References

286 K.Trebacz,H.Dziubinska,E.Krol
nmolCO (g ) min
-1 -1
2 DW
mV
800
700
600
500
50
25
0
a
respiration rate
potential difference
5 min
b
Fig.19.4. Respiration rate (upper traces) andAPs(lower traces) inC. conicum. a Response
to a single electrical stimulus; b response to cutting a thallus edge (After Dziubinska et al.
1989)
evoked a burst of respiration provided an AP had been generated. In the
thalli preincubated with TEA, in which excitability was blocked, no significant
change in the respiration rate occurred in spite of wounding. In
untreatedplantswhencuttingreleasedaseriesofAPs,eachAPinthesequence
was followed by enhancement of respiration (Fig. 19.4). Changes
in respiration rate concomitant with AP generation were registered among
others in Cucurbita pepo and Vicia faba (Gunar and Sinyukhin 1963; Filek
and Koscielniak 1997). There are also reports on changes in the level of photosynthesis
evoked by stimuli able to evoke APs (Fromm and Eschrich 1993;
Koziolek et al. 2003). The list of remaining physiological consequences of
plant excitation covers, among others, temporary lowering of the growth
rate in Luffa cylindrica (Shiina and Tazawa 1986) and Helianthus annuus
(Stankovic et al. 1998), a decrease in susceptibility to cold stress in Cucurbita
pepo (Retivin et al. 1997), enhancement of peroxidase activity in
Conocephalum conicum (Dziubinska et al. 1999) and induction of jasmonic
acid biosynthesis in Solanum tuberosum (Fisahn et al. 2004).
APs are also found to play a role in gene expression. Special attention
was paid to regulation of the PINII gene whose products play a key role
in a systemic response to wounding (Wildon et al. 1992). There was controversy
as to the nature of the electrical signal preceding the response.
Stankovic and Davies (1996) demonstrated that both APs and VPs induce
PINII gene expression.
A frequently asked question is: how can such a uniform signal as an AP
evoke such different responses or, more precisely, how can ion fluxes and