Adaptative responses of tobacco callus cells to simulated microgravity by compensation.
Under the rotation-induced gravity compensation, growth rate of callus was repressed by about 44%. Its osmotic and water potential declined by about 22 and 27% respectively. The content of soluble sugar was enhanced by about 123% and that of K+ by about 25%. The permeability of plasmic membrane increased and the lipid peroxidation intensified. When the callus grown under clinostatting were subcultured and returned to stationary conditions, the growth rates and related physiological indications were restored again to or near to the level of the control (SC). Electron microscopic studies showed that nuclear membrane was invaginated so deeply that some of the nuclei were like a starfish. Rough endoplasmic reticulum was diminished. The smooth one observed on the surface of slices was lengthened by almost 8.9 times of the control (SC), the longest one reached to 42 micrometers. They were often concentrated in a corner of the cell. Some of them were rolled into tube-shapes. The amyloplasts were without starch grain. It is assumed that the responses of plant cell to microgravity may be a sort of tolerable unloading reaction on endomembrane system.