9632087 Moroney Unicellular algae, including Chlamydomonas reinhardtii, have the capacity to concentrate carbon dioxide internally, allowing these organisms to grow photoautotrophically at very low external carbon dioxide concentrations. This carbon dioxide concentrating mechanism is inducible; it is present only in cells that have been grown with limiting carbon dioxide conditions. Dr. Moroney has shown that cells with the carbon dioxide concentrating mechanism have the low carbon dioxide-inducible polypeptide, LIP-36, present in the chloroplast envelope. He also has identified six genes that are specifically induced by growth on low carbon dioxide. Two of these genes, 1113 ans 215, encode putative transmembrane proteins. Recently he has obtained the gene encoding LIP-36 and has identified a gene encoding an internal carbonic anhydrase. In this award, Dr. Moroney will study the carbon dioxide concentrating mechanism in C. reinhardtii by using three approaches. In the first approach he will continue to characterize some of the genes and proteins identified. The second approach will be to measure inorganic carbon transport using chloroplast envelope vesicles in collaboration with Dr. Richard E. McCarty, Johns Hopkins University. The third approach will be to use cellular fractionation and immunolocalization to localize rubisco and the newly discovered carbonic anhydrase within the chloroplast of C. reinhardtii. The characterization of the proteins of this transport system will increase our understanding of the low carbon dioxide adjustment in algae and the role of the chloroplast in this photosynthetic adaptation. Algal photosynthesis contributes a major portion of the earth's energy cycle. Studies of its underlying mechanisms will contribute to our understanding of global change.
