Slow Wave Potentials –a Propagating Electrical Signal Unique to Higher Plants - Communication in Plants: Neuronal Aspects of Plant Life - page 299

Fig. 20.5. After the submersed excision of the lower hypocotyl of an intact sunflower plant
and a waiting period of 60 min that allowed the ascending transpiration stream to return
to its normal rate, the basal end of the shoot was subjected to a 5 mM solution of sodium
azide ( arrow ), an electrogenic model substance known to cause a large depolarization in
plant cells. The transport and release of this substance from the xylem causes a wave of
depolarizations that ascends the stem from the hypocotyl ( lower trace ; the distance to the
basal cut was adjusted to be 10 cm) to the epicotyl ( center trace ; the distance to the basal
cutwas20cm)toaleafblade( upper trace ; the distance to the basal cut was 30 cm). The
transport of this depolarizing chemical produces a signal that differs from a hydraulic SWP
by a much lower propagation speed and the absence of repolarization and transience
floods (Stahlberg et al. 2005a), and perhaps also the reestablishment of pos-
itive xylem pressure during the night in root-pressure-generating plants,
and strong bending of plants under wind and other mechanical influ-
ences.
Foraslongastheyhavebeenrecognizedasdifferententities,SWPs
and APs have been believed to originate from different causes (Sibaoka
1953; Umrath 1959). While the cooling of roots and the application of small
electriccurrentsinthetissueseemtoinduceexclusivelyAPs,theinduc-
tionbyheat(leafflaming)hasbeenreportedtoinduceSWPsaswellasAPs
(Roblin 1985; Wildon et al. 1992; Stankovic et al. 1997, 1998). Repeated flam-
ing of sunflower leaves changed the shape of the resulting stem response
from a clear SWP to an AP-like signal (Davies et al. 1991). These data in-
dicate the possibility of an interaction between SWPs and APs that has not
been investigated. Both APs and SWPs are propagated within the vascular