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Use of Unsaturated Salt Solutions to Generate Leaf Tissue Water-Release Curves

Dep. of Soil Science, Univ. of Saskatchewan, Saskatoon, Saskatchewan, Canada, S7N 0W0

^* Corresponding author.

Osmotic adjustment and changes in cell wall elastic modulus are important processes that enable plants to maintain physiological activity and prolong leaf survival as plant water deficits increase. This paper describes a simple and practical technique to produce tissue water-release curves that allows many measurements of osmotic potential (), elastic modulus (), and apoplastic water fraction (A) to be made both rapidly and routinely. Discs, 6 mm in diameter, were punched out of hydrated leaves of wheat (Triticum aestivum L.), barley (Hordeum distichon L.), and oil-seed rape (Brassicu napus and B. campestris) and weighed immediately on a precision balance. Each disc was then suspended above an unsaturated salt solution of known molality in a sealed test tube held at 5°C in a stirred water bath. Eighteen salt solutions were used whose water potentials ranged from –0.09 to –4.67 MPa. After 12 h the discs were reweighed and then oven dried at 65°C for 24 h. Water-release curves were obtained by plotting paired values of disc relative water content and salt solution water potential. Using leaves from the same stem, , at full and zero turgor, , and A determined from the water-release curves were compared with pressure chamber measurements made on the next lower leaf. Measurements of wheat, barley, and oil-seed rape , , and A obtained from water release curves generated using salt solutions were within 0.2 MPa for , 3.0 MPa for , and 0.07 for A, of those obtained using a pressure chamber over a wide range of and . More than 40 water-release curves could be generated over 2 d.

Received for publication September 21, 1987.