AbstractŠvegždienė D., Raklevičienė D., Koryzienė D., 2013: Space botany in Lithuania. I. Root gravisensing system formation during satellite "Bion-10" flight [Kosminė botanika Lietuvoje. I. Gravitaciją juntančių šaknų ląstelių formavimasis palydovo "Bion-10" skrydžio metu]. -Bot. Lith., 19(2): 129-138. the paper deals with the results of space experiment, which was carried out on an original automatically operating centrifuge "neris-5" on board of the satellite "Bion-10" in 1993. the peculiarities of gravisensing system formation in roots of garden cress (Lepidium sativum L.) seedlings grown in microgravity under simulated and natural gravity of 1g in space and on the ground, respectively, are presented. Quantitative study on the growth of root columella cells (statocytes), the state of their intracellular components, and the location of amyloplasts was performed by light and electron microscopy. the growth of statocytes in microgravity and under 1g in space did not differ significantly though the location of amyloplasts experienced significant changes: it depended on the gravity and cell position in columella. Instead of the concentration of amyloplasts at the distal cell region of roots grown under 1g, most plastids in microgravity-grown roots were accumulated at the centre of statocytes. the obtained data on the formation and state of intercellular plastids confirm the supposition that the environment of microgravity alters the metabolism of plant cells; however, its alterations are not fateful for the formation of gravisensing cells and for the growth of the whole root.

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In this study, the kinetics of gravitydependent movement of amyloplasts (statoliths) along root statocytes and hypocotyls (endodermis cells) has been analyzed and compared in order to testify cytoskeleton involvement in the displacement of statoliths in cress (Lepidium sativum L.) seedling statocytes. After 32 h of growth at 1 g or under a fast clinorotation (50 rpm), the seedlings were treated for 24 min as follows: exposition to clinorotation or 180 • inversion and the action of gravitational force in root tip or hypocotyl tip direction. Statolith displacement was studied by light microscopy on semithin longitudinal sections of hypocotyls and root caps, measuring the distance between the centre of plastids and morphological cell bottom. Considerable temporal differences have been determined between the kinetics of the longitudinal motion of amyloplasts in root and hypocotyl statocytes of 1-g seedlings upon exposition to fast clinorotation and inversion. In statocytes of both organs of seedlings grown under fast clinorotation, the gravity provoked displacement of statoliths in the direction of its action; however, the displacement was much faster in hypocotyl than in root statocytes. It has been assumed that the gravity-determined longitudinal transport of amyloplasts, both in hypocotyl endodermic cells and root statocytes of cress seedlings, is modulated by the cytoskeleton.

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Responses of cress (Lepidium sativum L.) seedling leaves to separate and simultaneous illumination with red (660 nm) and far-red (735 nm) light were studied under fast clinorotation (50 rpm) and usual gravity (1g) conditions. The monochromatic light emitting diodes (LEDs) have been used for illumination of seedlings from above. The growth and spatial orientation of leaves and the location of presumable gravisensors in petioles were analysed. Clinorotation in the dark promoted the radial expansion of leaf lamina and unfolding of leaves. It was shown that clinorotation in red light inhibited significantly the elongation of petioles as compared with that under the action of gravity force. Simultaneous red and far-red illumination promoted the growth of petioles under clinorotation, but did not affect the orientation of laminas, which remained the same as of the 1-g control ones. Red light, applied separately and simultaneously with farred light, guided the bending of laminas as well as the unfolding of leaf petioles in both usual and clinorotation conditions. Histological and cytological analyses of petioles revealed the presence of movable amyloplasts in endodermic cells in proximal region of petioles. Comparison of intracellular positioning of amyloplasts in petioles of leaves grown under clinorotation and the action of gravity allows a presumption that these plastids may be identified as gravisensors of garden cress leaves. The obtained data imply that clinorotation and exposition to monochromatic red light or simultaneous illumination by red and far-red light affect the elongation of petioles of cress seedling leaves. Spectral components guide the unfolding of laminas in a gravityindependent manner.