|Budget Amount *help
¥2,200,000 (Direct Cost : ¥2,200,000)
Fiscal Year 1996 : ¥400,000 (Direct Cost : ¥400,000)
Fiscal Year 1995 : ¥1,800,000 (Direct Cost : ¥1,800,000)
To develop water/nutrient delivery system for plant growth facility and method to control root growth in space, we studied the mechanism for hydrotropic response in roots and fundamental aspects of its application to plant cultivation in space.
Under a simulated condition of plant growth in space by using agravitropic pea mutant, ageotropum, we determined the threshold time required for the perception of moisture gradient and time required for the movement of hydrotropic signal from the perception site, the root cap, to the responsive site, the elongation region, in inducing positive hydrotropism. Perception of hydrotropic stimulus by the root cap occurred within 2 minutes, but it took longer than 90 minutes for the hydrotropic signal to move from the cap to the elongation region. Furthermore, it was found that apoplastic free calcium in the root cap and its influx through a certain type of calcium channel play important role in inducing hydrotropic response of roots. It was also sugges
ted that distal elongation zone of roots of agravitropic pea mutant, ageotropum, was insensitive to a gradient of apoplastic calcium level, which might account for agravitropic growth of the roots. Nevertheless, roots of ageotropum roots strongly responded to a moisture gradient by inducing hydrotropism. These results suggest that there exist some differences in signal transduction mechanisms between hydrotropism and gravitropism in roots. Differential growth of hydrotropically responding roots was found to occur due to a differential change in cell wall extensibility between the dry side and the moistened side of the roots. We isolated an endo-xyloglucan transferase (EXGT) gene (from ageotropum pea roots) considered to play a key role in cell wall loosening and cell elongation, and showed that expression of EXGT gene was responsible for the induction of hydrotropism. Root hydrotropism that occurs due to the signal transduction mechanism different from that of gravitropism, may be useful for controlling root growth under microgravity conditions in space. Less