Journal Article

An Analysis of Long-Distance Water Transport in the Soybean Stem Using H<sub>2</sub><sup>15</sup>O

Tomoyuki Ohya, Keitaro Tanoi, Yousuke Hamada, Hirotaka Okabe, Hiroki Rai, Junko Hojo, Kazutoshi Suzuki and Tomoko M. Nakanishi

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 49, issue 5, pages 718-729
Published in print May 2008 | ISSN: 0032-0781
Published online May 2008 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcn047
An Analysis of Long-Distance Water Transport in the Soybean Stem Using H215O

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The lateral water movement in the intact stem of a transpiring soybean plant was analyzed quantitatively by a real-time measurement system utilizing labeled water, H215O and gamma ray detectors. A large volume of water escaping from xylem vessels during its transport was detected. The escape of water was not influenced by evaporation from the stem surface or mass flow in the sieve tubes. It was assumed that the total amount of water transported through xylem vessels was kept almost completely constant along the internode. As a result, most of the escaped water was found to re-enter the xylem vessels, i.e. water exchange occurred. The analysis of radiographs of tritiated water suggested that the self-diffusion effect of water was strong for lateral water movement, although another driving force besides thermal motion was included in the process, and that the process was also affected by the water permeability of the plasma membrane. An analysis based on a mathematical model showed that the net volume of water which escaped from xylem vessels was not dependent on the transpiration rate of the plant.

Keywords: H215O; Internode; Real-time measurement; Soybean; Water exchange; Water relations

Journal Article.  7965 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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