Growth and Cell Wall Properties in Hypocotyls of Arabidopsis tua6 Mutant under Microgravity Conditions in Space

Abstract

Seedlings of Arabidopsis α-tubulin 6 mutant (tua6) were cultivated under microgravity conditions in the European Modular Cultivation System on the International Space Station, and growth and cell wall properties of their hypocotyls were analyzed (the Resist Wall experiment). Seeds of tua6 mutant were shown to germinate and grow normally until the seedling stage under microgravity conditions, as at 1 G on the ground. The seedlings were naturally air-dried in orbit, which were then recovered and transported to earth. When the mechanical properties of the cell wall of rehydrated hypocotyls were examined with a tensile tester, the hypocotyls showed typical stress-strain and stress-relaxation curves, as normally fixed or frozen materials. Also, no prominent differences were detected in the extensibility or the stress-relaxation parameters of the cell wall between space-grown hypocotyls and ground controls, suggesting that tua6 hypocotyls formed the regular cell wall architecture under microgravity conditions. The results and lessons learned from the Resist Wall experiment are expected to provide the basis for the following space experiments to clarify the mechanism of gravity resistance in plants.