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Development and Growth Regulation

Pressure Probe and Isopiestic Psychrometer Measure Similar Turgor ¹

Department of Plant Biology, University of Illinois, Urbana, Illinois 61801, Department of Agronomy, University of Illinois, Urbana, Illinois 61801, United States Department of Agriculture, Agricultural Research Service, University of Illinois, Urbana, Illinois 61801

Turgor measured with a miniature pressure probe was compared to that measured with an isopiestic thermocouple psychrometer in mature regions of soybean (Glycine max [L.] Merr.) stems. The probe measured turgor directly in cells of intact stems whereas the psychrometer measured the water potential and osmotic potential of excised stem segments and turgor was calculated by difference. When care was taken to prevent dehydration when working with the pressure probe, and diffusive resistance and dilution errors with the psychrometer, both methods gave similar values of turgor whether the plants were dehydrating or rehydrating. This finding, together with the previously demonstrated similarity in turgor measured with the isopiestic psychrometer and a pressure chamber, indicates that the pressure probe provides accurate measurements of turgor despite the need to penetrate the cell. On the other hand, it suggests that as long as precautions are taken to obtain accurate values for the water potential and osmotic potential, turgor can be determined by isopiestic psychrometry in tissues not accessible to the pressure probe for physical reasons.

³ This work was done while E. S. was on leave from the Institut für Radioagronomie of the Kernforschungsanlage Jülich, Postfach 1913, D-5170 Jülich, Federal Republic of Germany.

¹ Supported by National Science Foundation grant PCM79-09790 and Department of Energy grant DE-FG05-84ER 13273 to J. S. B. and by a grant from the Deutsche Forschungsgemeinschraft (Ste 319/1-2) to E. S.

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