ABSTRACIWild type Gracilaria tik'ahiae, 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.The functional photosynthetic unit of 02-evolving plants is composed of large arrays of light-harvesting pigment-proteins which are associated with the reaction centers and electron transport chains of PSI and PSII. While the reaction centers, electron transport chains, and dark reactions of photosynthesis are probably very similar in the major plant groups, the lightharvesting systems are quite diverse. For example, the antennae pigments fucoxanthin and Chl c are found in the photosynthetic unit of the diatoms and brown algae. In the red algae, Cryptomonads, and cyanobacteria, the phycobiliproteins serve this function while Chl b functions in the green plants (22). These pigments along with the proteins which bind them are major '

Methods were developed for the isolation of large numbers of healthy protoplasts from two species of the agarophyte Gracilaria; G. tikvahiae McLachlan and G. lemaneiformis (Bory) Weber‐van Bosse. This is the first report of protoplast isolation and cell division in a commercially important, phycocolloid‐producing red seaweed, as well as for a member of the Florideophycidae. The optimal enzyme composition for cell wall digestion and protoplast viability consisted of 3% Onozuka R‐10, 3% Macerozyme R‐10, 1% agarase and 0.5% Pectolyase Y‐ 23 dissolved in a 60% seawater osmoticum containing 1.0 M mannitol. The complete removal of the cell wall was confirmed by several different methods, including electron microscopic examination, and the absence of Calcofluor White (for cellulose) and TBO (for sulfated polysaccharide) staining. Spontaneous protoplast fusion was observed on several occasions. Protoplast viability was dependent upon the strain and age of the parent material, as well as the mannitol concentration of the enzyme osmoticum. Cell wall regeneration generally occurred in 2‐6 days; cell division in 5‐10 days. Protoplast‐produced cell masses up to the 16‐32 cell stage have been grown in culture. However, efforts to regenerate whole plants have been unsuccessful to date.

Phycobilisomes were isolated from wild type Grcilaria tikvahiae and a number of its geneticafly characterized Mendelian and non-Mendelian pigment mutants in which the principal lesions result in an increase or decrease in the accumulation of phycoerythrin. Both the size and phycoerythrin content of the phycobilisomes are proportional to the phycoerythrin content of the crude algal extracts. In most of the strains examined, the structure and function of the phycocyanin-allophycocyanin phycobilisome cores are the same as in wild type. The phycobilisome architecture is derived from wild type by the addition or removal of phycoerythrin. The same pattern is observed for the phycobilisome of mos2 which contains a large excess of phycocyanin that is not bound to the phycobilisome. The single exception is a yellow, non-Mendelian mutant, NMY-1, which makes functional phycobilisomes composed of phycoerythrin and allophycocyanin with almost no phycocyanin. Characterization of the 'linker' polypeptides of the phycobilisome indicates that a 29 kilodalton protein is required for the stable incorporation of phycocyanin into the phycobilisome. Evidence is provided for the requirement of nuclear and cytoplasmic genes in phycobilisome synthesis and assembly. The symmetry properties of the phycobilisome are considered and a structural model for the reaction center II-phycobilisome organization is presented.Phycobilisomes are photosynthetic light-harvesting assemblages which are composed of pigment-protein complexes and are found associated with the photosynthetic membranes of the cyanobacteria and red algae (5). In many species, the phycobilisomes are quite abundant and fill much of the interthylakoidal space (5, 6). All This structural model is based on the dissociation kinetics of the isolated phycobilisome which demonstrate that PE is the most rapidly dissociated and therefore the most peripheral component ofthe phycobilisome (5), on the observation of six rods attached to negatively stained, isolated phycobilisomes from cyanobacteria and red algae (2,10,19,25), and by the isolation and characterization of PC:PE rods from a unicellular red alga (10).Excitation of either PE, PC, or APC in isolated intact phycobilisomes results in a major emission band with a maximum at 670 nm. The absorption and emission properties of the isolated biliproteins, the arrangement of the biliproteins in the phycobilisome, and the fluorescence emission properties of the isolated phycobilisomes all indicate that excitation energy is transferred from PE to PC to APC and emitted as fluorescence at 670 nm. In vivo, the phycobilisomes transfer excitations directly to Chl (5). This functional interpretation of the organization of the phycobilisome is supported by time-resolved fluorescence rise kinetics in isolated phycobilisomes and in vivo ( 16,20).The models of phycobilisome structure and function are derived from work on cyanobacteria and unicellular red algae. We sought to characterize the structural and functional organization of the phycob...

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