Plant growth and development are affected by abiotic factors such as light, temperature, water and gravity. Gravity ensures primary shoot grows upward towards sunlight to optimize photosynthesis, while the primary root grows downward into the soil to find water and mineral supply. Plants with impaired gravity response are poorly fit for survival in nature, since the roots may not be able to absorb the nutrient and the shoot may not be able to track sunlight. In the first study, the tomato seedlings on agar medium were treated on clinostat in light and dark condition. In dark, the tomato seedlings on the clinostat responded by bending their shoot and coiled their root. In the light condition, the shoot bending and root coiling were reduced significantly compare to the plants grew in the dark after seven days in clinorotation, which might indicate that phototropic response was stronger than gravitropic response in tomato seedlings. The mung bean on hanging mesh was tested on clinostat without light. Under this condition, instead of coiling, the root grew staight to the wet rockwool. The condition might indicate that mung bean seedling has stronger hidrotropic response compare to gravitropic response, as moisture gradient may trigger statolith degradation in columella cells.
2014 The Japan Society for Aeronautical and Space Sciences