Life Sciences in the Space Program 



operation of these systems in microgravity and the neurological component of 

 gravity sensing. 



Plant Gravisettsing. Plant responses to changes of the gravitational vector are 

 exhibited by alterations in the location and rate of growth. Flight and ground 

 experiments have shown that electrical and ionic currents are detectable as early 



responses to gravity and that 

 calcium ions are probably 

 involved in the transduction of 

 a gravitational stimulus. Results 

 from space experiments suggest 

 that plant shoot growth may 

 be directed by both gravity and 

 light, whereas root growth may 

 respond solely to a gravita- 

 tional force. 



Current research efforts are 

 directed toward understanding 

 what occurs at the cellular level 

 in the perception of gravita- 

 tional fields (with emphasis on 

 the role of calcium and 

 hormonal messengers and of 

 intracellular organelles as 

 gravity sensors), the gravitropic 

 responses in stems and roots 

 (and the role of gravity in 



These pine seedlings were flaunt on Spacelab 2 (STS 51-F), July 29-August 6, 1985, and 

 photographed after the mission. The miniature greenhouses, called Plant Growth Units, 

 allow investigators to monitor the effects of microgravity on the direction of plant 

 growth and on the formation of lignin, a woody substance in the plants that allows 

 them to grotc upward against the pull of gravity. 



apical dominance), and the use of clinostats as a ground-based means of 

 simulating variable levels of hypogravity. 



Animal Gravisensing. Animals are capable of sophisticated responses to 

 environmental stimuli by virtue of a complex nervous system integrated with a 

 musculoskeletal system. The Space Biology Program has concentrated on 

 understanding the role gravity has played in shaping the functional organization 

 of animal gravity sensing and organs (bioaccelerometers). Ground-based research 

 focuses on this problem by studying the morphology and physiology of gravity 

 sensors of representative species of animals, both invertebrate and vertebrate, to 

 better understand how gravity sensors process information . Ground-based studies 

 are under way to determine the mechanisms of transduction, including ionic as 

 well as mechanical processes, and of transmission of information from the 

 receptors to the central nervous system. Although work on neurotransmitters and 

 on neural coding is not presently supported, these areas are within the scope of 

 information processing and should be undertaken. 



Ground-based research also employs computer-based, three-dimensional 

 reconstruction of gravity sensing and organs of mammals. This research, when 

 combined with results from physiological and neurochemical investigations, can 



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