Agriculture Reference
In-Depth Information
5
The Role of Root Apices in Shoot Growth
Regulation: Support for Neurobiology
at the Whole Plant Level?
Peter M. Neumann
Abstract
This chapter reviews the potential and actual role of plant neurobiological activity
for integrating function at the whole plant level. Some support is provided for the drawing of
analogies between the signaling roles of plant long-distance transport systems and animal
nervous systems. However, the specific findings reviewed here do not indicate that root
apices function as essential neurobiological command centers involved in regulating shoot
growth responses to adverse changes in the root environment.
5.1
Introduction
How cell and tissue activities give rise to integrated function at the level
of the whole organism is a central question in biology. Hormonal signal
molecules and the neurobiological activities of interconnected nervous
systems and brains can provide the needed integrative capacity in animals.
In plants, the activities of hormonelike substances are well characterized
but neither morphologically distinct brains nor anatomically distinct nerve
cells appear to have evolved. Nevertheless, it has been suggested by Baluska
et al. (2004a, b) that the transition zone in the growing root tip [which also
shows intense genetic (Birnbaum et al. 2003; Bassani et al. 2004), hormonal
(Aloni et al. 2004) and ionic activities (Peters and Felle 1999; Fasanao et
al. 2001; Fan and Neumann 2004)] together with the vascular transport
tissues (xylem and phloem) that interconnect with practically all the parts
of higher plants may be compared with the brains and nervous systems of
animals.
A criterion for a good hypothesis is that it stimulates thought and theo-
retical or experimental tests of validity: The suggestion that the root apex
of higher plants is part of a cell body that has neurobiological parallels and
can be viewed as a “diffuse plant brain” connected via vascular strands (the
“nerves”) to the plant shoot certainly meets this criterion.
When I, a plant stress physiologist, first considered the plant neurobiol-
ogyconcept,Iwasstimulatedtoclarifyformyselfthefunctionofnerves
and brains in animals and to evaluate the potential need for similar systems
in plants. I was also stimulated to look at the evolutionary progression of
plant morphology and anatomy in order to better evaluate the essentiality
to plant life of roots and vascular tissues serving as neurobiological entities.
Search WWH ::
Custom Search