Kalinina I. Root tip cell growth and differentiation in Brassica rapa seedlings under microgravity and clinorotation conditions

The thesis is devoted to questions on gravisensitivity of plant cells not specialized to gravity perception. To elucidate the gravisensitivity of root apex cells during their growth and differentiation, we investigated the ultrastructural organization and cytoskeleton in cells of root growth zones in Brassica rapa and Arabidopsis thaliana (stably transformed lines GFP-MAP4 and GFP-ABD2) seedlings grown at 1g, under horizontal clinorotation (2rpm) and in real microgravity on board the shuttle "Columbia" in the frame of the Collaborative US/Ukrainian Experiment during STS-87 (1997 y.). Clinorotation was used to simulate some effects of microgravity. Methods of immunocytochemistry, light, electron and confocal microscopy were used. The distal elongation zone has been shown to be the most sensitive to microgravity and clinorotation in comparison with other root growth zones. We showed that spaceflight conditions induced a wider range of rearrangement in the organelle ultrastructure than clinorotation. Somechanges in cell ultrastructure in microgravity, especially increasing the volume of ER-bodies, which represent dilatation of granular endoplasmic reticulum, indicate its stress influence. In microgravity and under clinorotation, an acceleration of cell differentiation occurs, that is revealed in an appearance of lociniate nuclei in meristematic cells in the distal elongation zone. An appearance of disoriented cortical microtubules in cells of the distal elongation zone in B. rapa and A. thaliana (GFP-MAP4) roots under clinorotation has been observed. The significant decrease in a cell length in the central elongation zone, i.e. declining in an anisotropic growth, is suggested to connect with microtubule disorientation in the distal elongation zone. Based on in vivo experiments with A. thaliana (GFP-MAP4) we present data that disoriented microtubules appeared in the distal elongation zone under clinorotation are hypersensitive to oryzalin, that indicates increasing the rate of their dynamic turnover. A dynamics of cortical microtubule is assumed to cause high sensitivity of the distal elongation zone to altered gravity.