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 promine nt dif fe r e nc e s we r e d e te c te d in the extensibility or the stress-relaxation parameters of the cell wall between spaceg r ow n hy p o c o t yl s a n d g r o u n d c o n t r o l s , 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.

Growth stimulation in inflorescences of an Arabidopsis tubulin mutant under microgravity conditions in space

“…We have expected that growth of stem organs in tubulin mutants may be more or less restored under microgravity conditions, even if cell wall properties are kept constant, because the gravity resistance is not required and the defects of mutants are not disadvantageous for their growth (Hoson et al . ). Although this view was not directly examined in the present study because of cell wall modifications under microgravity conditions, the results as a whole are compatible with the above‐mentioned hypothesis.…”

“…The mechanical properties of the cell wall of each region were measured by a sequential analysis with the stress‐strain and the stress‐relaxation methods with a tensile tester (Tensilon RTM‐25, Toyo Baldwin, Tokyo, Japan) (Hoson et al . ). The middle parts of each region of inflorescences were fixed between two clamps (1 mm apart) and stretched by lowering the bottom clamp at a speed of 10 mm·min −1 until a stress of 1 g was produced.…”

Cortical microtubules are responsible for gravity resistance in plants

“…Unfortunately, no plants developed to the expected developmental stage because of serious anomalies of water supply system. 25 Another space experiment related to this topic, Space Seed, is now underway. We are also preparing for the next experiment named Resist Tubule on the International Space Station.…”

Objectives, Outlines, and Preparation for the Resist Tubule Space Experiment to Understand the Mechanism of Gravity Resistance in Plants

“…Unfortunately, we faced great difficulties in initial watering because of serious anomalies of water supply system in EMCS, probably due to incorrect connections between the life support system and water reservoirs 4) . Thus, no plants developed until the expected developmental stage 5) . In the Resist Tubule experiment, we will challenge again to confirm the above-mentioned hypothesis.…”