Previous studies on growth and development during spaceflight had incicated that the transition from vegetative to reporductive growth was particularly difficult for plants. Our objective has been to study how the spacflight environment impacts the different steps in plant reproduction. This goal has been pursued in two general ways: by using plants that had been pre-grown to the flowering stage on earth, and by using plants that developed completely on orbit. Our objectives havs been met by a combination of experiments that required essentially no crew time on orbit, and those that required an extensive commitment of crew time. The plants chose for the studies were closely related memberse of the family Brassicxacease: Arabilidopisis thaliana and Brassica rapa. In a series of short-duration experiments with Arabidopsis on the space shuttle we found that depletion of carbon dixode in closed chambers resulted in aborted development of both the male and female reporoductive apparatus in microgravity. Normal development was restored by addition of carbon dioxide or by providing air flow. A subsequent shuttle experiment with Brassica utilizing hardware that provides a vigorous air flow confirmed embryo development following pollination o orbit. BSrasica plants grown from seed on the Mir space station produced seed that germinated and grew when replanted on orbit. Future experiments will determine effects of multiple gnerations in space.
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