Agriculture Reference
In-Depth Information
20.1
A New Effort to Decipher the Impact
of Electrical Long-Distance Signals in Plants
For a long time plants were thought to be organisms whose limited ability to
move and respond was matched by limited abilities of sensing. Exceptions
were plants with rapid, purposeful movements such as Mimosa pudica ,
Droseras (sundews) ,Dioneamuscipula (flytraps) and tendrils of climbing
plants. These “sensitive plants” attracted the attention of researchers like
Pfeffer, Burdon-Sanderson (1873), Darwin, and Haberlandt (1890; 1914).
They found that these plants use sensitive mechanoreceptors and action
potentials (APs) that implemented these movements. Although hardly ap-
preciated at that time, the discovery that normal plants such as pumpkins
had propagating APs just as the sensitive plants (Gunar and Sinykhin 1962,
1963) was an important scientific landmark. First, it corrected the long-held
belief that normal plants are less responsive than sensitive plants. Second,
it led to a new, eagerly pursued belief that such widely distributed electric
signalsmustcarrymessageswithanimportancethatcouldexceedthein-
duction of organ movements in animals and sensitive plants. In different
laboratories around the world this anticipation became the driving force
for a renewed quest to decipher the meaning of electrical plant signals.
Considerable progress was made in linking electrical signals with respira-
tion and photosynthesis (Gunar and Sinykhin 1963; Koziolek et al. 2003),
pollination (Sinykhin and Britikov 1967; Spanjers 1981), phloem transport
(Opritov 1978; Fromm and Bauer 1994), rapid deployment of plant defenses
(Wildon et al. 1992; Malone et al. 1994; Alarcon and Malone 1995; Herde et
al. 1995, 1996; Stankovic and Davies 1996, 1998).
However, with only a few scattered laboratories producing results, new
data suffered an almost constant lack of confirmation by other laboratories.
This slow progress is traceable in the case of the plant-wide or systemic
induction of proteinase inhibitors in wounded tomato plants, which was
discovered as early as 1972 (Green and Ryan 1972). Although an involve-
ment of wound-induced electrical signals was immediately suspected and
tested (Pickard 1973; Van Sambeek and Pickard 1976), it took 20-30 years
before the relationship was independently confirmed (Wildon et al. 1992;
Malone et al. 1994; Herde et al. 1995, 1996; Stankovic and Davies 1996, 1998).
20.2
Propagating Depolarization Signals in Plants
Three different types of propagating depolarizations in plants have been
suggested to reflect three different types of signals: APs, slow wave potentials
 
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