Th. Iversen et al., THE BEHAVIOR OF NORMAL AND AGRAVITROPIC TRANSGENIC ROOTS OF RAPESEED (BRASSICA-NAPUS L) UNDER MICROGRAVITY CONDITIONS, Journal of biotechnology, 47(2-3), 1996, pp. 137-154
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.