Effects of Exogenous Salicylic Acid Derivative on the Resistance to TMV and Activity of Defense Enzymes of Tobacco

[Objective] This study aimed to evaluate the effects of exogenous salicylic acid derivatives on tobacco resistance to TMV and activity of defense enzymes. [Method] The tobboco leaves were treated by exogenous salicylic acid derivatives. Then, the disease occurrence was observed, and the activity of phenylalanin ammo- nia lyase （PAL） and peroxidase （POX） were measured. [Result] Exogenous salicylic acid derivative increased the activities of PAL and POX, while did not influence the resistance to TMV. [Conclusion] The result provides a theoretical basis for the study of plant disease resistance mechanisms.

Salicylic acid-mediated plant defense： Recent developments, missing links, and future outlook

BACKGROUND： Plant pathogens are responsible for many of history＇s greatest famines. Understanding how plants defend themselves against pathogens is crucial to preventing future famines. Salicylic acid （SA）-mediated plant defense is a key defense pathway, which plants use to defend against biotrophic and hemi-biotrophic pathogens. As a master regulator of SA- mediated plant defense, NPR1 interacts with TGA and WRKY transcription factor families, individual members of which positively or negatively regulate plant defense. OBJECTIVE： In this review we describe the recent developments and predict future directions of research on the involvement of circadian rhythm-, autophagy-, and viral RNA silencing-related genes in SA-mediated plant defense on SA, on plant defense, the induction effects of PR proteins, and the mechanisms by which NPR1 regulates defense-related genes. METHODS： We performed an extensive search of current and past literature using the PubMed, Google Scholar, and Google search engines. Our search terms included： ＂SA-mediated plant defense,＂ and ＂NPR1 [AND] salicylic acid.＂ Other search terms, wildcards, and Boolean operators were paired with ＂NPRI＂ or ＂plant defense＂ as needed to research more detailed information related to specific topics covered within this review. We also used Google to search for, ＂economic impact citrus greening,＂ ＂aspirin,＂ ＂Irish potato famine,＂ and ＂rice blast,＂ among other terms, to gather background information on the history and impact of plant diseases, and the historical use of aspirin. RESULTS： Of 148 sources found, 132 were directly related to plant defense. The remaining sources are related to the historical and economic impact of plant diseases and the historical use and mechanism of action of aspirin or salicylate. All reviewed sources have been documented in the references section. CONCLUSION： The topic of salicylic acid-mediated plant defense is broad, and new research is expanding our understanding of this topic quickly. In this review, we give a basic overview of the historical economic impact of plant diseases, and how an understanding of SA-mediated plant defense can prevent future famines. We provide a basic overview of plant defense, then discuss how SA acts as a defense signaling molecule.We discuss how SA regulates NPR1, which goes on to activate expression of SA-related genes including PR genes. Later, we discuss current research topics, including the role of NPR1 and SA in autophagy, circadian rhythmicity, viral gene silencing, SA biosynthesis, and SAR. We also discuss the potential roles of PR proteins, other SA binding proteins, WRKY and TGA family transcription factors, Elongator, and ER transport proteins in plant defense. Finally, we discuss the potential future routes that research into this topic could take, in order to further our understanding of role SA plays in plant defense.

In vitro and in silico studies of salicylic acid on systemic induced resistance against bacterial leaf blight disease and enhancement of crop yield

Salicylic acid(SA)is an effective elicitor to promote plant defenses and growth.This study aimed to investigate rice(Oryza sativa L.)cv.Khao Dawk Mali 105 treated with salicylic acid(SA)-Ricemate as an enhanced plant protection mechanism against bacterial leaf blight(BLB)disease caused by Xanthomonas oryzae pv.oryzae(Xoo).Results indicated that the use of SA-Ricemate as a foliar spray at concentrations of more than 100 mg L^(-1)can reduce the severity of BLB disease by 71%.SA-Ricemate treatment also increased the hydrogen peroxide(H_(2)O_(2))content of rice leaf tissues over untreated samples by 39–61%.Malondialdehyde(MDA)in rice leaves treated with SA-Ricemate also showed an increase of 50–65%when comparing to non-treated samples.The differential development of these defense compounds was faster and distinct when the SA-Ricemate-treated rice was infected with Xoo,indicating plant-induced resistance.Besides,SA-Ricemate elicitor at a concentration of 50–250 mg L^(-1)was correlated with a substantial increase in the accumulation of total chlorophyll content at 2.53–2.73 mg g^(-1)of fresh weight which suggests that plant growth is activated by SA-Ricemate.The catalase-and aldehyde dehydrogenase-binding sites were searched for using the CASTp server,and the findings were compared to the template.Chemsketch was used to design and optimize SA,which was then docked to the catalase and aldehyde dehydrogenase-binding domains of the enzymes using the GOLD 3.0.1 Software.SA is shown in several docked conformations with the enzymes catalase and aldehyde dehydrogenase.All three catalase amino acids(GLN7,VAL27,and GLU38)were discovered to be involved in the creation of a strong hydrogen bond with SA when SA was present.In this mechanism,the aldehyde dehydrogenase amino acids LYS5,HIS6,and ASP2 were all implicated,and these amino acids created strong hydrogen bonds with SA.In field conditions,SA-Ricemate significantly reduced disease severity by 78%and the total grain yield was significantly increased which was an increase of plant height,tiller per hill,and panicle in three field trials during Aug–Nov 2017 and 2018.Therefore,SA-Ricemate can be used as an alternative elicitor on replacing harmful pesticides to control BLB disease with a high potential of increasing rice defenses,growth,and yield components.

Salicylic Acid Application Mitigates Oxidative Damage and Improves the Growth Performance of Barley under Drought Stress

Drought is a severe environmental constraint,causing a significant reduction in crop productivity across the world.Salicylic acid(SA)is an important plant growth regulator that helps plants cope with the adverse effects induced by various abiotic stresses.The current study investigated the potential effects of SA on drought tolerance efficacy in two barley(Hordeum vulgare)genotypes,namely BARI barley 5 and BARI barley 7.Ten-day-old barley seedlings were exposed to drought stress by maintaining 7.5%soil moisture content in the absence or presence of 0.5,1.0 and 1.5 mM SA.Drought exposure led to severe damage to both genotypes,as indicated by phenotypic aberrations and reduction of dry biomass.On the other hand,the application of SA to drought-stressed plants protected both barley genotypes from the adverse effects of drought,which was reflected in the improvement of phenotypes and biomass production.SA supplementation improved relative water content and proline levels in drought-stressed barley genotypes,indicating the osmotic adjustment functions of SA under water-deficit conditions.Drought stress induced the accumulation of reactive oxygen species(ROS),such as hydrogen peroxide(H2O2)and superoxide(O_(2)•^(−)),and the lipid peroxidation product malondialdehyde(MDA)in the leaves of barley plants.Exogenous supply of SA reduced oxidative damage by restricting the accumulation of ROS through the stimulation of the activities of key antioxidant enzymes,including superoxide dismutase(SOD),peroxidase(POD),catalase(CAT),ascorbate peroxidase(APX)and glutathione peroxidase(GPX).Among the three-applied concentrations of SA,0.5 mM SA exhibited better mitigating effects against drought stress considering the phenotypic performance and biochemical data.Furthermore,BARI barley 5 showed better performance under drought stress than BARI barley 7 in the presence of SA application.Collectively,our results suggest that SA played a crucial role in improving water status and antioxidant defense strategy to protect barley plants from the deleterious effects of water deficiency.

Foliar Application of Benzothiadiazole and Salicylic Acid to Combat Sheath Blight Disease of Rice

A field study was undertaken to ascertain the effects of elicitors viz. benzothiadiazole （BTH） and salicylic acid （SA） on defense related enzymes viz. peroxidase, phenylalanine ammonia lyase, superoxide dismutase, chitinase and 13-1,3-glucanase, and phenols in rice （Pusa Basmati I） plants. First foliar spray of BTH （50 mg/kg） and SA （50 mg/kg） was done at the maximum tillering stage and inoculation with Rhizoctonia solani was carried 24 h after elicitor treatment. Elicitors were further sprayed at every growth stage. Time course analysis showed peak accumulation of defense related enzymes and phenols in the rice leaves treated with BTH and SA, and accumulation was the highest at the flowering stage. Higher enzymatic activity was observed in elicitor treated plants inoculated with R. solani. Compared to the untreated control plants, application of elicitors before R. solani inoculation significantly elicited the defense related enzymes and phenols. Moreover, application of elicitors had a positive effect on yield and disease reduction. It is suggested that pretreatment of rice leaves with BTH and SA could be used to enhance the level of protection against sheath blight and to improve rice yield in the fields.

Common mycorrhizal networks activate salicylic acid defense responses of trifoliate orange(Poncirus trifoliata)

Citrus canker, caused by Xanthomonas axonopo-dis pv. citri ('Xac'), is an important quarantine disease in citrus crops. Arbuscular mycorrhizal fungi (AMF) form symbiotic interactions with host plants and further affect their disease resistance, possibly by modulating the activity of salicylic acid (SA), a key phytohormone in disease resistance. Common mycorrhizal networks (CMNs) can interconnect plants, but it is not yet clear whether CMNs promote resistance to citrus canker and, if so, whether SA signaling is involved in this process. To test this possibility, we used a two-chambered rootbox to establish CMNs between trifoliate orange (Poncirus trifoliata) seedlings in chambers inoculated (treated) or not (neighboring) with the AMF, Paraglomus occultum. A subset of the AMF-inoculated seedlings were also inoculated with Xac (+AMF+Xac). At 2 d post-inoculation (dpi), compared with the +AMF-Xac treatment, neighboring seedlings in +AMF+Xac treatment had lower expression levels of the SA biosynthetic genes, PtPAL, PtEPS1, and PtPBS3, but higher SA levels, which attributed to the upregulation of PtPAL and PtPBS3 in treated seedlings and the transfer of SA, via CMNs, to the neighboring seedlings. At 4 dpi, the pathogenesis-related (PR) protein genes, PtPR1, PtPR4, and PtPR5, and the transcriptional regulatory factor gene, PtNPR1, were activated in neighboring seedlings of+AMF+Xac treatment. At 9 dpi, root phenylalanine ammo-nia-lyase activity and total soluble phenol and lignin concentrations increased in neighboring seedlings of+AMF+Xac treatment, likely due to the linkage and signal transfer, via CMNs. These findings support the hypothesis that CMNs transfer the SA signal from infected to neighboring healthy seedlings, to activate defense responses and affording protection to neighboring plants against citrus canker infection.

Salicylic Acid and its Function in Plant Immunity

The small phenolic compound salicylic acid （SA） plays an important regulatory role in multiple physiological processes including plant im- mune response. Significant progress has been made during the past two decades in understanding the SA-mediated defense signaling network. Characterization of a number of genes functioning in SA biosynthesis, conjugation, accumulation, signaling, and crosstalk with other hormones such as jasmonic acid, ethylene, abscisic acid, auxin, gibberellic acid, cytokinin, brassinosteroid, and peptide hormones has sketched the finely tuned immune response network. Full understanding of the mech- anism of plant immunity will need to take advantage of fast developing genomics tools and bioinformatics techniques. However, elucidating genetic components involved in these pathways by conventional ge- netics, biochemistry, and molecular biology approaches will continue to be a major task of the community. High-throughput method for SA quantification holds the potential for isolating additional mutants related to SA-mediated defense signaling.

Exogenous SA Initiated Defense Response and Multi-signaling Pathway in Tetraploid Potato SD20

Salicylic acid(SA) is an important signaling substance that plays an important role in plant growth, development and disease resistance.In order to further understand the role of the SA pathway in potato disease resistance and identify SA signaling key genes, gene expression profiling of the late blight resistance genotype SD20 was performed under exogenous SA application. A total of 28 572 unigenes were assembled,of which 4 564 were differentially expressed. Analysis of differentially expressed genes(DEGs) showed that multiple signaling pathways such as SA, jasmonic acid, ethylene, abscisic acid, auxin, and brassinolide were involved in response to exogenous SA. Many plant defense signalrelated genes involved in protein serine/threonine kinase activity and plant-pathogen interaction, were significantly enriched. These were consistent with the interaction results of SD20 and Phytophthora infestans in our previous study, indicating that exogenous SA stimulated the resistance response and initiated a similar defense pathway compared to pathogen infection in SD20, which confirmed crosstalk of the SA signaling pathway with a pathogen-induced disease resistance signal pathway in plant. Moreover, transcriptome analysis revealed that ROS1 was positively regulated by SA in potato for the first time. SA-induced gene expression profiling provides insight into SA signaling and its mechanisms in disease defense systems.

Herbivore-induced rice resistance against rice blast mediated by salicylic acid

In agro-ecosystems,plants are important mediators of interactions between their associated herbivorous insects and microbes,and any change in plants induced by one species may lead to cascading effects on interactions with other species.Often,such effects are regulated by phytohormones such as jasmonic acid(JA)and salicylic acid(SA).Here,we investigated the tripartite interactions among rice plants,three insect herbivores(Chilo suppressalis,Cnaphalocrocis medinalis or Nilapai-vata lugens),and the causal agent of rice blast disease,the fungus Magnaporthe oryzae.We found that pre-infestation of rice by C.suppressalis or N.lugens but not by C.medinalis conferred resistance to M.oryzae.For C.suppressalis and N.lugens,insect infestation without fungal inoculation induced the accumulation of both JA and SA in rice leaves.In contrast,infestation by C.medinalis increased JA levels but reduced SA levels.The exogenous application of SA but not of JA conferred resistance against M.oryzae.These results suggest that preinfestation by C suppressalis or N.lugens conferred resistance against M.oryzae by increasing SA accumulation.These findings enhance our understanding of the interactions among rice plant,insects and pathogens,and provide valuable information for developing an ecologically sound strategy for controlling rice blast.

PBS3 and EPS1 Complete Salicylic Acid Biosynthesis from Isochorismate in Arabidopsis

Salicylic acid(SA)is an important phytohormone mediating both local and systemic defense responses in plants.Despite over half a century of research,how plants biosynthesize SA remains unresolved.In Arabidop-sis,a major part of SA is derived from isochorismate,a key intermediate produced by the isochorismate syn-thase,which is reminiscent of SA biosynthesis in bacteria.Whereas bacteria employ an isochorismate pyru-vate lyase(IPL)that catalyzes the turnover of isochorismate to pyruvate and SA,plants do not contain an IPL ortholog and generate SA from isochorismate through an unknown mechanism.Combining genetic and biochemical approaches,we delineated the SA biosynthetic pathway downstream of isochorismate in Ara-bidopsis.We found that PBS3,a GH3 acyl adenylase-family enzyme important for SA accumulation,catalyzes ATP-and Mg2+-dependent conjugation of L-glutamate primarily to the 8-carboxyl of isochorismate and yields the key SA biosynthetic intermediate,isochorismoyl-glutamate A.Moreover,we discovered that EPS1,a BAHD acyltransferase-family protein with a previously implicated role in SA accumulation upon pathogen attack,harbors a noncanonical active site and an unprecedented isochorismoyl-glutamate A pyruvoyl-glutamate lyase activity that produces SA from the isochorismoyl-glutamate A substrate.Together,PBS3 and EPS1 form a two-step metabolic pathway to produce SA from isochorismate in Arabidopsis,which is distinct from how SA is biosynthesized in bacteria.This study closes a major knowledge gap in plant SA meta-bolism and would help develop new strategies for engineering disease resistance in crop plants.

Jasmonate- and salicylate-induced defenses in wheat affect host preference and probing behavior but not performance of the grain aphid, Sitobion avenae

Jasmonate and salicylatemediated signaling pathways play significant roles in induced plant defenses, but there is no sufficient evidence for their roles in monocots against aphids. We exogenously applied methyl jasmonate （MeJA） and salicylic acid （SA） on wheat seedlings and examined biochemical responses in wheat and effects on the grain aphid, Sitobion avenae （Fab.）. Application of MeJA significantly increased levels of wheat＇s polyphenol oxidase, peroxidase and proteinase inhibitor 1, 2 and 6 days after treatment. In twochoice tests, adult aphids preferred control wheat leaves to MeJA or SA treated leaves. Electrical penetration graph （EPG） recordings of aphid probing behavior revealed that on MeJAtreated plants, the duration of aphid＇s first probe was significantly shorter and number of probes was significantly higher than those on control plants. Also total duration of probing on MeJAtreated plants was significantly shorter than on control plants. Total duration of salivation period on SAtreated plants was significantly longer, while mean phloem ingestion period was significantly shorter than on control plants. However, no significant difference in total duration of phloem sap ingestion period was observed among treatments. The EPG data suggest that MeJAdependent resistance factors might be due to feeding deterrents in mesophyll, whereas the SAmediated resistance may be phloembased. We did not observe any significant difference of MeJA and SA application on aphid development, daily fecundity, intrinsic growth rate and population growth. The results indicate that both MeJA and SAinduced defenses in wheat deterred S. avenae colonization processes and feeding behavior, but had no significant effects on its performance.

Repression of the Arabidopsis thaliana Jasmonic Acid/Ethylene-Induced Defense Pathway by TGA-Interacting Glutaredoxins Depends on Their C-Terminal ALWL Motif

Glutaredoxins are small heat-stable oxidoreductases that transfer electrons from glutathione （GSH） to oxi- dized cysteine residues, thereby contributing to protein integrity and regulation. In Arabidopsis thaliana, floral glutare- doxins ROXY1 and ROXY2 and pathogen-induced ROXY19/GRX480 interact with bZIP transcription factors of the TGACG （TGA） motif-binding family. ROXY1, ROXY2, and TGA factors PERIANTHIA, TGA9, and TGA10 play essential roles in floral development. In contrast, ectopically expressed ROXY19/GRX480 negatively regulates expression of jasmonic acid （JA）/ ethylene （ET）-induced defense genes through an unknown mechanism that requires clade II transcription factors TGA2, TGA5, and/or TGA6. Here, we report that at least 17 of the 21 land plant-specific glutaredoxins encoded in the Arabidopsis genome interact with TGA2 in a yeast-two-hybrid system. To investigate their capacity to interfere with the expression of JA/ET-induced genes, we developed a transient expression system. Activation of the ORA59 （OCTADECANOID-RESPONSIVE ARABIDOPSIS AP2/ERF-domain protein 59） promoter by transcription factor EIN3 （ETHYLENE INSENSITVE 3） was sup- pressed by co-expressed ROXY19/GRX480. Suppression depended on the L＊＊LL motif in the C-terminus of ROXY19/ GRX480. This putative protein interaction domain was recently described as being essential for the TGA/ROXY interaction. Ten of the 17 tested ROXY proteins suppressed ORA59 promoter activity, which correlated with the presence of the C-terminal ALWL motif, which is essential for ROXY1 function in flower development. ROXY19/GRX480-mediated repres- sion depended on the GSH binding site, suggesting that redox modification of either TGA factors or as yet unknown target proteins is important for the suppression of ORA59 promoter activity.

Jasmonic acid carboxyl methyltransferase regulates development and herbivory-induced defense response in rice

Jasmonic acid（JA） and related metabolites play a key role in plant defense and growth. JA carboxyl methyltransferase（JMT） may be involved in plant defense and development by methylating JA to methyl jasmonate（Me JA） and thus influencing the concentrations of JA and related metabolites. However, no JMT gene has been well characterized in monocotyledon defense and development at the molecular level. After we cloned a rice JMT gene,Os JMT1, whose encoding protein was localized in the cytosol, we found that the recombinant Os JMT1 protein catalyzed JA to Me JA. Os JMT1 is up-regulated in response to infestation with the brown planthopper（BPH; Nilaparvata lugens）. Plants in which Os JMT1 had been overexpressed（oeJMT plants） showed reduced height and yield. These oe-JMT plants also exhibited increased Me JA levels but reduced levels of herbivore-induced JA and jasmonoyl-isoleucine（JAIle）. The oe-JMT plants were more attractive to BPH female adults but showed increased resistance to BPH nymphs,probably owing to the different responses of BPH female adults and nymphs to the changes in levels of H_2O_2 and Me JA in oe-JMT plants. These results indicate that Os JMT1,by altering levels of JA and related metabolites, plays a role in regulating plant development and herbivore-induced defense responses in rice.

外源水杨酸对黄瓜幼苗灰霉病防御酶活性的影响

为研究水杨酸(SA)对感染灰霉病黄瓜幼苗防御酶活性的影响,采用叶面喷施外源水杨酸(SA),测定SA对感染灰霉病黄瓜幼苗叶片中多酚氧化酶(PPO)、苯丙氨酸解氨酶(PAL)、过氧化氢酶(CAT)、过氧化物酶(POD)和过氧化物歧化酶(SOD)5种防御酶活性的影响。结果表明:不同浓度SA对黄瓜幼苗抗灰霉病均有作用,能显著降低黄瓜幼苗的病情指数,其中以150 mg·L^(-1)的SA处理后的相对防效最高。叶面喷施150 mg·L^(-1)的SA后,随感染天数的增加PPO、PAL、CAT、POD、SOD 5种防御酶的活性均呈现出先上升后下降趋势,感染期间经SA处理后的5种防御酶的活性均高于未处理,其中PAL活性持续性较好。外源水杨酸能通过促进防御酶活性提高黄瓜幼苗抵抗灰霉病的伤害,浓度为150 mg·L^(-1)的SA处理抵抗作用最好。

水杨酸对烟草病毒病的防效与烟苗生理活性的影响

【目的】探明喷施水杨酸对烤烟普通花叶病的防效与烟苗生理活性的影响,为水杨酸绿色防控烟草病毒病提供理论依据。【方法】采用漂浮育苗和盆栽试验方法研究喷施不同浓度[T_(1)(0.50 mmol/L)、T_(2)(0.75 mmol/L)和T_(3)(1.0 mmol/L)]水杨酸对烟株病毒病的病情指数和叶片防御酶活性的影响。【结果】喷施不同浓度水杨酸,烟苗叶片的防御酶活性在处理3~6 d时达最高峰;T_(1)和T_(2)防御酶活性和脯氨酸含量较高。其中,POD活性,T_(1)~T_(3)在处理3~6d时较清水对照(CK)分别提高68.00%~74.36%、34.23%~44.22%和4.39%~21.81%。SOD活性,在处理3 d时达最高,较CK分别提高49.47%、65.71%和27.27%。几丁质酶活性,T_(2)在处理3 d时达最高,为925.55 U/g;T_(1)和T_(3)在处理6 d时达最高,分别为1231.75U/g和820.45 U/g,T_(1)较CK提高67.12%。β-1,3-葡聚糖酶活性,均在处理3 d时达最高,较CK分别提高97.12%、59.37%和58.23%。脯氨酸含量,均在处理6 d时达最高,较CK分别提高29.41%、27.71%和17.80%。0.75mmol/L水杨酸处理烟株病毒病的病情指数为26.22,远低于CK(64.80),防控效果达59.53%。【结论】水杨酸可诱导烟叶POD、SOD、几丁质酶、β-1,3-葡聚糖酶活性和脯氨酸含量增加,与烟苗对病毒病的抗性密切相关。

Mechanisms of Optimal Defense Patterns in Nicotiana attenuata: Flowering Attenuates Herbivory-elicited Ethylene and Jasmonate Signaling

To defend themselves against herbivore attack, plants produce secondary metabolites, which are variously inducible and constitutively deployed, presumably to optimize their fitness benefits in light of their fitness costs. Three phytohormones, jasmonates （JA） and their active forms, the JA-isoleucine （JA-Ile） and ethylene （ET）, are known to play central roles in the elicitation of induced defenses, but little is known about how this mediation changes over ontogeny. The Optimal Defense Theory （ODT） predicts changes in the costs and benefits of the different types of defenses and has been usefully extrapolated to their modes of deployment. Here we studied whether the herbivore-induced accumulation of JA, JA-Ile and ET changed over ontogeny in Nicotiana attenuata, a native tobacco in which inducible defenses are particularly well studied. Herbivore-elicited ET production changed dramatically during six developmental stages, from rosette through flowering, decreasing with the elongation of the first corollas during flower development. This decrease was largely recovered within a day after flower removal by decapitation. A similar pattern was found for the herbivore-induced accumulation of JA and JA-Ile. These results are consistent with ODT predictions and suggest that the last steps in floral development control the inducibility of at least three plant hormones, optimizing defense-growth tradeoffs.

Isolation and characterization of a new defense gene from soybean

A cDNA clone of a single-copy gene designated SbPRP was isolated and characterized from 2-week-old soybean seedlings. It putatively encodes a bimodular protein similar to develop-mentally regulated proteins in other plant species. The deduced amino acid sequence consists of 126 amino acids with a distinct proline-rich domain (17 amino acids) and a long hydrophobically cysteine-rich domain (84 amino acids), plus a signal peptide of 25 amino acids in N terminal. SbPRP mRNA transcripts accumulated in an organ specific manner. It can be detected in leaves and epicotyls of soybean seedlings, whereas virtually expression signal of SbPRP was not detected in cotyledons, hypocotyls and roots. Further Northern hybridization suggested that SbPRP steady-state mRNA level accumulated differentially not only in response to salicylic acid, but to the inoculation of soybean mosaic virus Sa strain. Also it was responsive to drought treatment and salt (NaCI) stress. Therefore it is likely that SbPRP functions as a defense gene in soybean.

钙离子和茉莉酸灌根对菜豆叶片防御酶活性和西花蓟马取食偏好性的影响

为探明外源物质对菜豆植株防御酶活性和西花蓟马取食偏好性的影响。本试验分别采用CaCl_(2)和茉莉酸(JA)进行灌根,研究了西花蓟马取食前后菜豆叶片脂氧合酶(LOX)、丙二烯氧化物合酶(AOS)、超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)和多酚氧化酶(PPO)活性的变化,并研究了西花蓟马对JA和CaCl_(2)处理后的菜豆植株的取食偏好性。结果表明:不论CaCl_(2)还是JA灌根均可诱导菜豆防御酶AOS、LOX、CAT和SOD活性的上升,其中对CAT活性影响最大,其活性分别上升至对照的2.83倍和3.57倍,但对POD和PPO活性没有影响。西花蓟马取食CaCl_(2)处理的菜豆植株,能诱导LOX、POD和PPO活性分别上升1.40、2.03倍和2.26倍,而SOD活性则被显著抑制。西花蓟马取食JA灌根的菜豆植株能明显诱导POD和PPO活性的升高,二者活性分别是未取食植株的1.67倍和1.45倍,但AOS、LOX、CAT和SOD活性被抑制。西花蓟马2龄若虫取食CaCl_(2)和JA处理的菜豆植株,造成的损伤面积只有对照的53%和28%,取食选择率分别降低71%和66%。上述结果表明,CaCl_(2)和JA灌根能诱导菜豆植株的防御反应,减少蓟马的为害;西花蓟马取食能影响JA和CaCl_(2)灌根的菜豆植株防御酶活性的变化。

抗氧化系统参与水杨酸诱导烟草幼苗抗冷性提高的生化机制

烟草苗期冷害是影响烟草农业生产的一个重要问题,通过各种农艺措施来提高烟苗抗冷性有重要的实际意义。以2个烟草主栽品种‘云烟97’和‘K326’为材料,用浓度为0、0.5、1.0、1.5 mmol/L的水杨酸(SA)对其幼苗进行预处理后进行10℃的低温处理12 d。结果表明,与未处理的对照相比,SA预处理能显著降低‘云烟97’和‘K326’幼苗在低温胁迫过程中叶片的丙二醛(MDA)含量和电解质渗漏率,减缓干物质的消耗速度,增加叶绿素含量和增强根系活力,改善幼苗的根长、表面积、体积和根尖数,促进根系的生长,最终提高烟草幼苗的抗冷性。不同品种有不同的适宜的SA浓度,‘云烟97’的最适浓度为1.5 mmol/L,‘K326’的最适浓度为1.0 mmol/L;SA预处理后,与未预处理的对照相比,在进入低温处理前和低温处理期间,烟草幼苗抗氧化系统中的主要抗氧化剂还原型抗坏血酸(ASA)和谷胱甘肽(GSH)含量均保持在较高的水平,而氧化型ASA和GSH含量则保持在较低水平,还原型抗氧化剂在总抗氧化剂中的比例提高;主要的抗氧化酶抗坏血酸过氧化物酶(APX)、过氧化氢酶(CAT)、愈创木酚过氧化物酶(GPX)、谷胱甘肽还原酶(GR)和超氧化物歧化酶(SOD)均保持较高的活性。这些结果表明,SA预处理后,与未处理对照相比,烟草幼苗均能保持较高的还原型抗氧化剂水平和抗氧化酶活力,并且在低温胁迫期间依然能维持较高的抗氧化能力,这是SA处理能诱导烟草幼苗抗冷性提高的重要生化基础。研究结果不仅对烟草抗冷育苗有参考意义,也对其他农作物、蔬菜的育苗和早期栽培有借鉴作用。

Promotion of Arabidopsis immune responses by a rhizosphere fungus via supply of pipecolic acid to plants and selective augment of phytoalexins

The ascomycete insect pathogenic fungi such as Metarhizium species have been demonstrated with the abilities to form the rhizosphere or endophytic relationships with different plants for nutrient exchanges.In this study,after the evident infeasibility of bacterial disease development in the boxed sterile soils,we established a hydroponic system for the gnotobiotic growth of Arabidopsis thaliana with the wild-type and transgenic strain of Metarhizium robertsii.The transgenic fungus could produce a high amount of pipecolic acid(PIP),a pivotal plant-immune-stimulating metabolite.Fungal inoculation experiments showed that M.robertsii could form a non-selective rhizosphere relationship with Arabidopsis.Similar to the PIP uptake by plants after exogenous application,PIP level increased in Col-0 and could be detected in the PIP-non-producing Arabidopsis mutant(ald1)after fungal inoculations,indicating that plants can absorb the PIP produced by fungi.The transgenic fungal strain had a better efficacy than the wild type to defend plants against the bacterial pathogen and aphid attacks.Contrary to ald1,fmo1 plants could not be boosted to resist bacterial infection after treatments.After fungal inoculations,the phytoalexins camalexin and aliphatic glucosinolate were selectively increased in Arabidopsis via both PIP-dependent and-independent ways.This study unveils the potential mechanism of the fungus-mediated beneficial promotion of plant immunity against biological stresses.The data also highlight the added values of M.robertsii to plants beyond the direct suppression of insect pest populations.