlings.