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Agronomy Journal Abstract -

New Hand-Operated Press for the Extraction of Tissue Sap for the Measurement of Osmotic Potential1


This article in AJ

  1. Vol. 77 No. 1, p. 182-185
    Received: May 21, 1984

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  1. Albert H. Markhart III and
  2. Tsai-Yun Lin2



Conventional methods of extracting sap from leaf tissue for the measurement of osmotic potential are time consuming and often result in changes in sap concentration due to evaporation or enzymatic activity. In this paper, a simple hand operated press is described which facilitates rapid extraction and filtration of tissue contents with either direct deposition on a filter paper disk for osmotic potential measurement or collection in a suitable vial for future analysis. A complete measurement is made in 5 min. Triplicate measurement of samples with the same osmotic potential differed by an average of 0.05 MPa at an osmotic potential of −0.7 MPa. Osmotic potentials measured with a vapor pressure osmometer on expressed sap were 10% higher than values derived from pressure volume carves. This error is most likely due to dilution of the protoplasm by the cell wall water. Convenience and reliability make this new pi-ess a useful tool for the water relations laboratory.

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