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not peer-reviewed) is the author/funder. All rights reserved. No reuse allowed without permission.The copyright holder for this preprint (which was . http://dx.doi.org/10.1101/281386 doi: bioRxiv preprint first posted online Mar. 13, 2018; Cyanobacteria survived the Foton-M4 space mission 2 It is now generally accepted that cyanobacteria are responsible for production of oxygen, which led to the so-called "Great Oxygenation Event". Appearance of dioxygen in Earth's atmosphere resulted in formation of the ozone layer and the ionosphere, which caused significant reduction of ionizing radiation levels at the surface of our planet. This event not only increased biological diversity but also canceled the urgency of previously developed mechanisms of DNA protection, which allowed to survive and develop in harsh environmental conditions including exposure to cosmic rays. In order to test the hypothesis if one of the oldest organisms on Earth retained ancient protection mechanisms, we studied the effect of ionizing radiation (IoR, here: α-particles with a kinetic energy of about 30 MeV) and space flight during the mission of the Foton-M4 satellite on cells of Synechocystis sp. PCC6803. By analyzing spectral and functional characteristics of photosynthetic membranes we revealed numerous similarities between cells exposed to IoR and after the space mission. In both cases, we found that excitation energy transfer from phycobilisomes to photosystems was interrupted and the concentration of phycobiliproteins was significantly reduced. Although photosynthetic activity was severely suppressed, the effect was reversible and the cells were able to rapidly recover from stress under normal conditions.Moreover, in vitro experiments demonstrated that the effect of IoR on isolated phycobilisomes was completely different from such in vivo. These observations suggest that the actual existence and the uncoupling of phycobilisomes under irradiation stress could play specific role not only in photo-, but also in radioprotection, which was crucial for early stages of evolution and the development of Life on Earth.

The problem of environment protection has been attracting the attention of researchers all over the world, especially considering the increasing anthropo genic load. The state of plants can serve as a reliable indicator of environment pollution, because the sensi tivity of plants to many pollutants is often significantly higher than that of humans or animals [1,2]. The pol lutants cause significant changes in physiological bio chemical processes in the cells of the vegetative organs of plants, especially in the chloroplasts, where photo synthesis occurs. The disruption of cellular mem branes and shutting down of photosynthetic electron transport processes that lead to the oxygen release occurs [3,4]. The causes of the damage to the assimi lating organs of plant by exhaust fumes may be related to the fact that the majority of the fumes are strong oxidizers. Accumulation of exhaust fumes by plant cells predominantly in chloroplasts results in oxidative damage of cell membranes and other structures, as well as disruption of the use of light energy during pho tosynthesis, which, in turn, leads to the development of "photodynamic" oxidation processes. The disrup tion of photosynthesis causes a significant decrease in the ability of plants to make the environment healthier and to resist anthropogenic pressure.Considering the fact that plants are indicators of the health of the environment and that the physiolog ical state of plants is determined by the ability of the photosynthetic apparatus to absorb and transform the energy of light in the process of growth, the problem of the development of methods that characterize the state of the photosynthetic apparatus at each step of the transformation of light energy remains the most important [5][6][7]. The high sensitivity of the photo synthetic apparatus to damaging effects allows the use of methods that are based on measurements of the chlorophyll a fluorescence parameters for ecological studies. [4,[8][9][10][11][12]. Traditionally the relative variable fluorescence, F V /F M , which characterizes the effi ciency of photochemical energy transformation in photosystem II (PS II), is used for the determination of the efficiency of energy transformation in the pho tosynthetic apparatus [13][14][15]. However, it was recently suggested to use parameters for ecological studies that are calculated from the kinetics of the chlorophyll a fluorescence induction [6,9,16] con sidering the distribution of energy flows that are absorbed in PS II. The kinetics of light induction of the variable fluorescence (OJIP) measured in vivo within the millisecond range is characterized by three rise phases: OJ, JI, and IP, followed by the fluores cence decline phase, which mainly reflects the kinet ics of the transition of PS II centers from the open state with an oxidized Q A acceptor to the closed state with a reduced acceptor. Analysis of the fluorescence induction rise using the JIP test allows the elucidation of the major characteristics of the primary photosyn thetic processes that characte...

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