References

26
Signals and Signalling Pathways
in Plant Wound Responses
JeremyD.Rhodes,JohnF.Thain,DavidC.Wildon
Abstract The focus is on the most widely studied wound response: the systemic synthesis
in tomato of the defence proteins known as proteinase inhibitors (PIs). In wounded tomato
seedlings, the severity of the wound is a major determinant of the type of wound signalling.
Minor wounds produce outcomes that are consistent with the transport in the phloem of
achemicalelicitorofPIsynthesis.Severewoundsproduceoutcomesthatareconsistentwith
the distribution of elicitors of PI synthesis and of electrical activity by hydraulic dispersal in
the xylem. The main electrical events associated with severe wounds are action-potentiallike
depolarisations in the sieve-tube-element/companion cell complexes; these events are
considered in relation to the use of the terms “action potential” and “variation potential”.
26.1
Introduction
Plants respond to wounding both locally at the wound site and at sites
distant from the wound (systemic responses). The most widely studied
response is the systemic synthesis of defence proteins, known as proteinase
inhibitors (PIs), in tomato seedlings following mechanical wounding, first
discovered by Green and Ryan (1972). Mechanical wounding has been
widely used to simulate insect damage. Our interest has been to elucidate
the nature of the signals and signalling pathways underlying this systemic
response. We believe that we can distinguish two situations: rapid signalling
following a severe wound, and signalling in the phloem following a minor
wound. The distinction between the effects of severe and minor wounds, in
our view, enables a synthesis of the published results from several different
research groups.
Severalcandidateshavebeenproposedasasignallinkingthelocalwound
to the systemic response, including both chemical and physical signals,
and a combination of the chemical and the physical: hydraulic dispersal.
Given the complex nature of a wound, Bowles (1998) has highlighted the
probability that such an event would give rise to multiple signals.
Possible chemical signals include oligosaccharides, jasmonic acid, and
the peptide systemin; all have been shown to be elicitors of PI synthesis
(Bowles 1998). Current evidence, based on mutations affecting PI synthesis,
favours jasmonic acid as being a systemic signal, with systemin acting locally
at or near the wound site – GA Howe’s group, using minor mechanical
Communication in Plants
F. Baluška, S. Mancuso, D. Volkmann (Eds.)
© Springer-Verlag Berlin Heidelberg 2006