| Abstract: | Monospecific, polyclonal antibodies raised against the apoprotein of the major light-harvesting pigment-protein of Phaeodactylum tricornutum Bohlin UTEX 646 were used to determine (1) whether this complex was common to the class Bacillariophyceae, whose members contain chlorophylls a and c and fucoxanlhin; (2) whether antigenically-related apoproteins were present in other chlorophyll c-containing groups, and (3) whether there was immunological homology with the light-hanvsting chlorophyll a/b protein of similar photosynthetic function in the Chlorophyta and vascular plants. We have used protein blotting techniques to show that antibodies against the two P. tricornutum light-harvesting complex polypeptides cross-reacted with one or two polypeptides of similar molecular weight (17–21 kD) in all ten diatom species examined, representing two orders and six families. No cross-reactivity was obtained with total membrane polypeptides from isolated representatives of three chromophyte algal divisions (Chrysophyta, Cryptophyta, Pyrrophyta), all of which contained chlorophyll c. No cross-reactivity was observed with membrane Polypeptides isolated from members of two classes of Chlorophte algae. These data suggest that the Bacillariophyceae may be monophyletic, and that the primary structure of the diatom light-harvesting complex is not closely related to pigment-protein complexes with similar function in other chlorophyll c-containing unicellular algal groups. Lastly, it may be possible to use the antibodies to the diatom light-harvesting polypeptides as specific markers for diatoms in natural phytoplankton assemblages. |
