MEASUREMENT OF HYPHAL TURGOR

Cellular turgor pressure is thought to provide the driving force for hyphal extension and for a variety of other fungal processes. This study was conducted to evaluate three different approaches to the measurement of hyphal turgor in the aquatic fungus Achlya bisexualis. Turgor was determined indirectly from measurements of the osmotic potential of hyphal extracts using an osmometer and by a refined incipient plasmolysis technique. Turgor was also measured directly from individual growing hyphae using a micropipet-based pressure probe. Osmometry provided an estimate of the mean turgor of hyphae grown in liquid culture of 0.74 MPa, while the incipient plasmolysis technique indicated turgor pressures of between 1.0 and 1.2 MPa (10 to 12 bars). With the pressure probe, turgors ranging from 0.8 to 1.2 MPa were measured from 49 hyphae in the same difined medium. The low turgor estimates from the osmometric approach probably reflected dilution of the cell contents by cell wall and extracellular fluid during sample extraction. Recordings with the pressure probe showed that turgor did not vary along the length of the coenocytic hyphae and was independent of hyphal diameter. This paper presents the first report of the direct measurement of hyphal turgor pressure. © 1990 Academic Press, Inc.