The nonradioactive chloramphenicol acetyltransferase-enzyme-linked immunosorbent assay test is suited for promoter activity studies in plant protoplasts.

Four different promoters--the 35S, a double 35S promoter, and two different promoter fragments of the ribulose-bisphosphate carboxylase small subunit (rbcS)--were fused to the reporter gene chloramphenicol acetyltransferase (CAT) and transient expression studies were performed in potato protoplasts. Promoter strength was evaluated by using a nonradioactive CAT immunoassay not previously tested with plant cells. The activities of the rbcS promoters were 10-fold less than those of the 35S promoters. Unspecific reactions due to the immunoassay adopted were very low, and the sensitivity was in the range of that of other radioactive and nonradioactive reporter gene assays. The CAT-enzyme-linked immunosorbent assay test is a suitable nonradioactive alternative to test relatively weak promoters in plant systems.