MODIFICATION OF REPRODUCTIVE DEVELOPMENT IN ARABIDOPSIS-THALIANA UNDER SPACEFLIGHT CONDITIONS

Reproductive development in Arabidopsis thaliana (L.) Heynh. cv. Colum bia plants was investigated under spaceflight conditions on shuttle mi ssion STS-51. Plants launched just prior to initiation of the reproduc tive phase developed flowers and siliques during the 10-d flight. Appr oximately 500 flowers were produced in total by the 12 plants in both the ground control and spaceflight material, and there was no signific ant difference in the number of flowers in each size class. The flower buds and siliques of the spaceflight plants were not morphologically different from the ground controls. Pollen viability tests immediately post-flight using fluorescein diacetate indicated that about 35% of t he pollen was viable in the spaceflight material. Light-microscopy obs ervations on this material showed that the female gametophytes also ha d developed normally to maturity. However, siliques from the spaceflig ht plants contained empty, shrunken ovules, and no evidence of pollen transfer to stigmatic papillae was found by light microscopy immediate ly post-flight or by scanning electron microscopy on fixed material. S hort stamen length and indehiscent anthers were observed in the spacef light material, and a film-like substance inside the anther that conne cted to the tapetum appeared to restrict the release of pollen from th e anthers. These observations indicate that given appropriate growing conditions, early reproductive development in A. thaliana can occur no rmally under spaceflight conditions. On STS-51, reproductive developme nt aborted due to obstacles in pollination or fertilization.