Effects of microgravity on the structure and function of plant cell walls.

The structural, biochemical, cytofluorimetric and electron cytochemical features of the cell walls of higher plants grown under weightlessness and simulated microgravity are described. Space flight and laboratory clinostatic experiments with plants show that the ultrastructure of the cell wall, its polysaccharide composition, and metabolic organization depend on the type of tissue and the duration of weightlessness. Horizontal clinostating that reproduced the biological effects of microgravity on cell walls showed that the structure of the external walls of the epidermis of aboveground organs is very sensitive to microgravity. Various responses occur in the primary and secondary walls under weightlessness and clinorotation: rearrangement of cell walls and organelles and changes in the content of cellulose, lignin, callose, and hemicelluloses. It is shown that plant cell wall changes under microgravity are connected with changes in cellulase, pectinase, and peroxidase activity and a change in the calcium balance in the cytoplasm and apoplast.