An immunoelectron microscopic investigation of oat sterile dwarf and related viruses

PROPRIEDADES DE ISOLADOS VIRAIS DE SACCHARUM SPP. CAUSADORES DE MOSAICO EM CANA-DE-AÇÚCAR NO PARANÁ E SÃO PAULO

RESUMO Os vírus causadores do mosaico da cana-de-açúcar encontram-se disseminados em todas as regiões canavieiras do mundo, podendo infectar culturas de milho, sorgo e outras gramíneas. Este trabalho teve como objetivo determinar as propriedades de isolados paranaenses dos clones de cana-de-açúcar RB925268 e RB945950, e compará-los com isolados das variedades RB72454 e SP86155 do Estado de São Paulo. Foram observadas variações na severidade, e no tempo necessário para a manifestação dos sintomas nas plantas inoculadas com cada isolado. Através da reação de RT-PCR com oligonucleotídeos para o SCMV, obteve-se a amplificação de fragmentos com aproximadamente 900 pb da ORF codificadora da protéica capsidial. O padrão de RFLP resultante do tratamento dos produtos de RT-PCR com a enzima HinfI revelou variações na seqüência de nucleotídeos, indicando que possam existir diferentes estirpes do SCMV entre os isolados.

Detection and serological relationships of cymbidium mosaic potexvirus isolates

Twenty-two isolates of Cymbidium mosaic virus (CyMV) were isolated from 35 orchid plants suspected of being infected with CyMV. Among the three methods used for detecting CyMV, immunoelectron microscopy (IEM-1) was shown to be the most sensitive method, being able to detect the virus in 71.43% of suspected CyMV-infected plants while the electron microscopic method and the indexing plant method could detect 51.43 and 42.86%, respectively. Out of 12 symptomless plants investigated, 25% were found by IEM-1 method to be infected with the virus. Purified CyMV were flexuous rods having lengths between 470-490 nm. A few end-to-end aggregates were also observed and the 280 260 absorbance ratios were from 0.884 to 0.929. The yield of CyMV was 31.07 to 44.09 mg per kg of Datura leaves. Antibodies against purified CyMV D2 were produced in rabbits and hens. The antibody titers in the yolk and sera of hens indicated that 0.5 mg of virus per immunization efficiently generated an abundant supply of IgY in the yolk, however 1 mg of virus per immunization gave a stronger immune response in both sera and yolk. The average yields of IgY were 6.5 +/- 0.6 and 9.4 +/- 0.9 mg/ml of yolk in the group that received 0.5 mg and the group that received 1.0 mg of the virus, respectively. Positive ELISA reactions were observed in 18 and 20 of 22 CyMV isolates when detected with rabbit IgG and IgY, respectively, demonstrating that those isolates were serologically related and the ELISA reactions were shown to be stronger with IgY than those with rabbit IgG in most isolates. The degree of reaction between the CyMV isolates, O(2) and O(4), and IgY was less than that of the other isolates. The two isolates, D(6) and Cat(6), gave negative reactions to rabbit IgG. The results of ELISA assays showed that the homologous serological reaction was not consistently stronger than the heterologous one. Twelve isolates out of twenty-two gave stronger reactions than the homologous antigen (CyMV D(2)) when IgY was used as the detecting antibody while nine isolates gave stronger reactions when using rabbit IgG. No reactions were observed with other plant viruses and plant proteins from healthy Datura.

Etiology of Sweet Potato Chlorotic Dwarf Disease in Argentina

Chlorotic dwarf (CD), the most important disease in the sweet potato-producing regions of Argentina, is caused by the synergistic combination of two aphid-transmitted potyviruses with a whitefly-transmitted crinivirus. Sweet potato feathery mottle virus, sweet potato mild speckling virus, and a crinivirus (serologically related to sweet potato chlorotic stunt virus) were associated with CD. The synergistic combination of these three viruses reproduced the disease.

Quantification of recombinant core-like particles of bluetongue virus using immunosorbent electron microscopy

Immunosorbent electron microscopy was used to quantify recombinant baculovirus-generated bluetongue virus (BTV) core-like particles (CLP) in either purified preparations or lysates of recombinant baculovirus-infected cells. The capture antibody was an anti-BTV VP7 monoclonal antibody. The CLP concentration in purified preparations was determined to be 6.6 x 10(15) particles/l. CLP concentration in lysates of recombinant baculovirus-infected cells was determined at various times post-infection and shown to reach a value of 3 x 10(15) particles/l of culture medium at 96 h post-infection. The results indicated that immunosorbent electron microscopy, aided by an improved particle counting method, is a simple, rapid and accurate technique for the quantification of virus and virus-like particles produced in large scale in vitro systems.

Expression and assembly of the potato virus Y (PVY) coat protein (CP) in Escherichia coli cells

A clone harboring the full-length cDNA of potato virus Y in a lambda-DASH vector under the control of a T7 promoter was introduced into Escherichia coli carrying the T7-RNA-polymerase gene on a plasmid. The viral coat protein was expressed and the product was of the same size as the corresponding mature protein in infected plants. Immunoelectronmicroscopy of transfected cell extracts revealed virus-like particles, indicating that the proteins involved in its processing and the viral coat protein retained their native activity.

An evaluation of some factors important for maximising sensitivity of plant virus detection by immuno-electron microscopy

We report the results of a comparison of the variations to the basic technique developed by Derrick and called 'serologically specific electron microscopy' by him. We have found that the reaction time of the antibody-coated grid with the virus preparation (virus acquisition time) is one of the key factors in determining the efficiency of the method at trapping virus particles. The lower the virus concentration, the longer the reaction time should be. The use of protein A to pretreat the grids before coating with antiserum did not appear to be of benefit under our conditions.

Evaluation of immunoadsorbent electron microscopic techniques for detection of Sindbis virus

Two immunosorbent electron microscopic techniques (ISEM), the protein A coated grid technique (PA-CGT) and the antibody coated grid technique (AB-CGT) were applied and evaluated for the detection of Sindbis virus from infected tissue culture fluids. At optimal conditions, the efficiency of trapping the virions was only about 1.5 higher with the PA-CGT as compared to the AB-CGT, but the PA-CGT was less dependent on the antiserum dilution used in the test. Both methods were suitable for quantitation experiments, since the number of virions trapped was proportional to the virus concentration. The influence of virus incubation time and temperatures, staining solutions, buffers and washing procedures on the trapping efficiency and specificity was further studied with the PA-CGT. Maximal trapping on coated grids was obtained after 3 h incubation of the virus. At room temperature, less debris was found on the grids, as compared to 37 degrees C, and the numbers of virions counted were only slightly lower. The optimal staining solution was alcohol uranyl acetate. The specificity of the PA-CGT was dependent on washing steps with phosphate buffered saline containing bovine serum albumin. With the standard procedure, at room temperature around 3 X 10(7) virions/ml (1 X 10(6) PFU/ml) were specifically detected in about 1.5 h.

Immunosorbent electron microscopy for detection of viruses

This chapter discusses the newer modifications of immunosorbent electron microscopy (ISEM) methods in both plant and animal virology. ISEM methods presented in the chapter include all the techniques where the “solid phase principle” is essential in a way similar to other solid phase immunoassays. These methods include (1) the antibody-coated grid technique (AB-CGT); (2) the protein A-coated grid technique (PA-CGT); (3) the protein A-coated bacteria technique (PA-CBT); and (4) the antigen-coated grid technique (AG-CGT). In all ISEM methods, one of the components of the system is adsorbed to a solid phase. In AG-CGT, PA-CGT, and AB-CGT, one of the reagents is adsorbed to an electron microscopic grid, while in PA-CBT protein A is naturally present on the surface of a bacterium that serves as a solid support. In ISEM methods, the viruses can be statistically evaluated and numerically expressed as number of virions per unit of area, and can, therefore, be statistically evaluated. Thus, these methods optimize the results of a test by quantifying the effects of the quality of the supporting grid, the time of adsorption, the pH, the presence of salts, and the type of staining. The ISEM also permits a detailed study of antigenic variations in the same genus of virus, and thus would visually pinpoint the type or strain differences.

Enhancement of the immunogenicity of the maize rough dwarf virus outer shell with the cross-linking reagent dithiobis(succinimidyl)propionate

Injection into rabbits of native or glutaraldehyde (GA)-treated intact particles of the fijivirus maize rough dwarf virus (MRDV) failed to yield antibodies to the outer shell of the virus. After fixation of the particles with the cross-linking reagent dithiobis(succinimidyl)propionate (DSP), antisera were obtained reacting with the outer shell of MRDV (both DSP-fixed and unfixed) to a titre of 1/1024 in immunoelectron microscopic decoration tests, but giving no reaction with another fijivirus, oat sterile dwarf virus, whose subviral particles are known to be unrelated to those of MRDV. Further fixation of the DSP-fixed particles with GA did not appear to enhance immunogenicity. Stabilization with DSP could have further application with viruses the instability of which renders them poor immunogens.

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.

Detection of rotavirus by serological trapping on antibody-coated electron microscope grids

A serological trapping technique for detecting rotaviruses is described which involves coating electron microscope grids with protein A and specific rotavirus antiserum. The presence of a layer of antibodies on the grid increases the number of rotavirus particles that can be visualized. Thirty-five crude fecal extracts from infants suffering from diarrhea were examined by the serological trapping technique and by standard electron-microscopy. When the specimens were deposited on antibody-coated girds, 71% of them were found to contain virus particles, compared with 20% on standard uncoated grids. The method is simple and rapid and does away with the need to concentrate the specimens.