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Determination of the Volumetric Modulus of Elasticity of Wheat Leaves by Pressure-Volume Relations and the Effect of Drought Conditioning¹

A pressure-volume (P-V) method was modified to facilitate the rapid determination of more points in the positive turgor region of P-V dehydration curves of vernalized winter wheat (Triticum aestivum L. cv. Yorkstar) leaves. This allowed for a more accurate estimate of the volumetric modulus of elasticity () and its dependence on turgor. P-V relations during dehydration in a pressure bomb were characterized for leaves from either well-watered plants (control,-solute potential, _s = –1.0 MPa) or plants previously subjected to two stress cycles (conditioned, _s = –1.4 MPa). Prior to P-V determinations, the plants were brought to maximumh ydration by thorough watering and maintenance in the dark for 12 hours (water potential = –0.02 MPa and –0.07 MPa for control and conditioned leaves, respectively). Additionally, P-V relations of leaves from conditioned plants subjected to a third stress (_s = –1.9 MPa) were determined. In this case, leaves were rapidly rehydrated in the pressure bomb prior to the P-V measurements. For leaves of both control and conditioned plants, was constant and nonohysteretic over a range of applied pressure of 0.0 to 0.8 MPa, i.e., at high values of turgor. The turgor dependence of at higher applied pressures (i.e., lower turgor pressures) was not considered because of the unresolvable influence of variations in _s of individual cells in the leaf. Leaves of conditioned plants had a significantly higher (28 MPa) than leaves of control plants (22 MPa). The value of of leaves of plants subjected to three stress cycles and rapidly rehydrated in the pressure bomb before determination of the P-V relations increased to 40 MPa—significantly different from plants subjected to two stress cycles and slow rehydration.

Key Words: Triticum aestivum L. • Pressure bomb • Turgor potential • Solute potential • Capillary system

² Graduate research assistant, research associate, and professor, respectively, Dep. of Agronomy, Cornell Univ., Ithaca, N.Y. 14853.

Received for publication March 24, 1981.

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