Journal Article

The transmission of gas pressure to xylem fluid pressure when plants are inside a pressure bomb

C. Wei, M.T. Tyree and J.P. Bennink

in Journal of Experimental Botany

Published on behalf of Society for Experimental Biology

Volume 51, issue 343, pages 309-316
Published in print February 2000 | ISSN: 0022-0957
Published online February 2000 | e-ISSN: 1460-2431 | DOI: http://dx.doi.org/10.1093/jexbot/51.343.309
The transmission of gas pressure to xylem fluid pressure when plants are inside a pressure bomb

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In earlier work tobacco leaves were placed in a Scholander–Hammel pressure bomb and the end of the petiole sealed with a pressure transducer in order to measure pressure transmission from the compressed gas (Pg) in the bomb to the xylem fluid (Px). Pressure bomb theory would predict a 1 : 1 relationship for Pg:Px when tobacco leaves start at a balance pressure of zero. Failure to observe the expected 1 : 1 relationship has cast doubt on the pressure‐bomb technique in the measurement of the xylem pressure of plants.

The experimental and theoretical relationship between Px and Pg was investigated in Tsuga canadensis (L) branches and Nicotiana rustica (L) leaves in this paper. It is concluded that the non 1 : 1 outcome was due to the compression of air bubbles in embolized xylem vessels, evaporation of water from the tissue, and the expansion of the sealed stem segment (or petiole) protruding beyond the seal of the pressure bomb. The expected 1 : 1 relationship could be obtained when xylem embolism was eliminated and stem expansion prevented. It is argued that the non 1 : 1 relationship in the positive pressure range does not invalidate the Scholander pressure bomb method of measuring xylem pressure in plants because Px never reaches positive values during the determination of the balance pressure.

Keywords: Pressure bomb; embolism; Tsuga canadensis; Nicotiana rustica

Journal Article.  5775 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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