MEASUREMENT OF GRADIENTS OF WATER POTENTIAL IN ELONGATING PEA STEM BY PRESSURE PROBE AND PICOLITRE OSMOMETRY

The magnitude of gradients of water potential in growing tissues will reflect processes which limit growth rate and can thus provide information on the mechanism of control of growth in those tissues. A new picolitre osmometry technique was used, together with a sampling pressure probe, to measure gradients of water potential between growing and non-growing regions of pea stems. Such gradients were found to be small and it was therefore concluded that hydraulic conductivity within the expanding region is unlikely to be important in limitation of growth. This and further implications for the mechanism of growth control in this tissue are discussed.