Changes in the rheological properties of the cell wall of plant seedlings under simulated microgravity conditions.

In this review article, we discuss the changes in the mechanical properties of the primary cell wall of different organs of several species of plant seedlings grown under simulated microgravity conditions. We compared growth and tropistic responses of these organs growing under different microgravity conditions, namely: 1) 3-D clinostat (three-dimensional clinostat with two axes); 2) water-submergence for rice seedlings, and 3) for comparison, an accelerated gravity using a specifically designed centrifuge. We measured the minimum stress-relaxation time as the parameter representing the mechanical property of the cell wall. We also measured extensiblity, in mm/g. The 3-D clinostat condition disturbed the normal gravitropic response of organs but affected growth rate and mechanical properties of the cell wall very little. Water-submergence of rice seedlings caused an acceleration of coleoptile elongation in the dark and caused a marked change in the mechanical property of the cell wall. However, the additional gravity of 30-135 xg showed only a small effect on growth and the mechanical property of the cell wall.