A non-invasive probe for online-monitoring of turgor pressure changes under field conditions

An advanced non-invasive, field-suitable and inexpensive leaf patch clamp pressure probe for online-monitoring of the water relations of intact leaves is described. The probe measures the attenuated output patch clamp pressure, P-p, of a clamped leaf in response to an externally applied input pressure, P-clamp. P-clamp is generated magnetically. P-p is sensed by a pressure sensor integrated into the magnetic clamp. The magnitude of P-p depends on the transfer function, T-f, of the leaf cells. T-f consists of a turgor pressure-independent (related to the compression of the cuticle, cell walls and other structural elements) and a turgor pressure-dependent term. T-f is dimensionless and assumes values between 0 and 1. Theory shows that T-f is a power function of cell turgor pressure P-c. Concomitant P-p and P-c measurements on grapevines confirmed the relationship between T-f and P-c. P-p peaked if P-c approached zero and assumed low values if P-c reached maximum values. The novel probe was successfully tested on leaves of irrigated and non-irrigated grapevines under field conditions. Data show that slight changes in the microclimate and/or water supply (by irrigation or rain) are reflected very sensitively in P-p.