EVIDENCE FOR A COMMON ORIGIN OF CHLOROPLASTS WITH LIGHT-HARVESTING COMPLEXES OF DIFFERENT PIGMENTATION

THE red algae (Rhodophyta), which like cyanobacteria have only chlorop hyll a and use phycobilisomes for light-harvesting1,2, are often consi dered to have originated independently of other photosynthetic eukaryo tes, namely the chlorophyll a/b-containing Chlorophyta and the chlorop hyll a/c-containing Chromophyta3. Here we report that the red alga Por phyridium cruentum has a chlorophyll a-containing antenna complex func tionally associated with photosystem I, and that polypeptides of this antenna complex are immunologically related to those of higher-plant c hlorophyll a/h complexes and to those of chromophyte fucoxanthin-chlor ophyll a/c antenna complexes. This establishes a clear link between or ganisms containing phycobilisomes and those containing chlorophyll-bas ed light-harvesting complexes and shows that these antennae can co-exi st in the same organism. Furthermore, it suggests that the light-harve sting proteins of all photosynthetic eukaryotes had a common origin an d supports the idea that chloroplasts had a common ancestor4-6.