Similarities Between Endocannabinoid Signaling in Animal Systems and N-Acylethanolamine Metabolism in Plants - Communication in Plants: Neuronal Aspects of Plant Life - page 205

14 Similarities Between Endocannabinoid

Signaling in Animal Systems
and N -Acylethanolamine Metabolism
in Plants
Elison B. Blancaflor, Kent D. Chapman

Abstract N -Acylethanolamines (NAEs) are minor lipid constituents of plant and animal
cells, and their roles in mammalian physiology and neurobiology have been studied inten-
sively for many years. However, corresponding studies on the function of NAEs in plants
have appeared only recently. Within the last decade significant progress has been made
in quantifying NAEs in plant tissues, characterizing their potential targets in plant cells
and identifying the relevant enzyme involved in their degradation, but much remains to
be determined regarding the role of these fatty acid amides in plant physiology. Although
our understanding of the specific functions of NAE in plants is far from complete, recent
advances in plant NAE biochemistry are pointing to intriguing similarities between animals
and plants in the metabolism and perception of NAE. In this chapter we discuss NAEs as
prospective signaling and regulatory molecules in plant cells. Advances in mammalian NAE
research are presented when appropriate in order to draw parallels as well as to highlight
differences between plant NAE metabolism and the endocannabinoid signaling system, the
major pathway by which NAE exerts its physiological effects in animal cells.

14.1
Introduction and Overview
of Mammalian Endocannabinoid Signaling

Formanycenturiesderivativesofmarijuana( Cannabis sativa )havebeen
known to possess medicinal properties. Identification of 9-tetrahydrocan-
nabinol (THC; Fig. 14.1a) as one of the active ingredients of marijuana
led to the discovery of a group of G-protein coupled receptors that bind
to THC. Two cannabinoid (CB) receptors, CB1 and CB2, have been cloned
thus far, with CB1 being the most highly expressed neuromodulatory re-
ceptor in the brain. CB2 receptors, on the other hand, are absent in the
brainbutpredominateintissuesoftheimmunesystem(WilsonandNicoll
2002). Low levels of N -acylethanolamines (NAEs) were first identified in
mammalian brain in 1965 (Bachur et al. 1965) but the function of this
family of lipids remained unclear until N -arachidonylethanolamine (anan-
damide; NAE20:4; Fig. 14.1b) was discovered to be an endogenous ligand
for CB1 receptors (Devane et al. 1992). This finding stimulated a flurry of
research on the metabolism and biological activities of NAEs in several
animal models, which eventually solidified the status of anandamide as
an endogenous neurotransmitter (Self 1999). Anandamide as a ligand for