Similarities Between Endocannabinoid Signaling in Animal Systems and N-Acylethanolamine Metabolism in Plants - Communication in Plants: Neuronal Aspects of Plant Life - page 207

ical effects in animals, including satiety (LoVerme et al. 2005) and anti-
inflammatory responses (Fowler 2003), respectively. Some of the cellular
processesmediatedbyNAEsappeartobemediatedbybothreceptor-
dependent and receptor-independent pathways. For example, anandamide
bindingtoCB1receptorsisknowntostimulateG i / o proteins, which in
turn influences the activity of a series of second messengers and proteins,
including adenylate cyclase, voltage-gated calcium channels, K + channels,
phosphatidyl 3-kinase and mitogen-activated protein (MAP) kinase (De
Petrocellis et al. 2004; De Fonseca et al. 2005). On the other hand, experi-
ments with mouse cell cultures showing that NAE induction of transcrip-
tion and MAP kinase phosphorylation are not inhibited by G i / o protein
blockers or CB1 receptor antagonists can be taken as evidence for receptor-
independent signaling (Berdyshev et al. 2001).
The widespread occurrence of NAEs in various plant species (Chapman
2004), the recent cloning of a plant enzyme involved in the hydrolysis of NAE
(Shrestra et al. 2003) and the identification of high-affinity NAE binding
proteins in plant tissues whose binding appears to be influenced by CB
receptor antagonists (Tripathy et al. 2003) point to intriguing parallels to
mammalian endocannabinoid signaling. In this chapter, we review progress
in plant NAE research focusing on metabolism and prospective functions
while highlighting avenues for future work with the hope of generating
excitement in this emerging field within plant physiology.
14.2
NAE Structure and Occurrence in Plants
NAEs are fatty acid derivatives with amide linkages to ethanolamine
(Fig. 14.1). As such, they are electrically neutral, and as expected have
limited solubility in aqueous solutions. Various NAE types have been iden-
tified in animals (Schmid et al. 1990), higher plants (Chapman 2004) and
some microorganisms (Schmid et al. 1990). For the most part the acyl
moieties of NAEs are a reflection of the fatty acid compositions of the
parent organisms, although the precise profiles (and quantities) of NAEs
in a given organism vary from tissue to tissue. Generally NAEs are present
in amounts approximating nanograms per gram of fresh weight, but under
certain pathological conditions, NAE levels accumulate to micrograms per
gram of fresh weight (Schmid et al. 1990; Chapman 2004). This is particu-
larly striking under conditions of ischemia in mammalian heart and brain,
where NAEs accumulate in damaged tissues, but are barely detectable in
nearby unaffected tissues (Schmid et al. 1990).
In plants, NAEs were first identified in processed, seed-derived prod-
ucts in the 1950s, but not until the 1990s did it become evident that