THE BEHAVIOR OF NORMAL AND AGRAVITROPIC TRANSGENIC ROOTS OF RAPESEED (BRASSICA-NAPUS L) UNDER MICROGRAVITY CONDITIONS

In the TRANSFORM experiment for IML-2 on the Space Shuttle Columbia, n ormal (wild type = WT) and genetically transformed agravitropic rapese ed roots were tested under microgravity conditions. The aim of the exp eriment was to determine if the wild-type roots behaved differently (g rowth, morphology, gravitropical sensitivity) from the transgenic root s. The appearance of the organelles and distribution of statoliths (i. e. amyloplasts with starch grains) in the gravitropic reactive cells ( statocytes) under weightlessness was compared for the two types of roo ts. Attempts have also been made to regenerate new plants from the roo t material tested in space. Both the WT and the transgenic root types showed the expected increase in length during 36 h of photorecording. Contrary to the results of the ground controls, no significant differe nce in elongation rates was found between the WT and transgenic roots grown in orbit. However, there are indications that the total growth b oth in the WT and the transgenic roots was higher in the ground contro l than for roots in orbit. After a 60 min 1 x g stimulation of the roo ts on board the Shuttle, no detectable curvatures were obtained in eit her the transgenic or the WT roots. However, it cannot be excluded tha t a minute curvature development occurs in the root tips but was not d etected due to technical reasons. The ultrastructure was well preserve d in both the WT and the transgenic roots, despite the fact that the t issue was kept in the prefixative for over 3 weeks. No marked differen ces in ultrastructure were observed between the transformed root stato cyte cells and the equivalent cells in the wild type. There were no ob vious differences in root morphology during the orbital period. Light micrographs and morphometrical analysis indicate that the amyloplasts of both the wild type and transformed root statocytes are randomly dis tributed over the cells kept under micro-g conditions for 37 h after a 14 h stimulation on the 1 x g centrifuge. The main scientific conclus ion from the TRANSFORM experiment is that the difference in growth fou nd in the ground control between the WT and the transgenic root types seems to be eliminated under weightlessness. Explanations for this beh aviour cannot be found in the root ultrastructure or in root morpholog y.