Okadaic acid antibody localizes to chloroplasts in the DSP-toxin-producing dinoflagellates Prorocentrum lima and Prorocentrum maculosum

Thin sections of Prorocentrum lima (Ehrenberg) Dodge and Prorocentrum maculosum Faust, two dinoflagellates known to produce diarrhetic shellfish poisoning (DSP), were probed with a monoclonal antibody targeted against okadaic acid (OA), the primary toxin in DSP outbreaks. The antibody localizes primarily to chloroplasts and pyrenoids and, to a lesser degree, cellular Iysosomes. Controls on the primary antibody lack labelling, as do controls done on a non-producer of toxin, Prorocentrum micans Ehrenberg, and a paralytic shellfish poison (PSP) producer, Alexandrium tamarense (Lebour) Balech. OA is likely to be produced by the chloroplasts of the cell and its compartmentalization in plastids may explain why producer cells are unaffected by the toxicity of OA to eukaryotic cytoplasmic phosphatases.