Reproductive Ontogeny of Wheat Grown on the Mir Space Station 981552
The reproductive ontogeny of ‘Super-Dwarf’ wheat grown on the space station Mir is chronicled from the vegetative phase through flower' development. Changes in the apical meristem associated with transition from the vegetative plhase to floral initiation and development of the reproductive spike were all typical of ‘Super Dwarf’ wheat up to the point of anthesis. Filament elongation, which characteristically occurs just prior to anthesis (during floral development stage 4) and moves the anthers through the stigmatic branches thus facilitating pollination, did not occur in the flowers of spikes grown on Mir. While pollen did form in the anthers, no evidence of pollination or fertilization was observed. Analysis of pollen idlentified abnormalities; the presence of only one nucleus in the pollen as opposed to the normal trinucleate condition is likely an important factor in the sterility observed in wheat grown on Mir. While development of spikes on tillers typically occurs later than that of spikes on the main stem, all flowers appear to be arrested at the same developmental point. This strongly suggests that an environmental stress such as drought was not responsible for the lack of anthesis; similarity with ground study results suggest that atmospheric contamination may have suppressed critical developmental processes during stage 4 of floral development.