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MICROSCOPIC ANALYSIS OF SWEETPOTATO ROOT TIPS PROPAGATED FROM STEM CUTTINGS MAINTAINED IN EITHER VERTICAL OR HORIZONTAL CLINOROTATION.   C.S. Williams, D.G. Mortley, C.E. Morris, C.F. Davis, S.D. Gamble and J.W. Williams.   Center for Food and Environmental Systems for Human Exploration of Space and the George Washington Carver Agricultural Experiment Station.  Tuskegee University, Tuskegee AL.

Although there has been some criticism of the system, clinostat rotation continues to be used as one of the major ground based models for simulation of microgravity.  Sweetpotato has been identified as one of the potential food crops for human planetary space exploration.  To that end, sweetpotato growth characteristics under simulated microgravity have important application to its growth in space.  Stem cuttings were placed in growth chambers rotating on clinostats with either vertical or horizonatal orientation for either 4, 7, or 14 days.  Root tips were collected and immediately placed in fixative (3% glutaraldehyde, 1.5% paraformaldehyde in 0.1M sodium cacodylate buffer).  Following overnight fixation, specimens were postfixed in 2% osmium tetroxide, en bloc stained with 0.5% uranyl acetate, dehydrated in a graded series of ethanol, and embedded in Spurr’s Medium (under vacuum).  Ultrastructural observations of the root tips, with emphasis on the statocytes, showed morphological and organizational changes, particularly in the starch-containing statoliths, within the cells consistent with the altered geotropism and direction of growth of the roots (vertical orientation  = “downward”; horizontal orientation = “upward” or “outward”).

(Supported by NASA:NAG10 0209 and USDA/CSREES ALX-PS-1.  Ultrastructural Facility support was provided by NIH/RCMI 5-G12RR03059.)