SPACEFLIGHT EXPOSURE EFFECTS ON TRANSCRIPTION, ACTIVITY, AND LOCALIZATION OF ALCOHOL-DEHYDROGENASE IN THE ROOTS OF ARABIDOPSIS-THALIANA

Although considerable research and speculation have been directed towa rd understanding a plant's perception of gravity and the resulting gra vitropic responses, little is known about the role of gravity-dependen t physical processes in normal physiological function. These studies w ere conducted to determine whether the roots of plants exposed to spac eflight conditions may be experiencing hypoxia. Arabidopsis thaliana ( L.) Heynh. plants were grown in agar medium during 6 or 11 d of spacef light exposure on shuttle missions STS-54 (CHROMEX-03) and STS-68 (CHR OMEX-05), respectively. The analysis included measurement of agar redo x potential and root alcohol dehydrogenase (ADH) activity, localizatio n, and expression. ADH activity increased by 89% as a result of spacef light exposure for both CHROMEX-03 and -05 experiments, and ADH RNase protection assays revealed a 136% increase in ADH mRNA. The increase i n ADH activity associated with the spaceflight roots was realized by a 28% decrease in oxygen availability in a groundbased study; however, no reduction in redox potential was observed in measurements of the sp aceflight bulk agar. Spaceflight exposure appears to effect a hypoxic response in the roots of agar-grown plants that may be caused by chang es in gravity-mediated fluid and/or gas behavior.