PLANT PHYSIOLOGY , Vol 107, Issue 3 995-1005, Copyright © 1995 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
A New Pressure Probe Method to Determine the Average Volumetric Elastic Modulus of Cells in Plant Tissue
R. Murphy and JKE. Ortega
Department of Mechanical Engineering, Bioengineering Laboratory, University of Colorado at Denver, Campus Box 112, P.O. Box 173364, Denver, Colorado 80217-3364
A new in vivo method was used to determine an average volumetric elastic
modulus ([epsilon]ave) for nongrowing cells in plant tissue. This method
requires that both the relative transpiration rate, T, of the tissue and
the average turgor pressure decay rate, (dP/dt)ave, of the cells are
measured after the water source is removed from the plant tissue. Then
[epsilon]ave is calculated from the equation [epsilon]ave = (-dP/dt)ave/T.
This method was used to determine [epsilon]ave for cortical cells in stems
of pea seedlings (Pisum sativum L.). The results demonstrate that
[epsilon]ave increases from virtually zero at low P (approximately 0.01MPa)
to approximately 10 MPa at high P (approximately 0.5 MPa). Analyses of the
results indicate that the relationship between [epsilon]ave and P can be
approximated by a linear function and more accurately approximated by a
saturating exponential function: [epsilon]ave = [epsilon][infinity
symbol][1 - exp {-k(P - Po)}], where Po is a plateau pressure
(approximately 0.01 MPa), k is a rate constant (approximately 7 per MPa),
and [epsilon][infinity symbol] (approximately 10 MPa) is the hypothetical
maximum value of [epsilon]ave as P -> [infinity symbol]. Solutions for
the turgor pressure decay (due to transpiration) as functions of time and
symplasmic water mass (after the water source is removed) are derived.
