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Résumé :
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A new in vive 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, (d P/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) = (-d P/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 0.01 MPa) 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)[1 - exp {-k(P P-0)}], where P-0 is a plateau pressure (approximately 0.01 MPa), k is a rate constant (approximately 7 per MPa), and epsilon(infinity) (approximately 10 MPa) is the hypothetical maximum value of epsilon(ave) as P --> infinity. 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.
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