Lentil root statoliths reach a stable state in microgravity |
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Authors: | Dominique Driss-Ecole Bernard Jeune Monique Prouteau Philippe Julianus Gérald Perbal |
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Institution: | (1) Laboratoire CEMV, Université Pierre et Marie Curie, 4 place Jussieu, Bat. N2, case courrier 150, 75252 Paris Cedex 05, France, FR;(2) Laboratoire d'Ecologie, Université Pierre et Marie Curie, 4 place Jussieu, Bat.C, case courrier 237, 75252 Paris Cedex 05, France, FR |
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Abstract: | The kinetics of the movement of statoliths in gravity-perceiving root cap cells of Lens culinaris L. and the force responsible for it have been analysed under 1 g and under microgravity conditions (S/MM-03 mission of Spacehab 1996). At the beginning of the experiment in space, the amyloplasts
were grouped at the distal pole of the statocytes by a root-tip-directed 1-g centrifugal acceleration. The seedlings were then placed in microgravity for increasing periods of time (13, 29, 46 or 122 min)
and chemically fixed. During the first 29 min of microgravity there were local displacements (mean velocity: 0.154 μm min−1) of some amyloplasts (first at the front of the group and then at the rear). Nevertheless, the group of amyloplasts tended
to reconstitute. After 122 min in microgravity the bulk of amyloplasts had almost reached the proximal pole where further
movement was blocked by the nucleus. After a longer period in microgravity (4 h; experiment carried out 1994 during the IML
2 mission) the statoliths reached a stable position due to the fact that they were stopped by the nucleus. The position was
similar to that observed in roots grown continuously in microgravity. Treatment with cytochalasin D (CD) did not stop the
movement of the amyloplasts but slowed down the velocity of their displacement (0.019 μm min−1). Initial movement patterns were the same as in control roots in water. Comparisons of mean velocities of amyloplast movements
in roots in space and in inverted roots on earth showed that the force responsible for the movement in microgravity (Fc) was about 86% less (Fc = 0.016 pN) than the gravity force (Fg = 0.11 pN). Treatment with CD reduced Fc by two-thirds. The apparent viscosity of the statocyte cytoplasm was found to be 1 Pa s or 3.3 Pa s for control roots or
CD treated roots, respectively. Brownian motion or elastic forces due to endoplasmic reticulum membranes do not cause the
movement of the amyloplasts in microgravity. It is concluded that the force transporting the statoliths is caused by the actomyosin
system.
Received: 22 March 1999 / Accepted: 18 December 1999 |
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Keywords: | : Actin cytoskeleton Lens (statolith movement) Microgravity Statocyte Statolith movement |
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