Electric Signals Released from Roots of Willow (Salix viminalis L.) Change Transpiration and Photosynthesis

Summary Using willow plants ( Salix viminalis L.) raised from cuttings, electric excitability and signal transmission were investigated extra- and intracellularly. Following root stimulation, willow plants generate action potentials that are propagated throughout the plant at velocities of 2 to 5 cm sec −1 . Shifts in CO 2 , O 2 and H 2 O exchange indicate the arrival of a signal in the leaves. The hydroponically grown root system is stimulated by providing nutrients, hormones or pH-changes. While the application of nutrients, auxin and cytokinins commonly leads to an increase in both CO 2 -uptake rate and transpiration rate, abscisic acid and acidification from pH 7.0 to pH 4.0 cause a decrease in both CO 2 -uptake rate and transpiration rate. Following all applications the foliar gas exchange responded constantly after 3 min. It is calculated that this lag is too short for moving a signalling substance to the leaves via the transpiration stream. This indicates that rapidly evoked and propagated electric signals are the route whereby stimulations are transmitted.