Transpiration Responses to Potential Volatile Signals and Hydraulic Failure in Single Leaves of Vitis vinifera (cv. Shiraz) and Arabidopsis thaliana (Col 0) Utilising Sensitive Liquid Flow and Simultaneous Gas Exchange.

Volatile organic compounds (VOCs) may communicate stress between plants. However little appears to be documented on how such VOCs affect transpiration. Changes in transpiration in response to some VOCs was examined by measurement of flow (Q) at high resolution into detached leaves of Vitis vinifera (cv. Shiraz) and Arabidopsis (Col 0). Sensors recorded arrival and decay of volatiles at the leaf lamina. Moderate xylem tensions were developed in V. vinifera leaves by incorporating a hydraulic resistance in the flow pathway. Simultaneous recording of leaf gas exchange (Assimilation, A, and Transpiration, E) for both V. vinifera and Arabidopsis revealed that for Arabidopsis Q was stochastically restricted by the gas exchange cuvette but not E in the short term. Depending on the applied supply pressure cavitation could be controlled in V. vinifera evident from reduced Q, and leaf wilting. Stomatal closure occurred upon cavitation after a transitory increase in E and A, and after wilting began and was reversed by re-pressurization. VOCs were emitted from leaves corresponding to changes in flow rate, and light to dark transitions but not to cavitation. Volatile methanol but not ethanol or methyl salicylate induced a localised dose-dependent reversible stomatal closure in both V. vinifera and Arabidopsis.