Migration of the Fungal Protein Cryptogein within Tobacco Plants.

Cryptogein (CRY), a protein secreted by Phytophthora cryptogea, causes necrosis on tobacco (Nicotiana tabacum) plants at the site of application (the stem or the roots) and also on distant leaves. Autoradiography of plantlets after root absorption of radioiodinated CRY demonstrated a rapid migration of the label to the leaf lamina via the veins. Using an anti-CRY antiserum, a CRY-related antigen was detected in the stem and leaves of CRY-treated plants at a distance from the site of application. This antigen had the same molecular weight as CRY and was detected in the leaves as early as 1 hour after stem treatment, i.e. long before necrosis was detectable. The antigen was also detected in plants inoculated with P. cryptogea. The distant location of the necrosis induced by the fungus or by CRY can be ascribed to the migration of this protein, which is toxic to tobacco cells. It is proposed that CRY, which also elicits defense reactions in tobacco, might contribute to the hypersensitive response of tobacco to P. cryptogea.

Serotype specificity of monoclonal antibodies to cucumber mosaic virus.

Ten monoclonal antibodies (McAbs) against cucumber mosaic virus (CMV) have been raised from fusion experiments performed after immunizing mice with different CMV antigens. Their reactivities with members of the three CMV serotypes, CMV-DTL, CMV-ToRS, and CMV-Co were tested in a double antibody sandwich format of enzyme immunosorbent assay (ELISA). Several of the McAbs were specific for different members of the CMV-DTL and CMV-ToRS groups while two allowed the detection of CMV-Co. By using a mixture of two McAbs, any member of the three major CMV serotypes could be detected in infected plant sap. One of the antibodies made it possible to discriminate between subunits and whole virions of CMV-D when it was used in ELISA simultaneously as coating antibody and as biotin-conjugate. McAbs were shown to be useful for quantifying the amount of CMV present in plant sap.

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.