Long-Distance Signal Transmission in Trees - Communication in Plants: Neuronal Aspects of Plant Life - page 333

23 Long-Distance Signal

Transmission in Trees
Stefano Mancuso, Sergio Mugnai

Abstract Long-distance transmission of signals is a critical event in the life of trees.
Many physiological studies have deduced that hormone-like substances together with hy-
draulic/electrical signals mediate this important function of the plant life. However the
nature of the complex network of signalling in trees has remained essentially unexplored.
Recent molecular and genetic studies offer new approaches to understanding the mecha-
nisms underlying the transmission of signals.

23.1
Introduction

The ability to sense and respond to environmental parameters is one com-
mon feature of living being. This talent is particularly significant in land
plants because of their necessity to manage all the environmental informa-
tion and stimuli without escaping. Among plants, trees, for their necessity
to respond in a short time to environmental stimuli despite the often big
dimensions, are the most obvious and interesting subjects of study for the
long-distance signal transmission.
Trees live in a continuously changing environment and although not all
parts of the tree are exposed to the same stimuli at the same time, different
parts of it respond in a coordinated fashion, demonstrating the existence of
communication between various regions of the tree. For years, researchers
have concentrated their efforts on the study of chemical (hormonal) signals
in trees, neglecting the fact that plants also use and rely on electrical and
hydraulic signals. In addition, it is especially in big plants such as trees
that the need for signals other than hormones becomes more important.
Considering the large leaf area of a tree, enormous amounts of chemicals
would need to be synthesized and transported in order to respond to
a signal coming from the roots. In contrast, both electrical and hydraulic
signals consume no chemicals in their propagation.
Here, “long distance” will refer to signals running for distances that can-
not be covered in reasonable times (a few hours) by diffusion in the aqueous
phase, and that often have to cover several metres as in the case of root-to-
shoot communication. For a long time, plant physiologists have presumed
that signalling systems in plants must involve transport of “something”
through the vascular system, effectively ignoring any other kind of signal