DYNAMICS OF ROOT-GROWTH IN MICROGRAVITY

An experiment to study the growth of garden cress roots in microgravit y is described. The experiment, denoted RANDOM, was an ESA Biorack exp eriment in the IML-2 flight in July 1994. In the absence of gravity, i t can be anticipated that the roots would show random growth, changing their direction randomly. The hypothesis that such random growth move ments occur according to random walk theory, leads to predictions as t o the detailed manner in which deviations increase with time. The expe riment was designed to test this random walk hypothesis. The paper con centrates on the technological aspects of studying the roots in microg ravity. The development of suitable plant chambers, fitting containers developed by ESA, is described as well as the techniques used to grow the seeds between agar slices. Hardware was developed to record photo graphically root movements between the agar slices. Photos were taken once per hour. Some plant chambers were designed to allow fixation of plant material in space. The practical solutions found using glutarald ehyde for prefixation in the Spacelab, within the restrictions given, are described. The experimental results show that the growth pattern i n fact followed the prediction from the random walk approach. The aver age changes in the growth direction stayed constant and equal to zero during the experiment while the squared angular deviations increased p roportional to time. Furthermore, plant material prefixed in orbit was permanently fixed after the flight. Light microscopy and electron mic roscopy pictures are shown as examples of the results achieved. The lo ng prefixation period meant a drawback for the quality of the fixation process. However, sections suitable for study were achieved. The main goals of the RANDOM experiment were therefore achieved.