2001 Volume 50 Issue 5 Pages 163-168
We present a circadian rhythm of water uptake manner in a soybean plant through realtime imaging of water, labeled with 15O. Nitrogen gas was irradiated with deuterons accelerated by a cyclotron at Hamamatsu Photonics Co. to produce 15O-labeled water. Then the 15O-labeled water was supplied to a soybean plant from the root and the realtime water uptake amount was measured for 20 min by Positron Emitting Tracer Imaging System (PETIS) . All the targeting positions for the measurements were stems, two points at an internode between root and the first leaves, between the first leaves and the first trifoliates and between the first trifoliates and the second trifoliates. The water uptake amount was gradually increased and showed its maximum at around 13: 00, especially at the basal part of the stem. Then the water uptake activity was gradually decreased until 17: 00. The water amount taken up by a plant at 13: 00 was about 40% higher than that at 17: 00.