Abstract
The water relation in plant is very important to know the dynamics of plant growth, transport and photosynthesis. In the case of water transportation via xylem, especially vessels were ever regarded as passive tissues, only the pathway of water and ion transport. However, recently, it had been reported that they may actively control the mass flow.
In this experiment, we adopted water tracer, [15O]water, and positron detection system, and measured the water flow at an internode between the cotyledon and the first leaf of a 3 week old soybean plant non-invasively and quantitatively. It was shown that a part of the water was leaked out through the vessel at internode, and the leaking speed was estimated to be 20 nl/cm/s. It was enough to compensate the water loss due to the transpiration in the internode. Moreover, it showed that the leaking amount was dependent on the velocity of water flow.
