Microgravity enhances the phenotype of Arabidopsis zigzag-1 and reduces the Wortmannin-induced vacuole fusion in root cells

The spaceflight environment of the International Space Station poses a multitude of stresses on plant growth including reduced gravity. Plants exposed to microgravity and other conditions on the ISS display root skewing, changes in gene expression and protein abundance that may result in changes in cell wall composition, antioxidant accumulation and modification of growth anisotropy. Systematic studies that address the effects of microgravity on cellular organelles are lacking but altered numbers and sizes of vacuoles have been detected in previous flights. The prominent size of plant vacuoles makes them ideal models to study organelle dynamics in space. Here, we used Arabidopsis zigzag-1 (zig-1) as a sensitized genotype to study the effect of microgravity on plant vacuole fusion. Wortmannin was used to induce vacuole fusion in seedlings and a formaldehyde-based fixation protocol was developed to visualize plant vacuole morphology after sample return, using confocal microscopy. Our results indicate that microgravity enhances the zig-1 phenotype by reducing hypocotyl growth and vacuole fusion in some cells. This study demonstrates the feasibility of chemical inhibitor treatments for plant cell biology experiments in space.