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Articles

Light-Harvesting System of the Red Alga Gracilaria tikvahiae¹

I. Biochemical Analyses of Pigment Mutations

Department of Biophysics and Theoretical Biology, The University of Chicago, Illinois 60637, Department of Biology, Barnes Laboratory, The University of Chicago, Illinois 60637, Atlantic Research Laboratory, National Research Council of Canada, Halifax, Nova Scotia, Canada

Wild type Gracilaria tikvahiae, a macrophytic red alga, and fourteen genetically characterized pigment mutants were analyzed for their biliprotein and chlorophyll contents. The same three biliproteins, phycoerythrin, phycocyanin, and allophycocyanin, which are found in the wild type are found in all the Mendelian and non-Mendelian mutants examined. Some mutants overproduce R-phycoerythrin while others possess only traces of phycobiliprotein; however, no phycoerythrin minus mutants were found. Two of the mutants are unique; one overproduces phycocyanin relative to allophycocyanin while the nuclear mutant obr synthesizes a phycoerythrin which is spectroscopically distinct from the R-phycoerythrin of the wild type. The phycoerythrin of obr lacks the typical absorption peak at 545 nanometers characteristic of R-phycoerythrin and possesses a phycoerythrobilin to phycourobilin chromophore ratio of 2.6 in contrast to a ratio of 4.2 found in the wild type. Such a lesion provides evidence for the role of nuclear genes in phycoerythrin synthesis. In addition, comparisons are made of the pigment compositions of the Gracilaria strains with those of Neoagardhiella bailyei, a macrophytic red alga which has a high phycoerythrin content, and Anacystis nidulans, a cyanobacterium which lacks phycoerythrin. The mutants described here should prove useful in the study of the genetic control of phycobiliprotein synthesis and phycobilisome structure and assembly.

³ R. S. A. was a Mellon Foundation Fellow during a portion of the research period. To whom reprint requests should be sent: Barnes Laboratory, 5630 S. Ingleside Avenue, Chicago, IL 60637.

¹ Supported by National Science Foundation grant PCM 78-10535, and in part by the Louis Block Foundation, The University of Chicago. National Research Council of Canada 22523.