[Response of siphoneal alga (Vaucheria sessilis) to the gravity factor]. / Reaktsiia sifoneal'noi vodorosli (Vaucheria sessilis) na gravitatsionnoe vozdeistvie.

Growth and development of siphonal alga Vaucheria sessilis under changed gravity and the role of cytoskeletal structures in gravitational response were studied. Hypergravity (3 g) and "hypogravity" were generated by slow clinostating at 7-8 rev/min and rapid clinostating at 35, 70, 135 rev/min, respectively. The experiments in microgravity were flown aboard biosatellite Bion-11. As was shown, V. sessilis responded to changed gravity by inhibition of rate of growth and increasing the number of nuclei in the strand as a result of activation of mitotic processes. Modulation of the course of the gravitational response with anticytoskeletal agents points to involvement of the cytoskeleton. The cortical circuit of actin microfilaments and the cytoplasm stream directed by this structure appear to be the most sensitive to changes in gravity. Gravity-sensitive V. sessilis is another promising object of research in the field of gravitational biology.

[Peculiarities of growth and morphogenesis of syphoneal alga vaucheria sessilis in microgravity]. / Osobennosti rosta i morfogeneza sifoneal'noi vodorosli vaucheria sessilis v usloviiakh mikrogravitatsii.

The space experiment was aimed at studying the dependence on the gravity of intracellular processes in an autotrophic organism deprived of pronounced gravitropisms and gravitaxis. The experiment demonstrated an immediate gravitational effect on intercellular processes involving the syphoneal alga Vausheira sessilis cytoskeleton. In the absence of the force of gravity algal growth and morphogenesis are inhibited more significantly than under the condition of the Earth's gravity.

Influence of modified gravity on growth and structure of Vaucheria sessilis (Xanthopyceae).

The constant presence of gravity force in the evolution of life on Earth caused the adaptation for its pressure and dependence of growth and morphogenesis of high plants on gravity, and appearance of gravitaxises of unicellular organisms. The modern investigations demonstrated the ability even of prokaryotic organisms for sensitivity of gravity modifications Erdmann et al., 1997). Object of current investigation was siphonaceous alga Vaucheria sessilis with branching thallome without septs. Vaucheria does not demonstrate gravitropic reaction, and does not possess statolite-like structure. It is important to note that graviresponse of such kind of objects was under investigation for the first time. The definite structure of cytoskeleton permits the functions of cytoskeleton elements to be analyzed in course of graviresponse. Siphonaceous algae are new and promising objects in gravitational cell biology. This investigation was intended to compare the graviresponse of Vaucheria detected on different experimental models of modified gravity.

The position of nuclei and the role of cytoskeleton in graviresponse of siphonaceous algae Vaucheria sessilis.

Gravity has always been present during evolution. Through the process of natural selection, contemporary organisms could show evidence of having turned gravity to their advantage as an adjunct to development. In recent time great success has been achieved in description and analysis of gravitaxis mechanism of algae Chara (Sievers et. al., 1991) and Euglena (Hader et. al., l990). The aim of present investigation was the demonstration of gravity-dependent growth and development of algae without distinct gravitaxis and gravitisensor organelles, such as statoliths and amyloplasts.

Peculiarities [correction of Peculiarites] of the graviperception and graviresponses [correction of graviresponces] in some unicellular eukaryotic organisms.

NASA: The growth and ultrastructure of Vaucheria sessilis, a siphonaceous alga, were studied during simulated weightlessness using a clinostat and during hypergravity on a centrifuge. Observations, including abnormalities in sporulation and changes in the distribution of nuclei, are presented and discussed.^ieng