CHARACTERIZATION AND BIOLOGICAL IMPLICATIONS OF SCYTONEMIN, A CYANOBACTERIAL SHEATH PIGMENT1

摘要: Scytonemin, the yellow-brown pigment of cyanobacterial (blue-green algal) extracellular sheaths, was found in species thriving habitats exposed to intense solar radiation. Scytonemin occurred predominantly sheaths outermost parts or top layers mats, crusts, colonies. appears be a single compound identified more than 30 cyanobacteria from cultures and natural populations. It is lipid soluble has prominent absorption maximum near-ultraviolet region spectrum (384 nm acetone; ca. 370 vivo) with long tail extending infrared region. Microspectrophotometric measurements transmittance pigmented quenching ultraviolet excitation phycocyanin fluorescence demonstrate that effective shielding cells incoming near-ultraviolet-blue radiation, but not green red light. High light intensity (between 99 250 μmol photon · m−2· S−1, depending on species) promoted synthesis scytonemin cyanobacteria. In cultures, high caused reduction specific content Chl phycobilins, increase ratio total carotenoids a, increase. UV-A (320–400 nm) radiation very eliciting synthesis. production physiological due mere photochemical conversion. These results strongly suggest constitutes an adaptive strategy photoprotection against short-wavelength irradiance.