Comparative floral development of Mir-grown and ethylene-treated, earth-grown Super Dwarf wheat

To study plant growth in microgravity, we grew Super Dwarf wheat (Triticum aestivum L.) in the Svet growth chamber onboard the orbiting Russian space station, Mir, and in identical ground control units at the Institute of Bio medical Problems in Moscow, Russia. Seedling emergence was 56% and 73% in t he two root-module compartments on Mir and 75% and 90% on earth. Growth was vigorous (produced ca. 1 kg dry mass), and individual plants produced 5 to 8 tillers on Mir compared with 3 to 5 on earth-grown controls. Upon harves t in space and return to earth, however, all inflorescences of the flight-g rown plants were sterile. To ascertain if Super Dwarf wheat responded to th e 1.1 to 1.7 mu mol . mol(-1) atmospheric levels of ethylene measured on th e Mir prior to and during flowering, plants on earth were exposed to 0, 1, 3, 10, and 20 mu mol . mol(-1) of ethylene gas and 1200 mu mol . mol(-1) CO 2 from 7d after emergence to maturity. As in our Mir wheat, plant height, a wn length, and the flag leaf were significantly shorter in the ethylene-exp osed plants than in controls; inflorescences also exhibited 100% sterility. Scanning-electron-microscopic (SEM) examination of florets from Mir-grown and ethyl ene-treated, earth-grown plants showed that development ceased pr ior to anthesis, and the anthers did not dehisce. Laser scanning confocal m icroscopic (LSCM) examination of pollen grains from Mir and ethyl ene-treat ed plants on earth exhibited zero, one, and occasionally two, but rarely th ree nuclei; pollen produced in the absence of ethylene was always trinuclea te, the normal condition. The scarcity of trinucleate pollen, abrupt cessat ion of floret development prior to anthesis, and excess tillering in wheat plants on Mir and in ethylene-containing atmospheres on earth build a stron g case for the ethylene on Mir as the agent for the induced male sterility and other symptoms, rather than microgravity.