ИСТИНА

To protect photosynthetic apparatus from intense solar radiation cyanobacteria developed water-soluble photoactive Orange Carotenoid Protein (OCP), which contains carotenoid molecule 3’-hydroxyechinenone (hECN). It is responsible for non-photochemical quenching (NPQ) of fluorescence of light harvesting antenna. OCP converts in to quenching red form under blue-green illumination. In this work, we show that OCP may be converted in to the red form under exposure to ionizing radiation. It was found that molecules of hECN in OCP are bleached by ionizing radiation. Similar effects were observed in experiments where photosensitizer (aluminum phthalocyanine, AlPC [1]) produced singlet oxygen in solution of OCP. However besides overall decrease of carotenoid concentration upon bleaching we observed an increase of optical density at 550 nm indicating formation of the red form of the OCP. Our observations reveal that oxidative stress may also trigger conversion of OCP in to the red form which may also happen in vivo, resulting activation of protective mechanisms. Probably such activation of OCP in the dark may be useful to prevent possible effects of high light stress.