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Gravity as a biochemical determinantThe existence of obvious morphological and physiological changes in living systems exposed to altered gravity immediately informs us that prior changes have taken place in the chemistry of exposed cells, tissues and organs. These changes include transients that return more or less promptly to the norm when the system is restored to the terrestrial g-field. For example, altered serum hormone and electrolyte levels in man, which appear to reflect successful adaptation to the conditions of orbital weightlessness, disappear shortly after return to Earth. Other changes--in mineral and protein constituents of the skeletal system in man, and cell wall composition in plants--are more persistent or even permanent. Hypogravitational departures from the norm include not only "weightlessness" as achieved in orbit, but also experimental modes of compensation, on the clinostat or by flotation. These techniques are useful in the study of hypogravity but cannot replace fully the weightless environment. Plant ethylene and peroxidase both increase under orbital, clinostat and/or flotation conditions whereas 3-phosphoglyceraldehyde-dehydrogenase increases under orbital but not clinostat conditions; cytochrome reductase and malic dehydrogenase levels are affected by the clinostat, but not by actual weightless conditions. How do the altered organismal biochemistries induced by the centrifuge and the clinostat relate to one another? Does gravity operate on living systems as a continuous variable from 0 to superterrestrial values, or do deviations from g(earth) generate non-uniform, discontinuous stress responses, irrespective of sign? In plants, measurements of wall lignin content and peroxidase activity yield opposite answers. Given the limited data so far available we will consider the meaning of these contradictions.
Document ID
20040113390
Acquisition Source
Ames Research Center
Document Type
Reprint (Version printed in journal)
Authors
Siegel, S. M.
(University of Hawaii Honolulu, Hawaii 96822, United States)
Date Acquired
August 21, 2013
Publication Date
January 1, 1979
Publication Information
Publication: Life sciences and space research
Volume: 17
ISSN: 0075-9422
Subject Category
Aerospace Medicine
Funding Number(s)
CONTRACT_GRANT: NAS2-6624
CONTRACT_GRANT: NAS2-8687
Distribution Limits
Public
Copyright
Other
Keywords
Review
Review, Tutorial

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