Leaf patch clamp pressure probe measurements on olive leaves in a nearly turgorless state

Abstract

The non-invasive leaf patch clamp pressure (LPCP) probe measures the attenuated pressure of a leaf patch, P(p) , in response to an externally applied magnetic force. P(p) is inversely coupled with leaf turgor pressure, P(c) , i.e. at high P(c) values the P(p) values are small and at low P(c) values the P(p) values are high. This relationship between P(c) and P(p) could also be verified for 2-m tall olive trees under laboratory conditions using the cell turgor pressure probe. When the laboratory plants were subjected to severe water stress (P(c) dropped below ca. 50 kPa), P(p) curves show reverse diurnal changes, i.e. during the light regime (high transpiration) a minimum P(p) value, and during darkness a peak P(p) value is recorded. This reversal of the P(p) curves was completely reversible. Upon watering, the original diurnal P(p) changes were re-established within 2-3 days. Olive trees in the field showed a similar turnover of the shape of the P(p) curves upon drought, despite pronounced fluctuations in microclimate. The reversal of the P(p) curves is most likely due to accumulation of air in the leaves. This assumption was supported with cross-sections through leaves subjected to prolonged drought. In contrast to well-watered leaves, microscopic inspection of leaves exhibiting inverse diurnal P(p) curves revealed large air-filled areas in parenchyma tissue. Significantly larger amounts of air could also be extracted from water-stressed leaves than from well-watered leaves using the cell turgor pressure probe. Furthermore, theoretical analysis of the experimental P(p) curves shows that the propagation of pressure through the nearly turgorless leaf must be exclusively dictated by air. Equations are derived that provide valuable information about the water status of olive leaves close to zero P(c) .

Plant-Based Methods for Irrigation Scheduling of Woody Crops

“…Above a certain level of dehydration, air and vapour accumulates in the leaf tissues and the pressure chip does not properly sense the turgor pressure. The extent to which this limitation curtails the potential of the ZIM probes to monitor water stress was assessed for olive by Fernández et al [49] and Ehrenberger et al [164]. Other effects of the environmental conditions and plant hydraulic functioning on the performance of the ZIM probe, were detailed by Zimmermann et al [163].…”

A non-invasive plant-based probe for continuous monitoring of water stress in real time: a new tool for irrigation scheduling and deeper insight into drought and salinity stress physiology

“…P p assumes minimum values during the day and maximum values during the night ( Figure 7B). The reason for this is most likely a very unfavourable water to air ratio within the leaves (for details, see Ehrenberger et al 2012). At turgor pressure values close to zero the compression of the large air-filled spaces mostly determines the response of the probe; the attenuation factor F a in Eq.…”

Advanced techniques using the plant as indicator of irrigation management

“…These indicators, according to the authors, are useful for the analysis of plant water status. EHRENBERGER et al (2012) studied water relations in oak trees, analyzing its dependence on microclimate and soil moisture. These authors used dendrometers and the sensor, among other equipment, to measure variations in leaf turgor pressure.…”