Analysis of the spaceflight effects on growth and development of Super Dwarf wheat grown on the Space Station Mir

The hypothesis being tested is that Super Dwarf wheat, Triticum aestivum L. , plants in the Svet Greenhouse onboard the Russian Space Station Mir will complete a life cycle in spaceflight, providing that the environmental cond itions necessary for adequate growth on Earth are supplied. Twenty six seed s of wheat were planted in each of 2 rows of 2 root compartments for a tota l of 104 seeds in Svet. Germination rate at 7d was 56 and 73% on Mir and 75 and 90% in ground-based controls. Plants were grown throughout the whole c ycle of ontogenesis (123 d) with samples gathered at different times to val idate the morphological and reproductive stages of the plants. Young plants showed vigorous early seedling growth, with large biomass production, incl uding the formation of 280 floral spikes. Upon return to Earth, comparative analyses showed that the number of tillers and flowers per spikelet tt ere 63.2% and 40% greater, respectively, in Mir-grown plants than in the contr ols. By contrast, the stem length (52.4%), spike mass (49.2%) and length (2 3.1%), awn length (75.7%), number of spikelets per spike (42.8%) and number of seeds per spike (100% sterile) from Mir-grown plants were substantially less than the controls. Distribution of moisture and roots throughout the substrate was very good. All florets on Mir-grown spikes ceased development at the same stage of ontogeny. Lack of caryopses formation was attributed to male sterility occurring at different stages of staminal development. An thers failed to dehisce and pollen grains were smaller and shriveled compar ed to the controls, suggesting a chronic stress had occurred in the Svet gr owth chamber. Recent ground-based studies indicated that ethylene, which wa s measured at 0.3 to 1.8 mg.kg(-1) in the Mir, almost certainly could have induced male sterility in the wheat plants grown on the Mir.