An Evolutionary Tree Based on Monoclonal Antibody-Recognized Surface Features of a Plastid Enzyme (5-Aminolevulinate Dehydratase)

We describe and discuss an evolutionary tree derived from data which were obtained using monoclonal antibodies. Monoclonal antibodies (see e.g. Köhler and Milstein, N ature 256, 495 (1975)) were prepared against 5-aminolevulinate dehydratase (ALAD) from spinach (Spinacia oleracea) and enabled us to study 13 different ALAD antigenic determinant characters from origins as diverse as algae, mosses, ferns, gymnosperms and angiosperms. The results show that a dendrogram based on these characters is largely in accord with evolutionary trees based on classical characters. Species, such as Chara or Gnetum, whose system­ atic positions are doubtful, are separated from their alleged relatives. ALAD from the photosynthetic bacterium Rhodopseudomonas spheroides showed antigenic similarities with the plastid ALAD enzyme from spinach, while none of the antibodies against the spinach enzyme reacted with ALAD from the blue-green alga Nostoc muscorum. This finding is relevant to the problem of the origin of plastids and shows that monoclonal antibodies may also provide a new approach to the solution of this problem. The results imply that monoclonal antibodies will prove themselves efficient tools for taxonomic or evolutionary studies.