title: Stabilization and modulation of the phycobilisome by calcium in the calciphilic freshwater red alga Bangia atropurpurea.
abstract: The bangiophycean filamentous red alga Bangia atropurpurea is distributed in freshwater habitats such as littoral and splash zones of lakes or rapid currents distant from the sea. In these habitats, the distribution and growth of this alga appear to be related to hard water rich in calcium ions. To characterize the eco-physiological properties of this calciphilic red alga, we examined the effects of long-term and short-term Ca(2+) depletion on photosynthetic growth of the thallus and on the phycobilisome. Long-term culture experiments suggested that higher Ca(2+) concentrations (>50mgL(-1)) were required to sustain thallus growth and pigmentation of cells. In short-term Ca(2+)-depletion treatments, fluorescence derived from phycoerythrin (PE) fluctuated, although the absorption spectra of the thalli did not change. After 30 min of Ca(2+) depletion, the fluorescence lifetime of PE became markedly longer, indicating that the energy transfer from PE to phycocyanin (PC) was suppressed. The fluorescence lifetime of PE returned to its original value within a short time after 4h of Ca(2+) depletion, however, energy transfer from PE to PC was still suppressed. This suggested that the excitation energy absorbed by PE was quenched during prolonged Ca(2+) depletion. The efficient energy transfer from PC and allophycocyanin were unchanged during these treatments.
authors.affiliation: Molecular Photoscience Research Center, Kobe University, Kobe, Hyogo, Japan. filia@mac.com
authors.forename: Makio
authors.initials: M
authors.lastname: Yokono
authors.forename: Hiroko
authors.initials: H
authors.lastname: Uchida
authors.forename: Yuzuru
authors.initials: Y
authors.lastname: Suzawa
authors.forename: Seiji
authors.initials: S
authors.lastname: Akiomoto
authors.forename: Akio
authors.initials: A
authors.lastname: Murakami
mesh_terms: D002118:Calcium / Q000494:pharmacology*; D002478:Cells, Cultured; D004735:Energy Transfer / Q000187:drug effects; D005453:Fluorescence; D005618:Fresh Water; D008954:Models, Biological; D010788:Photosynthesis; D045524:Phycobilisomes / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism*; D055503:Protein Multimerization / Q000187:drug effects*; D055550:Protein Stability / Q000187:drug effects; D000461:Rhodophyta / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism / Q000648:ultrastructure; D012623:Seawater; D013057:Spectrum Analysis
chemical_list: D045524:Phycobilisomes; D002118:Calcium