Growth and development, and auxin polar transport in higher plants under microgravity conditions in space: BRIC-AUX on STS-95 space experiment

The principal objectives of the space experiment, BRIC-AUX on STS-95, were the integrated analysis of the growth and development of etiolated pea and maize seedlings in space and a study of the effects of microgravity conditi ons in space on auxin polar transport in these segments. Microgravity signi ficantly affected the growth and develop ment of etiolated pea and maize se edlings. Epicotyls of etiolated pea seedlings were the most oriented toward about 40 to 60 degrees from the vertical. Mesocotyls of etiolated maize se edlings were curved at random during space flight but coleoptiles were almo st straight. Finally the growth inhibition of these seedlings in space was also observed. Roots of some pea seedlings grew toward to the aerial space of Plant Growth Chamber. Extensibilities of cell walls of the third interno de of etiolated pea epicotyls and the top region of etiolated maize coleopt iles, which were germinated and grown under microgravity conditions in spac e, were significantly low as compared with those grown on the ground of the :earth. Activities of auxin polar transport in the second internode segment s of etiolated pea seedlings and coleoptile segments of etiolated maize see dlings were significantly inhibited and promoted, respectively, under micro gravity conditions in space. These results strongly suggest that auxin pola r transport as well as the growth and develop ment of plants is controlled under gravity on the earth.