Hydraulic properties of living late metaxylem and interactions between transpiration and xylem pressure in maize |
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Authors: | Meuser J; Frensch J |
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Institution: | Lehrstuhl fur Pflanzenokologie, Univeritat Bayreuth, D-95440 Bayreuth, Germany; Corresponding author e-mail: jurgen.frensch@uni-bayreuth.de |
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Abstract: | A new approach to study dynamic interactions between transpiration and
xylem pressure in intact plants is presented. Pressure probe measurements
were preformed in living (immature) late metaxylem of maize roots rather
than in adjacent mature xylem. This eliminated technical limitations
related to the measurement of negative pressures. Water relations of single
cells showed that turgor and volumetric elastic modulus were significantly
larger in living metaxylem than in cortical cells; hydraulic conductivity
was similar in both types of root cells. Increasing transpiration induced
an immediate decrease of xylem pressure, and vice versa. Turgor in the
living metaxylem could be continuously recorded for more than 1 h. The
relationship between xylem pressure and transpiration yielded a root
hydraulic resistance of 1.3 x 109 MPa s
m-3. Control experiments indicated that the response
of living xylem in the positive pressure range essentially paralleled that
of mature root xylem in the negative range. In mature xylem, pressures as
low as -0.55 MPa were recorded for short periods (several minutes). Several
tests verified that the pressure probe was in contact with mature xylem
during the measurements of tensions. The results demonstrate convincingly
that transpiration generates an effective driving force for water uptake in
roots, a central feature of the cohesion theory.Key
words: Hydraulic conductivity, negative pressure, root
development, turgor, water transport, Zea mays.
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