Cellular changes in wheat seedlings during orbital flight

Wheat seedlings in weightlessness aboard NASA Biosatellite 2 differ from ground control seedlings in mitotic count, cell length and nuclear volume as well as in orientation, starch grain distribution, organ length and malformations previously reported to COSPAR. Dividing cells are fewer in roots of orbited seedlings than in erect or clinostat ground controls. The greatest difference is among cells in early prophase. Root cells, proximal to the zone of cell division are longer in flight seedlings than erect or clinostat ground controls. As the roots are the same length, greater elongation compensates for the reduced rate of cell division. Volume of interphase nuclei in all seedling organs is increased by orbital flight. In clinostat controls, only nuclei of primary roots increase in size. Between 58 and 65 hours of age, nuclear volume in erect 1 g coleoptiles decreases; in flight seedlings it increases. Simulated launch vibration, alone or followed by growth on the clinostat, increases nuclear volume in some roots, but coleoptile nuclei do not respond as in flight seedlings. Thus, at the cellular level, orbital flight cannot be exactly duplicated by the clinostat whether preceded by vibration or not.