Measurement of a growth-induced water potential gradient in tall fescue leaves

Spatial distribution of cell turgor pressure, cell osmotic pressure and relative elemental growth rate were measured in growing tall fescue leaves (Festuca arundinacea). Cell turgor pressure (measured with a pressure probe) was c. 0.55 MPa in expanding cells but increased steeply (+ 0.3 MPa) in cells where elongation had stopped. However, cell osmotic pressure (measured with a picolitre osmometer) was almost constant at 0.85 MPa throughout the leaf. The water potential difference between the growth zone and the mature zone (0.3 MPa) was interpreted as a growth-induced water potential gradient. This and further implications for the mechanism of growth control are discussed.