Detection of a wide spectrum of tobacco mosaic virus strains by indirect enzyme-linked immunosorbent assays (ELISA)

An automatic fluorescence phenotyping platform to evaluate dynamic infection process of Tobacco mosaic virus-green fluorescent protein in tobacco leaves

Tobacco is one of the important economic crops all over the world. Tobacco mosaic virus (TMV) seriously affects the yield and quality of tobacco leaves. The expression of TMV in tobacco leaves can be analyzed by detecting green fluorescence-related traits after inoculation with the infectious clone of TMV-GFP (Tobacco mosaic virus - green fluorescent protein). However, traditional methods for detecting TMV-GFP are time-consuming and laborious, and mostly require a lot of manual procedures. In this study, we develop a low-cost machine-vision-based phenotyping platform for the automatic evaluation of fluorescence-related traits in tobacco leaf based on digital camera and image processing. A dynamic monitoring experiment lasting 7 days was conducted to evaluate the efficiency of this platform using Nicotiana tabacum L. with a total of 14 samples, including the wild-type strain SR1 and 4 mutant lines generated by RNA interference technology. As a result, we found that green fluorescence area and brightness generally showed an increasing trend over time, and the trends were different among these SR1 and 4 mutant lines samples, where the maximum and minimum of green fluorescence area and brightness were mutant-4 and mutant-1 respectively. In conclusion, the platform can full-automatically extract fluorescence-related traits with the advantage of low-cost and high accuracy, which could be used in detecting dynamic changes of TMV-GFP in tobacco leaves.

Immunodetection of Furcraea Necrotic Streak Virus-FNSV in fique plants (Furcraea macrophylla Baker) using a polyclonal antibody IgY produced in chicken egg yolk

The necrotic streak of the fique (Furcraea spp.) or "Macana" disease is considered the most limiting disease for this crop in Colombia, whose causal agent is the Furcraea Necrotic Streak Virus - FNSV (RNA+). Currently, there are no strategies to control the disease, being necessary to develop methods for detection of this pathogen in the planting material before being taken to the field. In this study, polyclonal antibodies produced in egg yolk (IgY) were produced and assesses for detection FNSV. Two immunoenzymatic methodologies were standardized: Dot Blot Immunobinding Assay (DBIA) and Enzyme Linked Immunosorbent Assay (ELISA), determining their specificity and sensitivity. The detection limit by DBIA corresponded to 8 μg/mL of purified virus suspension using 10 μg/mL of primary antibody. In the ELISA test, the primary antibody concentration of 3 μg/mL (1:800 dilution) detected the antigen at concentrations between 10 and 70 μg/mL. The polyclonal antibody anti-FNSV IgY allowed the detection of FNSV in samples of purified virus and extracts of roots and leaves of fique plants with symptoms of "Macana" disease and did not produce any signal with the control samples. Results showed the potential of using egg yolk IgY in immunological tests for the detection of FNSV in fique plants.

A multiplex reverse transcription PCR assay for simultaneous detection of five tobacco viruses in tobacco plants

Tobacco viruses including Tobacco mosaic virus (TMV), Cucumber mosaic virus (CMV), Tobacco etch virus (TEV), Potato virus Y (PVY) and Tobacco vein banding mosaic virus (TVBMV) are major viruses infecting tobacco and can cause serious crop losses. A multiplex reverse transcription polymerase chain reaction assay was developed to detect simultaneously and differentiate all five viruses. The system used specific primer sets for each virus producing five distinct fragments 237, 273, 347, 456 and 547 bp, representing TMV, CMV subgroup I, TEV, PVY(O) and TVBMV, respectively. These primers were used for detection of the different viruses by single PCR and multiplex PCR and the results were confirmed by DNA sequencing analysis. The protocol was used to detect viruses from different parts of China. The simultaneous and sensitive detection of different viruses using the multiplex PCR is more efficient and economical than other conventional methods for tobacco virus detection. This multiplex PCR provides a rapid and reliable method for the detection and identification of major tobacco viruses, and will be useful for epidemiological studies.

Transmission of Activated-Episomal Banana streak OL (badna)virus (BSOLV) to cv. Williams Banana (Musa sp.) by Three Mealybug Species

Four different mealybug species (Dysmicoccus brevipes, Planococcus citri, P. ficus, and Pseudococcus longispinus) were evaluated for their ability to transmit putative activated-episomal Banana streak OL (badna)virus (BSOLV) to banana cv. Williams (Cavendish subgroup, AAA). Expressible endogenous sequences of banana streak viruses (BSVs) have been reported to be present in the DNA of various Musa hybrids, including FHIA-21 (AAAB). To obtain activated episomal BSOLV for this experimental transmission study, intentional stress by tissue culture propagation was applied to indexed FHIA-21 which, while free of other viruses, can contain activated episomal BSOLV. Immunocapture polymerase chain reaction and triple-antibody sandwich enzyme-linked immunosorbent assay results revealed that 13.4% of the derived progeny of the mother plants were infected with episomal BSOLV. Four of these BSOLV-infected progeny were used as sources of episomal virus for transmission studies. D. brevipes, Planococcus citri, and P. ficus mealybugs were able to transmit the putative activated episomal BSOLV. Control plants for the transmission experiments included FHIA-21 corms with no background history of tissue culture, as well as virus-free Williams plants. Episomal Banana streak GF (badna)virus (BSGFV) was transmitted from asymptomatic corm-derived FHIA-21 plants by P. citri and P. ficus. This is the first report of P. ficus as a vector of BSVs.

Identidade e propriedades de isolados de potyvírus provenientes de Capsicum spp

Vinte isolados virais provenientes de Capsicum spp. foram coletados em Minas Gerais, São Paulo, Espírito Santo e Rio de Janeiro visando definir a etiologia dos mosaicos. Para a caracterização biológica realizou-se teste de gama de hospedeiros e inoculação em cultivares diferenciadoras de pimentão (Capsicum annuum). Dois isolados provenientes de batata (Solanum tuberosum) (PVY N-BR e PVY O-BR) foram utilizados como controles. Os resultados indicaram considerável grau de variabilidade biológica entre os isolados, embora todos tenham sido identificados preliminarmente como Potato virus Y (PVY). A reação das cultivares diferenciadoras classificou os isolados como patótipo 1 ou 1.2 de PVY. Anti-soros foram produzidos a partir de partículas virais purificadas de um isolado fraco e um forte. O uso desses anti-soros em ELISA indireto levou a resultados positivos contra os isolados testados. Os anti-soros reagiram também contra PVY N-BR e PVY O-BR, embora este último tenha apresentado reação mais fraca. Para caracterização molecular, seqüenciaram-se os genes da polimerase (NIb) e da proteína capsidial (cp), e da região 3' não-traduzida (3'NTR) de isolados biologicamente distintos. A análise filogenética confirmou a identidade de seis isolados como Pepper yellow mosaic virus (PepYMV), um potyvírus descrito recentemente infetando pimentão no Brasil. Esse resultado sugere que o PepYMV pode ser a espécie de potyvírus predominante em Capsicum spp. no Brasil. O fato de isolados de PepYMV apresentarem gama de hospedeiros semelhante à do PVY, e de os dois vírus apresentarem relacionamento sorológico, ressalta a utilidade da análise molecular para a classificação de potyvírus provenientes de Capsicum spp.

Comparison of Detection Methods for a Novel Tobamovirus Isolated from Florida Hibiscus

A novel tobamovirus recently was isolated from hibiscus in Florida. Serological and molecular methods, including enzyme-linked immunosorbent assay (ELISA), dot-blot immunoassay (DBIA), tissue-blot immunoassay (TBIA), and immunocapture reverse-transcription poly-merase chain reaction (IC-RT-PCR) were compared to evaluate their usefulness for diagnosis of this virus. Each method was tested with partially purified virus preparations and tissue samples from infected hibiscus and Chenopodium quinoa plants. Indirect ELISA was more sensitive than double-antibody sandwich (DAS)-ELISA with all samples tested. The Florida hibiscus virus was detectable in hibiscus leaves and bark up to 1:12,800 and 1:6,400 dilutions, respectively, by indirect ELISA and up to 1:3,200 and 1:400 dilutions by DAS-ELISA. End-point dilutions of partially purified virus preparations from indirect and DAS-ELISA were 4 and 31 ng/ml, respectively. Florida hibiscus virus was detected by DBIA in sap from hibiscus bark and leaves at dilutions up to 1:400 and 1:800, respectively, showing that DBIA was less sensitive than either ELISA method. The virus also was detected reliably by TBIA from leaves and bark of hibiscus plants. The most sensitive method was IC-RT-PCR, which could detect as little as 500 pg/ml of virus in partially purified preparations and was 16- and 32-fold more sensitive than DAS-ELISA with hibiscus bark and leaf extracts, respectively. Over 600 hibiscus samples were tested by various combinations of these methods to validate their usefulness.

Interaction between viruses and monoclonal antibodies studied by surface plasmon resonance

An automated biosensor system designed for measuring molecular interactions in real time and without any labelling of the reactants has been used to study the interaction of two animal viruses (vaccinia virus and poliovirus) and two plant viruses (cowpea mosaic virus and tobacco mosaic virus) with monoclonal antibodies. Using monoclonal antibodies specific for different conformational states of viral protein, it was found that the virus particles retained their conformational integrity when immobilized on the dextran matrix present on the sensor chip. Compared to conventional solid phase immunoassays, in which immobilized proteins are usually partly denatured, the biosensor system presents several advantages for studying virus-antibody interaction.

Production of avian antibodies to three potyviruses in coturnix quail

Avian antibodies against three potyviruses were produced in a small bird, coturnix quail (Coturnix coturnix japonica Temminck et Schlegel), with 15-60 micrograms of purified virus preparations. Intramuscular injections of immunogen with Freund's incomplete or complete adjuvant into the birds did not result in higher titer of antibody compared to that of control birds given intravenous injections. Quail egg yolk antibody was as useful as hen antibody for indirect-ELISA and allowed virus to be detected in purified preparation (10-50 ng/ml) and in crude extracts (10(-6)-10(-7) dilution). The advantages of using quail to produce avian antibodies are discussed.

The use of peroxidase anti-peroxidase (PAP) complexes in the detection of plant viruses by ELISA

An ELISA test system for detection of plant viruses in field samples is described, based on the unlabelled antibody method using a peroxidase-antiperoxidase (PAP) complex. Novel features of the system include the use of acid-treated naked bacteria as combined carrier-adjuvants for the production of rabbit antiviral antibodies, and the use of acid-treated chicken antibodies (IgY) for antigen trapping in the ELISA. Systems for detection of potato virus Y (PVY), potato leafroll virus (PLRV), grapevine fanleaf virus (GFV) and grapevine virus A (GVA) were developed and compared with conventional direct double antibody sandwich (DAS) systems in tests with both purified virus and field samples. The PAP systems offer improved sensitivity, no background problems in the outer rows of the microtitre plates and are much easier to visualize with the naked eye if no plate reader is available.

Quantitation of serological cross-reactivity between two geographical isolates of Oryctes baculovirus by a modified ELISA

An assay was developed for quantitation of the antigenic relationship between viruses, by modification of the indirect ELISA. The principle of this method is to estimate the epitopes not shared between the related viruses, after titration of the antibodies specific to the common epitopes as in a blocking ELISA. In practice, varying concentrations of purified virus are preincubated with a fixed dilution of heterologous or homologous antiserum and the unbound antibodies present in the mixture are back titrated with virus particles bound to microtitre plates. The antigenic relationship is described in terms of differentiation index (DI) and total antigenic reactivity (TAR). This method has been used to quantitate cross-reactivity between two geographically different isolates of Oryctes baculovirus.

Use of rabbit Fab'-peroxidase conjugates prepared by the maleimide method for detecting plant viruses by ELISA

In contrast to antibodies conjugated to enzyme with glutaraldehyde or by the periodate method, monomeric Fab' fragments conjugated to enzyme by means of a maleimide compound are not adversely affected by the conjugation procedure. We used such Fab'-enzyme conjugates prepared with antibody to tobacco mosaic virus (TMV), to TMV coat protein and to rabbit IgG for the detection of different tobamoviruses by direct and indirect double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA). Compared to conjugates prepared by other methods, the sensitivity of TMV detection with Fab'-enzyme conjugates by direct DAS-ELISA was markedly increased. However, because of their monomeric nature, these FAb'-enzyme conjugates did not cross-react with serologically related tobamoviruses. Anti-globulin Fab'-enzyme conjugate was found to be the most efficient anti-globulin conjugate for detecting TMV by indirect DAS-ELISA. Because of their high sensitivity and serotype specificity, FAb'-enzyme conjugates are useful for detecting low amounts of contaminating viruses present in crude viral preparations.

Spurious cross-reactions between plant viruses and monoclonal antibodies can be overcome by saturating ELISA plates with milk proteins

It has been claimed recently [Dietzgen (1986) Arch Virol 91: 163-173] that a series of monoclonal antibodies (Mabs) produced against the nepovirus, arabis mosaic virus (ArMV) cross-reacted with the tobamovirus, tobacco mosaic virus (TMV). In the present report, this alleged cross-reactivity was re-examined by two ELISA procedures using Mabs produced against each of the two viruses. It was found that when highly concentrated preparations of Mabs were used, all antibodies reacted in a nonspecific manner with several plant viruses. However, when defatted milk instead of bovine serum albumin was used both as blocking agent and as diluent for the Mabs, the spurious cross-reactions between unrelated viruses were abolished. The use of milk as blocking agent did not prevent the detection of genuine cross-reactions between related nepoviruses.

Specific and sensitive detection of purified HLA molecules in an ELISA using mouse, rabbit and human anti-HLA antibodies

An ELISA detecting anti-HLA antibodies of rabbit, mouse or human origin was developed using plates coated with HLA molecules purified on affinity columns. The sensitivity of the assay was optimal when coating was performed in PBS, pH 7.8 at 4 degrees C for 6-16 h and using a serum incubation period of 16 h at 4 degrees C. The optimum protein concentration for coating was estimated to be 1 micrograms/ml. With monoclonal anti-HLA sera, antipeptide antibodies from mice or rabbit and human alloantisera, this method appeared to be highly sensitive, very specific and reproducible.

Visualization by electron microscopy of the location of tobacco mosaic virus epitopes reacting with monoclonal antibodies in enzyme immunoassay

The binding of monoclonal antibodies obtained after immunization with tobacco mosaic protein was analyzed by electron microscopy. A method was developed for visualizing the viral antigen reacting in different ELISA procedures. It was found that the use of a pH 9.6 buffer during the coating of ELISA plates led to the dissociation of virions into subunits which bound preferentially to the solid phase. MAbs that reacted with both virions and subunits in ELISA were found to bind to one of the two extremities of viral rods. These MAbs also reacted with viral protein aggregated in the form of disks. In contrast, MAbs reacting only with virions in ELISA were found to bind over the entire surface of the virus.

Accessibility of three continuous epitopes in tomato bushy stunt virus

Three peptides corresponding to residues 28-40, 138-154 and 380-387 of the coat protein of tomato bushy stunt virus (TBSV) were synthesized by the solid phase method and used to raise specific antibodies. These antibodies were used to follow the conformational changes that occur when TBSV particles swell under slightly alkaline conditions. Peptides 28-40 and 380-387 were found to correspond to continuous epitopes in the dissociated viral protein as well as in both compact and swollen virions. The region 138-154, which is also a continuous epitope of the monomeric protein, became accessible to antibody binding in the virion only when the particles were in the swollen state.

Conformational specificity of monoclonal antibodies used in the diagnosis of tomato mosaic virus

Ten monoclonal antibodies (McAbs) were raised to the tobamovirus, tomato mosaic virus (ToMV). Seven of the McAbs reacted with ToMV only when tested in an ELISA format, involving antibody-coated plates, which preserved the quaternary conformation of the viral protein. Two McAbs which reacted with ToMV only in an ELISA using virus-coated plates recognized an antigenic determinant present only on the disassembled form of the viral coat protein. One McAb reacted with both the assembled and dissociated forms of ToMV protein. All McAbs reacted in an identical manner with the 15 ToMV strains and isolates tested, confirming the previously established serological homogeneity of the ToMV species. Only two of the McAbs cross-reacted with two other tobamoviruses: tobacco mosaic virus (TMV) and ribgrass mosaic virus. Seven variations of ELISA were compared for their suitability to detect ToMV and TMV in tomato plants. Double antibody sandwich ELISA could be performed with a single McAb to ToMV as enough accessible epitopes are present on the virus to bind simultaneously to the coating and biotin-labelled antibody.

A method for the quantitative analysis of ELISA data

A method is described for measuring relationships among virus serotypes. An indirect ELISA was used to obtain antibody-response curves for homologous and heterologous combinations of virus and dilutions of antibody. Data from the proportional response region of each curve were converted to logarithmic values and subjected to a form of regression analysis to derive relative titres for the various combinations of virus and antibody. SDI values were then obtained by calculating the mean difference in relative titres between homologous and reciprocal heterologous combinations. Virus models in two different groups were examined using this technique. Relative titres obtained were consistent and reproducible over several experiments indicating that the technique was capable of reliably discriminating among serotypes which differed by as little as 0.2 SDI.

Detection and identification of plant viruses by ELISA using crude sap extracts and unfractionated antisera

A simple and rapid procedure of enzyme immunoassay (PTA-ELISA) was used to detect and identify viruses in individual plants. Virus antigen in crude leaf extracts was adsorbed directly to a solid-phase support, allowed to react with unfractionated antiserum and the antigen-antibody complex detected with a general purpose conjugate of protein A and enzyme. Viral antigens were trapped most effectively by high bonding polystyrene microtitre plates loaded with leaf extracts prepared in carbonate buffer at pH 9.6. With protein A-alkaline phosphatase conjugate and the substrate p-nitrophenyl phosphate as the antibody-detection system, 18 plant viruses in 8 virus groups were detected reliably and nonspecific reactions did not occur. However, when the substrate 3,3',5,-tetramethyl benzidine was used in conjunction with protein A-horseradish peroxidase conjugate, nonspecific reactions were given by leaf extracts from some uninfected or virus-infected plant species. Where less sensitivity is required than is provided by versions of ELISA that rely on antibody-captured antigen, this method provides a simple and rapid means of detecting and identifying viruses in crude sap extracts with the aid of unfractionated antisera.

Use of egg-yolk antibody for detection of respiratory syncytial virus in nasal secretions by ELISA

Egg-yolk immunoglobulins extracted from the eggs of hens immunized with respiratory syncytial virus (RSV) have been used as a reagent in double sandwich ELISA for detecting RSV in nasal secretions. The sensitivity of virus detection was the same in indirect ELISA, using rabbit anti chicken globulin conjugate, as when biotinylated yolk globulin and labeled avidin were used for detection. The specificity of ELISA for detecting RSV using yolk antibody was similar to that achieved by indirect immunofluorescence using commercial reagents of mammalian origin. Purified immunoglobulin was easily extracted from egg yolk; the amount of globulin present in a single preparation obtained from a batch of ten eggs was sufficient to carry out 10(6) ELISA tests for RSV detection.

Use of the biotin-avidin system for detecting a broad range of serologically related plant viruses by ELISA

The biotin-avidin detection system was used in direct and indirect ELISA for detecting a broad range of serologically related tobamoviruses. When compared to standard ELISA procedures that use antibodies labelled with alkaline phosphatase, the biotin-avidin system increased the assay sensitivity and allowed a wider range of related viral serotypes to be detected.

Use of chicken and rabbit antibodies in a solid phase protein A radioimmunossay for virus detection

A new rapid indirect solid phase radioimmunoassay was developed for the detection of Sindbis virus. Chicken antibodies were adsorbed onto wells in microplates to serve as 'capture antibodies' and rabbit antibodies were used as the second antibody. 125I-labelled protein A that does not bind to chicken antibodies, but binds firmly to rabbit antibodies was used as the tracer. All the steps necessary for the development of the assay are described. The minimal amount of Sindbis virus detectable was around 3 x 10(5) PFU/ml and the interassay reproducibility was about +/- 30%.

Plant virus detection using a new form of indirect ELISA

A novel form of indirect enzyme-linked immunosorbent assay (ELISA) has been devised for the detection of viruses in plants. The method uses protein A in two applications to sandwich antibody-antigen-antibody layers. The first applied layer of protein A prepares the plate for the coating antibody layer. The second layer of protein A is conjugated to the enzyme and detects the second antibody layer. The orientation of the IgG induced in the coating layer of antibody prevents later unwanted reaction with the conjugated protein A. Using seven antisera, protein A sandwich ELISA (PAS-ELISA) detected homologous virus isolates in standard dilutions of infected plant homogenates at A405 values which were at least one absorbance unit greater than those of healthy controls. The PAS-ELISA method was more sensitive than the direct double antibody sandwich form of ELISA (DAS-ELISA), e.g. not only were A405 values for homologous reactions greater in PAS-ELISA but also an antiserum to a birch isolate of cherry leaf roll virus detected four related isolates with the new method against only one with DAS-ELISA. However, dilution end points for the homologous virus were about the same in both methods. In a practical application, PAS-ELISA detected prune dwarf virus in 18-36% of tested Prunus avium seeds.

Quantitative microcomplement fixation tests using chicken anti-viral antibody extracted from egg yolk

Yolk immunoglobulins obtained from hens immunized with human rotavirus and two plant virus antigens were used in quantitative microcomplement fixation tests. Difficulties inherent in the use of avian complement were overcome by utilizing a mixture of the C1 component of chicken complement and guinea-pig complement devoid of its own C1. The method is suitable for detecting small quantities of viral antigen and antibody and for detecting antigenic activity present on peptide fragments of viral proteins.

Use of ELISA for measuring the extent of serological cross-reactivity between plant viruses

The degree of antigenic relatedness between two plant viruses is commonly expressed by a serological differentiation index (SDI) which corresponds to the average number of two-fold dilution steps separating homologous from heterologous precipitin titers. Results obtained with several tobamo- and tombusviruses indicated that the indirect form of the enzyme-linked immunosorbent assay (ELISA) can also be used for calculating SDI values. This was achieved by comparing the antiserum dilutions that lead to the same absorbance measurements (for instance 1.0) when homologous and heterologous viruses are assayed by ELISA. SDI values calculated from ELISA were similar to those obtained from precipitin tests. Because of its greater sensitivity, ELISA is able to quantify weak cross-reactions that are not detectable by precipitin tests.

Synthetic peptides as antigens: pitfalls of conjugation methods

Peptide-carrier conjugates were prepared using 9 different synthetic peptides, 3 carrier proteins and 4 coupling reagents. Residues of the carrier protein that were modified by different coupling reagents (e.g., glutaraldehyde, carbodiimides, bis-diazotized benzidine) were found to elicit specific antibodies that reacted with unrelated carrier proteins treated with the same coupling agent. To demonstrate the presence of peptide antibodies in an antiserum raised against a peptide-carrier conjugate, it was necessary to use a antigen the peptide coupled to another carrier by means of a different coupling agent. Some of the commonly used conjugation methods were found to lead to conjugates of insufficient stability and sometimes also altered the antigenic properties of the peptide moiety. These difficulties can be overcome by additional control experiments designed to test the quality and the peptide-carrier conjugates.

Detection of distant antigenic relationships between insect and bird lysozymes by ELISA

We used an indirect enzyme-linked immunosorbent assay (ELISA) for measuring the immunological cross-reactivities between bird lysozymes and a lysozyme isolated from the blood of the insect Locusta migratoria. The degrees of cross-reactivity among five avian lysozymes measured by ELISA agreed approximately with those observed in earlier work using microcomplement fixation tests. This latter technique is not suitable for detecting immunological cross-reactivity between proteins that differ in sequence by more than 30%-40%. In contrast, ELISA is able to detect distant relationships between antigens such as lysozymes that differ in sequence by as much as 60%. It seems likely that the use of ELISA procedures will extend the range of homologous proteins that can be compared by immunochemical means.

Determination of IgG and IgM levels in serum by rocket immunoelectrophoresis using yolk antibodies from immunized chickens

A method of rocket immunoelectrophoresis based on the use of avian antiglobulin antibodies is described which permits the quantitation of IgG and IgM in human serum. The electrophoretic mobility of avian yolk immunoglobulin (IgY) and mammalian IgG is sufficiently different to obviate the need to chemically modify the antibody, for example by carbamylation. Rockets are obtained in agarose within 3-6 h in 2-(N-morpholino) ethane sulfonic acid buffer at pH 5.5 or 6.0. Avian globulins specific for human IgG and IgM were obtained easily and in large quantities from the egg yolk of hyperimmunized laying hens. The technique is also applicable to quantitation of immunoglobulins in various animal sera.

Extension of the ELISA method to the measurement of the specific radioactivity of viruses in crude cellular extracts

The double-antibody sandwich method of ELISA, which allows accurate quantitative determination of plant viruses, was extended to a radiochemical procedure which permits direct measurement of the specific radioactivity of virus labelled in vivo and present in very crude plant homogenates. Evidence is presented showing that 20 to 50% of the virus introduced in the polystyrene wells during the antigen incubation step could be trapped in the sandwich. The percentage of virus bound increased with the concentration of the coating antibody and was almost proportional to the concentration of the antigen and to the incubation time of the antigens. Complete dissociation of the double-antibody sandwich was achieved by incubation with 0.2 M KOH or NaOH (pH 13.3), and the label carried by the virus was measured by scintillation counting of the solubilization fluid. The ratio infected/healthy was much higher for the radiochemical procedure than for the immunosorbent assay itself since binding of the virus to the coating antibody was not accompanied by any nonspecific trapping of radioactive contaminants in the double-antibody sandwich. The procedure was highly sensitive since the background corresponded to the scintillation counting background. The detection of label carried by tobacco mosaic virus was possible when the tobacco samples contained at least 5 ng of virus carrying a label as low as 40 dpm 3H or 20 dpm 14C.

Plant disease and the regulation of enzymes involved in lignification : Effects of osmotic pressure on phenylpropanoid enzymes and on the hypersensitive response of tobacco to tobacco mosaic virus

Tobacco varieties carrying the N gene from Nicotiana glutinosa respond to infection by Tobacco Mosaic Virus (TMV) by forming necrotic local lesions (hypersensitive reaction), thereby localizing the infection. In this study, infected mesophyll leaf tissue of N. tabacum Samsun NN was treated with the non-permeating, non-metabolizable carbohydrate mannitol. The local lesions developed under iso-osmotic conditions (0.28 M mannitol), though with a slight delay and with a reduced rate of growth, as compared to those on attached leaves. At increasing plasmolysing concentrations of mannitol, necrotization was progressively inhibited, but not completely suppressed. The leaf tissue produced tiny translucent zones, with a delay that increased between the virus inoculation and application of the plasmolytica. Activities of phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) and O-methyltransferase (OMT, EC 2.1.1.6) are strongly stimulated in hypersensitively reacting tobacco and were used as biochemical markers in the present study. This study was done to determine whether the inhibitory effect of plasmolysis on the elicitation of the hypersensitive response is due to a decrease in virus spread, resulting from the rupture of plasmodesmata or, at least in part, to metabolic alterations of the host cell exposed to osmotic stress. Since necrotization is normally preceded by intense virus multiplication, the inhibitory effects found for early applications (i.e., before local lesion appearance) of plasmolytica could easily be related to an inhibition of virus spread which also occurred in similarly treated leaf tissue of the systemically reacting variety Samsun. The most meaningful data were obtained from mannitol treatments performed on leaf tissue already carrying local lesions, i.e., in which the elicitor(s) and/or the factor(s) of necrotization were already operating. Under iso-osmotic conditions, we found the stimulated PAL and OMT activities characteristic of the hypersensitive response. At plasmolysing concentrations of mannitol, we observed the counteracting effects of two different mechanisms controlling the phenylpropanoid enzymes. Floating the leaf material on the liquid medium induced an ageing-like effect with a continuous increase in enzyme activities that was independent on osmotic pressure and sensitive to cycloheximide. At the same time, the stimulated enzyme activities related to hypersensitivity decreased at a rate related to osmotic pressure. Since PAL and OMT of tobacco leaves are long-lived enzymes, it is likely that the increased de novo synthesis of the enzymes was suppressed by plasmolysis while their degradation and/or inactivation was maintained or even increased. From these results it is concluded that the apparent inhibition of the hypersensitive response by plasmolysis is due to both a decrease in virus spead (artificially caused by the rupture of connections between cells) and to drastic metabolic alterations of the host cell exposed to high osmotic pressure.

Enzyme-assisted immune detection of plant virus proteins electroblotted onto nitrocellulose paper

A technique for the detection of plant virus coat proteins in plant sap is described. The method entails the electroblotting of sodium dodecyl sulphate-polyacrylamide gel electrophoresis-fractionated plant extracts onto nitrocellulose paper, probing the paper with virus-specific rabbit antisera, and indirect detection of virus proteins with horseradish peroxidase-conjugated goat anti-rabbit globulins. The sensitivity and specificity of the technique were tested using brome mosaic and barley stripe mosaic viruses. As little as 1 ng per track of virus protein was detectable, either as pure virus or when mixed with plant sap. Distant serological relationships were detected amongst tobamoviruses, and amongst the bromoviruses, with single antisera. The uses of the technique in probing capsid configuration in a presumed aphid picornavirus, and in routine diagnostic practice, are described.

Serological differentiation of tobamoviruses by means of monoclonal antibodies

Several serologically related plant viruses have been differentiated for the first time by means of monoclonal antibodies. Two orchid strains of tobacco mosaic virus that were previously considered to be serologically identical with the type strain were shown to be distinguishable with certain monoclonal antibodies. In indirect ELISA, none of the antibodies showed any binding to tobamoviruses that differed from TMV (common strain) by a serological differentiation index larger than 2. Monoclonal antibodies are likely to find widespread use as diagnostic tools in plant virology.

Comparison of direct and indirect ELISA for detecting antigenically related cucumoviruses

The suitability of two ELISA procedures for detecting serologically closely related as well as distantly related cucumoviruses has been compared. When antibodies to a single strain were used, closely related strains of cucumber mosaic virus could be detected by both direct and indirect ELISA. However, only the indirect ELISA procedure was capable of detecting distantly related viruses such as tomato aspermy, peanut stunt and cucumber mosaic viruses.

Biological and biochemical investigations on five European isolates of Mamestra brassica nuclear polyhedrosis virus

Five multiply enveloped European isolates of Mamestra brassicae nuclear polyhedrosis virus (Oxford, German, French, Dutch and Danish) were found to be very closely related serologically using the enzyme linked immunosorbent assay (ELISA) double antibody sandwich method and immunodiffusion. By SDS-polyacrylamide gel electrophoresis of viral proteins and restriction endonuclease analysis of DNA using seven enzymes there appeared to be two variants as the Oxford and German isolates were distinct from the other three. The German isolate was shown to be more susceptible to Nonidet P40 detergent treatment affecting some nucleocapsid structural polypeptides which also reduced antigenicity in gel immunodiffusion plates. In bioassays of polyhedra, the Dutch isolate showed a higher LD50 than the other viruses although this was not statistically significant.

Comparison of immunosorbent electron microscopy, enzyme immunoassay and counterimmunoelectrophoresis for detection of human rotavirus in stools

The detection of human rotaviruses by routine electron microscopy examination of stool specimens has been compared with the sensitivity of detection obtainable by three different immunoassays. These assays are: 1) immunosorbent electron microscopy (ISEM), which consists of the serological trapping of viruses on electron microscopy grids coated with protein A and specific viral antiserum; 2) an enzyme-linked immunosorbent assay (ELISA), in which the primary antibody is rabbit anti-rotavirus immunoglobulin, the secondary antibody is chicken anti-rotavirus immunoglobulin extracted from egg yolk of immunized hens, and the indicator antibody is alkaline phosphatase-conjugated rabbit anti-chicken immunoglobulin; 3) counterimmunoelectrophoresis (CIE). A total of 63 stool specimens from infants with gastroenteritis were examined. Of these, 23 and 24 specimens were found to contain rotavirus by electron microscopy and CIE, respectively. When scored by ELISA and ISEM, 37 and 39 were found to be positive, respectively. Confirmatory inhibition assays were necessary to eliminate some false positive reactions in ELISA. Detection of human rotaviruses in stools by ISEM is as sensitive as by ELISA, but in weakly positive specimens, ISEM offers the additional advantage of a direct visual demonstration of the presence of the aetiological agent.