XVI International Botanical Congess

We have used the pulvini of Maize and oats to investigate the involvement of phosphoinositides in gravitropism. A rapid, transient increase in inositol- 1,4,5-trisphosphate (IP3) was detected in both systems within 15 s of gravistimulation. In maize, the increase in IP3 was detected initially in the lower half of the pulvinus followed by a fluctuation of the IP3 levels in the upper and lower half for about 1 h compared to vertical controls. After 2 h of gravistimulation, the lower half had significantly higher IP3 that continued to increase to 5-fold above the control value and then decreased prior to visible growth. A similar sustained increase in IP3 was observed in the lower half of the oat pulvini only the time scale was shorter. Both short-term and long-term changes in IP3 during graviperception and response would enable the plant to distinguish between transient movements caused by the wind and permanent lodging.