Type Of Elicitor Research Articles

The Interaction of Humidity and Resistance Elicitors on Expression of Polygenic Resistance of Barley to Mildew

AbstractElicitor‐active glucan was applied to leaves of genotypes of barley expressing different levels of resistance to powdery mildew (Erysiphe graminis f. sp. hordei)which was assessed by measuring mildew colonies per leaf or speed of papilla induction response to mildew challenge. The influence of humidity was also assessed by treating leaves with glucan, inoculating with mildew and immediately sealing the leaves in Perspex containers in an apparatus which enabled temperature, air speed and humidity to be controlled accurately. In water‐treated controls low humidity alone reduced colonies per leaf, and at 60% r.h. genotype 7204 showed significantly less effect of humidity compared with other genotypes, although at 40% it responded as other genotypes. At low humidity glucan stimulated resistance for genotypes Proctor and 7204 but not for Golden Promise or 9855; the effect of humidity or elicitor alone was only significant on genotype 7204, Chitin also proved an effective elicitor, but at high and not at low humidity. Time of pre‐treatment before mildew challenge, leaf stage, type of elicitor, concentration of elicitor, post‐inoculation light regime, mildew isolate and barley genotype all had major influences on papilla response. Other factors were less important. Based on papilla formation, the barley cultivar Proctor was most and Golden Promise the least responsive to glucan as an elicitor. The potential for exploiting the genetic basis of inducible resistance is discussed.

Changes in the composition of exocellular proteins of suspension-culturedLupinus albuscells in response to fungal elicitors or CuCl2

Among many aspects of plant defence responses to pathogenic infection are changes in the composition of the exocellular matrix. To study potential defences in white lupin (Lupinus albus L.), suspension-cultured cells were treated for 24 h with one of three different elicitors : CuCl 2 , and two fungal elicitor preparations from purified cell walls of yeast and Colletotrichum lindemuthianum. Two subsets of exocellular proteins: ionicallybound wall proteins and proteins secreted into culture medium, were isolated, and their patterns compared following electrophoretic separation. Only a few proteins were observed in culture filtrates with dominating bands at 27, 33, and 42 kDa. About 30 proteins were observed in cell wall extracts. Changes in protein intensities evoked by elicitor treatments depended on the type of elicitor used, the age and composition of lupin cell culture, and concentration of applied fungal elicitor. Based on these observations, ten proteins were chosen for N-terminal sequencing, and sequences 5-30 amino acids long for nine proteins were obtained. Three of the major proteins sequenced were identified as acidic exocellular chitinase, polygalacturonase-inhibiting protein, and germin/oxalate oxidase.

Specificity in the immobilisation of cell wall proteins in response to different elicitor molecules in suspension-cultured cells of French bean (Phaseolus vulgaris L.)

A characteristic of the defence response is the immobilisation of wall proteins possibly through the formation of covalent cross-links and the subsequent barrier formation against pathogens. A requirement for this is the generation of active oxygen species, particularly hydrogen peroxide. In the present work, we examine in depth the requirement for H2O2 and the specificity of the immobilisation with respect to particular wall proteins. Salt-extractable wall proteins were analysed for hydroxyproline content and the subset of proteins with this post-translational modification was found to be small. About 50 proteins were found to be easily salt-extractable and in response to elicitor treatment about 5 were found to be specifically immobilised. Immobilisation was very rapid and completed within 15 min after elicitation, and dependent upon the type of elicitor and the intensity of the production of active oxygen species. N-terminal sequencing and amino acid analysis revealed that, apart from one polypeptide, all immobilised proteins were (hydroxy)proline-containing glycoproteins with O-linked oligosaccharide side chains. In contrast, N-linked glycoproteins were not immobilised. N-terminal protein sequencing revealed the immobilised HRGPs to be novel, but both extensin and PRP-like. Implications of these findings for both pathogenic and symbiotic processes are also discussed.

Abiotic elicitation of coumarin phytoalexins in sunflower

Detached leaves, leaf disks and cut stems and hypocotyls, but not roots of sunflower ( Helianthus annuus) plants accumulated the coumarin phytoalexins, scopoletin and ayapin, when treated with solutions of CuCl 2 or sucrose. Irradiation with shortware UV and exposure to Triton X-100 was also effective, while no effect was observed with longwave UV, salicylic acid, dichloroisonicotinic acid or glutathione. The elicitation of the coumarins was dependent on the type of elicitor used and the age of the plant tissues. Treatment with sucrose elicited similar amounts of scopoletin and ayapin while treatment with CuCl 2 favoured the formation of ayapin with low concentrations of scopoletin and none of the scopoletin 7- O-glucoside being observed. The selective induction of ayapin by CuCl 2 was associated with an inhibition in the activity of the O-glucosyltransferase responsible for glycosylating scopoletin, and an induction in a peroxidase which metabolized scopoletin but not ayapin. The abiotic elicitation of the phytoalexins increased in the leaves of sunflower as a function of age, with seedlings and immature plants being unable to synthesize scopoletin or ayapin. Inhibitor and precursor feeding studies were unable to elucidate the biosynthetic route to scopoletin although an elicitor-inducible methyltransferase activity which could methylate esculetin to produce scopoletin was identified.

Enhancement of anthocyanin production in callus cultures ofDaucus canota L. under the influence of fungal elicitors

Aqueous extracts of fungal biomass ofAspergillus niger, A. flavus, Penicillium notatum, Fusarium oxysporum and the filtrates of their culture media were analysed for elicitation capability to enhance anthocyanin production in callus cultures ofDaucus carota. The mycelial extract ofA. flavus at the 2.5% level gave maximum elicitation, which resulted in a two-fold increase in anthocyanin with maximal productivity of 23.7% on a dry weight basis. Whereas the media filtrates ofA. flavus induced a 1.25-fold increase in anthocyanin production with a yield of 20.6% on a dry weight basis,P. notatum andF. oxysporum were not as effective asA. flavus orA. niger. The contact time and the concentration required for maximal elicitation of anthocyanin differed with the type of elicitor used. Qualitative analysis of anthocyanins revealed the presence of cyanidin glycosides in control and elicited cultures.

Stress responses in alfalfa (Medicago sativa L.) IV. Expression of defense gene constructs in electroporated suspension cell protoplasts

We have investigated conditions for the uptake and expression of chimeric genes in protoplasts of alfalfa (Medicago sativa L.). Constructs containing the bacterial reporter gene chloramphenicol acetyltransferase (CAT) under the control of either the cauliflower mosaic virus 35S promoter or a bean chalcone synthase (CHS) promoter were introduced into protoplasts by electroporation in the presence of polyethyleneglycol. The extent of expression in the absence of added inducers depended on the conditions for isolation, electroporation and subsequent culture of the protoplasts. Expression of the CHS promoter construct was increased on exposure of the protoplasts to a fungal elicitor or reduced glutathione. The relative levels of induced expression in relation to either basal expression or the type of elicitor used depended on the age of the suspension cultures from which the protoplasts were isolated. Electroporation of protoplasts with a construct from which bean CHS antisense transcripts were synthesized under the control of the 35S promoter resulted in the inhibition of appearance of elicitor-induced endogenous alfalfa CHS activity. The suitability of the alfalfa protoplast system for analysis and potential identification of defense response genes is discussed.

A methyltransferase for synthesis of the phytoalexin 6-methoxymellein in carrot cells

Carrot ( Daucus carota L.) roots treated with 2-chloroethylphosphonic acid or uronide elicitor accumulated the phytoalexin 6-methoxymellein. The extracts of these cells catalyzed methylation of 6-hydroxymellein to 6-methoxymellein with S-adenosyl-L-methionine as a methyl donor. Activity of the O-methyltransferase was not found in fresh carrot roots but increased when they were treated with either type of elicitor in parallel with the increase in 6-methoxymellein content. The enzyme did not methylate 6-methoxymellein, 3,4-dehydro-6-methoxymellein, and some coumarin derivatives, though 3,4-dehydro-6-hydroxymellein accepted methyl moiety at the same rate as in 6-hydroxymellein.

Investigation of the mechanism of phytoalexin accumulation in soybean induced by glucan or mercuric chloride

Soybean cotyledons which had been treated with glucan from Phytophthora megasperma f.sp. glycinea or with mercuric chloride were pulse-labeled with 14CO 2 and then the 14C-incorporation into the phytoalexins was determined. The kinetics of 14C-incorporation into phytoalexins (glyceollin isomers and 3,6α,9-trihydroxypterocarpan) was very similar with the two types of elicitors. Metabolic rates of phytoalexins were determined by pulse-chase experiments. The apparent half-life of metabolism was about 100 h for glyceollin with either glucan or HgCl 2. The half-lives for trihydroxypterocarpan were 39 h with glucan and 14 h with HgCl 2. According to our results levels of glyceollins in soybean cotyledons are mainly controlled by their rates of synthesis. Biotic (glucan) and abiotic (HgCl 2) elicitors have similar induction effects. Both types of elicitors could act by effecting the release of endogenous elicitors.

Response sets in autistic echolalia.

Immediate echolalia, i.e., the tendency to repeat all or part of a conversational partner's utterance, is one of rhe most prevalent symptoms of verbal autistic children ( 1 ) . Echolalia appears to be multiply determined, relating to aspects of the conversational setting, to the child's comprehension of the propositional content of an eliciting utterance, and to the form of such an utterance ( 2 ) . Based on observations of a single child, Shapiro ( 3 ) has suggested an additional factor, namely, a tendency to adopt an echolalic response set which, once established, may result in echoing an elicitor that can be responded to appropriately in other circumstances. To evaluate Shapiro's hypothesis more systematically, we analyzed the verbal responses of five autistic, echolalic children (age M = 11.5 yr.) to two types of elicitors: Sentence Completion items (e.g., mommy is holding the .. ... .. .) and Wh questions (e.g., What is the mommy holding?). These utterance types were accompanied by appropriate pictures and were randomly interspersed with Yes/No question forms (e.g., Is the mommy holding the baby?). Based on data previously collected in a pretest (requiring a non-verbal, pointing response to an array of pictures), it appeared that the subjects had some comprehension of the basic propositions contained in these elicitors. Additional details regarding subjects' characteristics and procedures are given by Paccia-Cooper and Curcio ( 2 ) . The present analyses were restricted to Sentence Completion and Wh question items since these provoked a relatively low incidence of echolalia ( M = 5.2%) compared to Yes/No questions ( M = 59.4%) and so seemed best suited for evaluating Shapiro's hypothesis. The incidence of echolalia in response to these two forms was examined under two conditions: when a subject's response on the immediately preceding trial was echolalic vs when it was of a non-echolalic, complementary nature. If a response set exists, then echolalia should occur more frequently when the previous response was echolalic than for instances when the previous response was not echolalic. Analyses of 195 trials indicated that the mean percent of echolalic responses to Sentence Completion and Wh question items was higher when the preceding response aVas echolalic ( M = 11.7%) than when the preceding response was not echolalic ( M = 096, t = 2.15, p < 0.05). There was no instance of a subject echoing an eliciting utrerance when he had just given a non-echolalic response. These data support Shapiro's hypothesis of an echolalic response set among autistic children.