POLLEN AND OVULE DEVELOPMENT IN ARABIDOPSIS-THALIANA UNDER SPACEFLIGHT CONDITIONS

The development of pollen and ovules in Arabidopsis thaliana on the sp ace shuttle 'Endeavour' (STS-54) was investigated. Plants were grown o n nutrient agar for 14 days prior to loading into closed plant growth chambers that received light and temperature control inside the Plant Growth Unit flight hardware on the shuttle middeck. After 6 days in sp aceflight the plants were retrieved and immediately dissected and proc essed for light and electron microscope observation. Reproductive deve lopment aborted at an early stage. Pistils were collapsed and ovules i nside were seen to be empty. No viable pollen was observed from STS-54 plants; young microspores were deformed and empty. At a late stage, t he cytoplasm of the pollen contracted and became disorganized, but the pollen wall developed and the exine appeared normal. The tapetum in t he flight flowers degenerated at early stages. Ovules from STS-54 flig ht plants stopped growing and the integuments and nucellus collapsed a nd degenerated. The megasporocytes appeared abnormal and rarely underw ent meiosis. Apparently they enlarged, or occasionally produced a dyad or tetrad, to assume the form of a female gametophyte with the single nucleus located in an egglike cell that lacks a cell wall. Synergids, polar nuclei, and antipodals were not observed. The results demonstra te the types of lesions occurring in plant reproductive material under spaceflight conditions.