Slow Wave Potentials –a Propagating Electrical Signal Unique to Higher Plants - Communication in Plants: Neuronal Aspects of Plant Life - page 304

(Stahlberg et al. 2005b). Leaf effects range from shutdown of stomata
(Wildon et al. 1993; Pena-Cortes et al. 1995), to shutdown of photosyn-
thesis (Koziolek et al. 2003), increased production of jasmonic acid and
up-regulated transcription of proteinase inhibitor II and calmodulin in
tomato plants (Herde et al. 1996; Stankovic and Davies 1998). Less is known
aboutrootresponsestoSWPs.Sunflowerandcucumberplantsdeveloproot
pressure that is metabolically supported and sensitive to pressure signals
that can eliminate it in a rapid and drastic all-or-nothing manner (Stahlberg
and Cosgrove 1997b). Leaf flaming generates basipetal electrical and pres-
sure signals that could switch the root pump off and could cause in this
way the observed flame-induced shrinking of sunflower stems (Stankovic
et al. 1997). This has not been tested yet. Although there is almost no in-
formationonSWPsinroots,earlyworkin Vicia indicates that the protein
metabolism in roots is as sensitive to hydraulic signals as in shoots (Theilet
et al. 1982).
20.7
WPs and SWPs
Although both APs and SWPs have been called wound signals, there is
an electrical signal more deserving of this name. WPs occur not only in
higher plants, but also in excised plant organs, nonvascular plants and algae
(Shimmen 2001). A tandem pair of Chara internodal cells is a simple sys-
tem to study cellular interactions. When one cell is damaged or killed, the
neighboring cell undergoes a WP in the form of a large transient depolar-
ization, sometimes with and sometimes without the occurrence of spikes
(Shimmen 2001). Although cellular networks are more complex, cucumber
hypocotyls showed identical responses (Stahlberg and Cosgrove 1994). WPs
in cucumber hypocotyls extend for a distance of 40 mm (a length corre-
sponding to about 200 epidermal cells), 10 mm in pea epicotyls (Stahlberg
and Cosgrove 1994), 5 mm in corn roots (Chastain and Hanson 1982),
and 1 mm in barley roots (Mertz and Higinbotham 1976). WPs appear as
universal signals with specific extensions for different species and organs.
Touch causes a similar response; a slowly repolarizing local depolarization
with amplitudes that depend on the strength of the mechanical stimulus
(Okamoto 1955; Zerrenthin and Stahlberg 1982).
Evidence exists from Chara tandem cells, sugar beet roots and cucumber
hypocotyls that the size of the turgor pressure of the victim cell(s) before
injury affects the amplitude of the generated WPs (Kinraide and Wyse
1986; Shimmen 2001; Stahlberg and Cosgrove 1997a). WPs in higher plants
seem to be caused by a rapid inhibition of P-type H + pumps in the effected
cells (Chastain and Hanson 1982; Gronewald and Hanson 1980; Kinraide