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The aim of the present study was to test the accuracy of the pressure‐chamber technique as a method for estimating leaf‐cell turgor pressures. To this end, pressure‐probe measurements of cell turgor pressure (P cell ) were made on mesophyll cells of intact, attached leaves of Kalanchoë daigremontiana. Immediately following these measurements, leaves were excised and placed in a pressure chamber for the determination of balance pressure (P bal ). Cell‐sap osmotic pressure (? cell ) and xylem‐sap osmotic pressure (? xyl ) were also measured, and an average cell turgor pressure calculated as P cell =? cell –? xyl –P bal . The apparent value of P bal was positively correlated with the rate of increase of chamber pressure, and there was also a time‐dependent increase associated with water loss. On expressing sap from the xylem, ? xyl fell to a plateau value that was positively correlated with ? cell . Correcting for these effects yielded estimates of P bal and ? xyl at the time of leaf excision. On average, the values of P cell obtained with the two techniques agreed to within ±002 MPa (errors are approximate 95% confidence limits). If ? xyl were ignored, however, the calculated turgor pressures would exceed the measured values by an average of 0.074 ± 0.012MPa, or 48% at the mean measured pressure of 0.155 MPa. We conclude that the pressure‐chamber technique allows a good estimate to be made of turgor pressure in mesophyll cells of K. daigremontiana, provided that ? xyl is included in the determination. The 1:1 relationship between the measured and calculated turgor pressures also implies that the weighted‐average reflection coefficient for the mesophyll cell membranes is close to unity. Copyright © 1994, Wiley Blackwell. All rights reserved

Original publication

DOI

10.1111/j.1365-3040.1994.tb00262.x

Type

Journal article

Journal

Plant, Cell & Environment

Publication Date

01/01/1994

Volume

17

Pages

15 - 29