The sensitivity of lipid rafts in plant cells to the influence of simulated microgravity

1Kordyum, EL, 1Klymenko, O, 1Bulavin, IV, 1Zhupanov, IV, 1Vorobyova, TM, 2Ruelland, E
1M.G. Kholodny Institute of Botany of the National Academy of Sciences of Ukraine, Kyiv, Ukraine
2Institute of Ecology and Environmental Sciences, University Paris-Est Creteil, Paris, France
Space Sci.&Technol. 2018, 24 ;(4):51-60
Publication Language: Ukrainian
Plants as the sources of oxygen and food for astronauts have been recognized as a key component of Bioregenerative Life Support System. Biological membranes, first of all, the plasmalemma, can play a crucial role in the adaptation of plants to microgravity due to their properties and functions. The presence of functional domains called as the “lipid rafts” was proved in the plasmalemma. It is assumed that rafts modulate protein interactions and, thus, they are involved in numerous essential cell processes. The investigations of lipid rafts promote to understand the biochemical processes occurring in cell membranes in the norm and in response to stress.  
        Problematics of our study is the understanding a degree of gravisensitivity of basic cell processes and an adaptive potential of plants in the microgravity conditions that is extremely important for working out the technologies of plant cultivation in the  Bioregenerative Life Support System.  Objective of our study is to find out a degree of gravisensitivity of lipid rafts in plant cells on such indices as the composition and content of saturated and unsaturated fatty acids and sterols.
        Materials and methods are concerning with the pea seedlings, kind Bersek, which were growing during 6 days in the stationary conditions and under slow horizontal clinorotation. On the 7th day, the seedlings were cut off from the roots. A raft fraction was obtained from the plasmalemma fraction isolated from roots using a centrifuge “Оptima L-90K“. The raft fraction was investigated by the methods of electron microscopy with an electron microscope JEM 1230 (“JЕОL”, Japan) and gas chromatography using an apparatus HRGC 5300 (“Carlo Erba Instruments”, Italy). 
          It was shown that rafts look like thin ribbons 80–100 nm long and 6–13 nm wide. Under clinorotation, the qualitative composition of main fatty acids in the raft fraction did not change; the differences were found in their percentage. Under the influence of simulated microgravity, the content of saturated fatty acids was greater than the content of unsaturated fatty acids as well as it has been increased, especially a palmitic acid, both in the raft fraction and in the stationary control. Thereafter, a percent of unsaturated fatty acids decreased, especially arachidonic acid. A decrease in the content of monoenic unsaturated fatt acids in comparison with control was noted too. Content of a tetraenoic fatty acids has a highest percentage among polyene fatty acids. Under clinorotation, a percent of the cholesterol in the raft fraction has been increased 7 times in comparison with control.
            For the first time, the essential increase in the content of cholesterol and some saturated fatty acids in lipid rafts under clinorotation has been shown. This may indicate a raft rigidity strengthening under simulated microgravity that can lead to changes in plasmalemma permeability, selectivity and activity of corresponding proteins.   A higher raft rigidity occurs against the backdrop of maintaining microviscosity of the membrane itself at the normal level. It is proposed to emphasize attention on the research of the role of lipid rafts in plant cell gravisensitivity.
Keywords: clinorotation, fatty acids, Pisum sativum, plasmalemma, rafts, sterols