ИСТИНА

Modeling the behavior of biological objects in conditions of high radiation and attenuated geomagnetic field is important scientific problem, because modern space missions aim to reach different planets of solar system. The flux of cosmic rays outside the magnetic field of the Earth could be dangerous for space pioneers. It is a well-known fact that exposure to ionizing radiation leads to a decrease of vital activity of biological objects. In this work, we present a comparative study of the influence of space flight conditions and model experiments on the photosynthetic apparatus of cyanobacterium Synechocystis sp. PCC 6803 (Synechocystis). The culture of wild type Synechocystis was launched into space on the satellite “Foton M4” and it orbited the Earth for 45 days. For modeling conditions of the space flight, we used a cyclotron U-120 SINP MSU, which yields accelerated helium nuclei with energy about 30.3 MeV. Changes in the structural and functional state of the photosynthetic membranes of cyanobacteria was evaluated by variety of optical methods, including fluorescence spectroscopy with picosecond time resolution (Simple-Tau 130, Becker & Hickl). It was found that the antenna complexes of Synechocystis - phycobilisomes are the most sensitive to ionizing radiation and the conditions of space flight, Figure 1. shows that the presence of cells under these conditions causes a significant decrease of the optical density in the region of phycobilisomes absorption. Simultaneously, we observed an increase in the intensity and fluorescence lifetime in the region of 660 nm (Figure 2), which is probably due to a violation of the integrity of phycobilisomes and decrease in the efficiency of excitation energy transfer within phycobilisomes and from phycobilisomes to the photosynthetic reaction center. The phycobilisomes of the cells exposed to radiation are functionally different due to almost complete absence of nonphotochemical quenching (NPQ) [1]. Space flight and high doses of ionizing radiation lead to inactivation of photosystem 2 (PS2). However, even after that some part of the culture remains viable and placing it into normal cultivation conditions leads to full restoration of all monitored parameters. Clarification of the mechanisms of such sustainability of cyanobacterial cells require additional research.