Gravitational Biology 



expansion of human knowledge of phenomena in the atmosphere and space" 

 should be involved in these endeavors (NASA Act of 1958, Section 102[c][l]). 



The program is currently investigating four major topics: Cell Biology, Gravitational 

 Perception and Sensing, Developmental Biology, and Biological Adaptations. A 1-g 

 centrifuge has rarely been flown to provide a space-based control. Consequently, 

 few results noted thus far in space flight experiments can be unambiguously 

 attributed solely to microgravity rather than to radiation or other possible causes. 

 Much remains to be learned. 



Gravitational Aspects of Cell Biology 



All levels of biological organization appear to be sensitive to the influence of 

 gravity at forces greater than 1 g. Research in cell biology is designed to measure 

 this sensitivity and to understand the mechanisms by which cells respond to 

 gravity both as individuals and as components of multicellular organisms. 



Current research is directed toward a variety of objectives: investigating the effects 

 of gravity upon cell structure, division, differentiation, and metabolism; specifying 

 the causes of observed gravitational sensitivity, whether direct (intracellular in 

 origin), indirect (external or system causes), or a combination thereof; determining 

 whether interactions occur between gravity and other environmental factors, such 

 as light and ionizing radiation; examining whether observed changes in cell 

 structure and function are transient or permanent and whether adaptation occurs; 

 determining the scope and course of readaptation (if any) to 1 g; and investigating 

 the use of inflight analytical techniques, such as cell culturing and flow cytometry. 



Specific research under way includes studies of the role of amyloplasts as putative 

 statoliths in plant cells and their role in gravitropism, the interaction of otolithic 

 crystals and individual cells in mammalian vestibular systems that seem to 

 function as bioaccelerometers, the effects of gravity upon newly fertilized eggs and 

 their subsequent embryogenesis, the effects of gravity on hormone production at 

 the cellular level, bone cell turnover and growth, microbial growth and sensitivity 

 to antibiotics, and mechanochemical transduction of information between cells. 



Research conducted during space flight has shown that mitosis and cytokinesis in 

 plant cells seem to be affected by space flight, as is evidenced by slowed or 

 inhibited cell division. Whether this is due to the lack of a gravitational vector or 

 is a response to radiation or other possible environmental factors is, at present, 

 uncertain. 



Gravitational Perception and Sensing 



Plant and animal species have evolved a variety of gravisensory capabilities that 

 allow them to use the Earth's gravitational field for orientation during growth and 

 movement. Exposing research specimens to a range of gravitational environments 

 provides an opportunity to examine how different organisms perceive, sense, 

 transduce, and transmit information and respond to a gravitational field. 

 Researchers can also study the evolution of various gravity-sensing systems, the 



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