Abstract
A simple and highly sensitive radioimmunosorbent assay (RISA) for the detection of plant viruses is described. The RISA procedure is a microplate method based on the principle of double-antibody sandwich and follows essentially the protocol of the enzyme-linked immunosorbent assay (ELISA) (Clark & Adams, 1977), with the exception that 125I-labelled γ-globulin is substituted for the γ-globulin enzyme conjugate; the bound 125I-γ-globulin is dissociated by acidification from the double-antibody sandwich. The radioactivity is proportional to virus concentration, and cauliflower mosaic virus (CaMV) and lettuce mosaic virus (LMV) could be detected at concentrations as low as 5 and 2 ng/ml, respectively. Direct evidence of the adverse effects of conjugation with enzyme on the binding abilities of antibodies is presented. The RISA procedure should prove valuable with viruses for which the ELISA values are too low to be dependable.