HYDROTROPISM AND AUXIN-INDUCIBLE GENE EXPRESSION IN ROOTS GROWN UNDER
MICROGRAVITY CONDITIONS (HYDRO TROPI)
Research Area: Plant Biology
Expedition(s): 25
Principle Investigator(s): ● Hideyuki Takahashi, PhD, Tohoku University, Sendai, Japan
RESEARCH OBJECTIVES
Hydrotropism and Auxin-Inducible Gene Expression in Roots Grown under Microgravity
Conditions (Hydro Tropi) uses the microgravity environment of space to separate hydrotropism
from gravitropism and to dissect its mechanism in cucumber roots. This experiment aims to
demonstrate that gravitropism interferes with hydrotropism. Second, it clarifies the differential
auxin response that occurs during the respective tropisms by investigating the auxin-inducible
gene expression. Lastly, it shows whether hydrotropism can be used in controlling root growth
orientation in microgravity.
EARTH BENEFITS
Water availability is a critical matter for plant growth and survival. For example, crop cultivation
and yields are indeed restricted under drought conditions in an arid area. The results of Hydro
Tropi provides additional knowledge to develop new technology that enables plants to
efficiently uptake water.
SPACE BENEFITS
Hydro Tropi demonstrates a plants ability to respond to moisture gradients. It also aims to
provide basic information for creating new plants suitable for the hydrotropism-assisted plant
growth unit or developing a hydrotropism-controlled growth unit itself for future space
exploration.
RESULTS
The on-board experiments were successfully
carried out and researchers measured the
growth and curvature of the seedling roots
and analyzed CsIAA1 expression by in situ
hybridization. The results showed that roots
hydrotropically bent toward the moistened
plastic foam under microgravity conditions,
whereas they grew straight along the
direction of gravitational force under 1G
conditions. The hydrotropic response in
microgravity appeared to be greater in the
NaCl chamber compared with that in H 2 O
chamber, but they did not differ statistically.
Furthermore, CsIAA1 gene differentially expressed in the hydrotropically bending roots; the
expression was much greater on the concave side than on the convex side. On the other hand,
ISS025E0077880 - Astronaut, Shannon Walker, is
working on the Hydro Tropi experiment in Kibo module.
JAXA image.