Water exchange phenomenon in xylem tissue for a soybean plant

Abstract

We developed real-time measuring system for [¹⁵O]water, which is a positron emitter with an extremely short half-life, 2 minutes. Using a pair of BGO (Bi₄Ge₃O₁₂) which was set as close as possible to a stem of a soybean plant, it was possible to measure a trace amount of water, μl level, within the 1cm length of the stem. Through this system, water in xylem vessels was found to exchange with the water outside of the vessels. To analyze water exchange manner more in detail, water evaporation rate as well as water translocation rate was measured under different humidity condition. The water exchange rate was kept the same when humidity was changed from 55% to 80%, when water evaporation amount was drastically reduced. The water leaking site of the xylem vessels was now under investigation using ³H-labeled water with imaging plate.