EFFECTS OF SPACE FLIGHT (BIOSATELLITE II) AND RADIATION ON FEMALE GAMETOPHYTE DEVELOPMENT IN TRADESCANTIA

Abstract

The mode of female gametophyte development and the cytological effects of orbital flight factors, with and without radiation, on embryo sac development were studied in Tradescantia clone 02 flown in Biosatellite II. One package of 32 rooted inflorescences was exposed during the free‐flight phase of the two‐day orbital flight to about 220 R gamma radiation from an 85Sr source, and a nonirradiated package was flown as a flight control. Two similar packages, one irradiated and one unirradiated, were maintained in a ground‐based vehicle as concurrent nonflight controls. Various postflight ground experiments were conducted in an attempt to associate with specific flight factors the effects observed in the orbited plants. Mature ovaries were fixed daily as the flowers opened for at least 20 days after the treatment, sectioned, stained, and analyzed for the rate of embryo sac abortion and other developmental abnormalities. The embryo sac in Tradescantia clone 02 is eight‐nucleate with a Polygonum type of development. Irradiation during megasporogenesis produced an increased rate of embryo sac abortion and this radiation effect was greater in the environment of the flight vehicle than in the nonflight vehicle. This effect may be due to an increase in concentration of ethylene in the flight vehicle. A synergism between some undetermined flight factor and radiation was found to produce underdeveloped embryo sacs. Malfunctioning of the spindle, most probably due to free flight, was evidenced by the increased number of embryo sacs with misoriented nuclei.