Similarities Between Endocannabinoid Signaling in Animal Systems and N-Acylethanolamine Metabolism in Plants - Communication in Plants: Neuronal Aspects of Plant Life - page 215

step toward determining whether NAE receptors are responsible for medi-
ating NAE effects during plant defense signaling.

14.4.2
NAE in Seed Germination and Seedling Growth

NAEs and their precursor NAPEs are actively metabolized during seed
germination (Sandoval et al. 1995; Chapman et al. 1999; Shrestha et al.
2002), raising the possibility that the rapid metabolism of these fatty acid
ethanolamides during seed imbibition is necessary for the establishment
of normal seedling growth. Indeed, one of the more dramatic biological
effectsofNAEsinplantsistherecentobservationthatexogenousNAE12:0
impairs normal seedling development in Arabidopsis .Thesedefectsin
seedling development included a reduction in primary root elongation,
inhibition of root hair initiation and an alteration of cell division patterns
in the root meristem. The disruption of normal root development was
reflected at the cellular level as defects in endomembrane dynamics, and
microtubule and actin organization (Blancaflor et al. 2003; Motes et al.
2005). Interestingly, 1-butanol, a nonselective inhibitor of PLD because it
blocks the transphosphatidylation reaction catalyzed by all PLDs, is capable
of inducing similar defects in root development as NAE12:0 (Gardiner et
al. 2003; Motes et al. 2005). The previously mentioned studies suggest
that some of the physiological effects of NAE on seedling development
could be related to impaired PLD function. Indeed, downregulating PLD ζ

through interference RNA induces abnormalities in root hair development
(Ohashi et al. 2003) and knockouts to a gene involved in PC synthesis,
an intermediate lipid in the synthesis of PA by PLD, leads to defects in
root development (Cruz-Ramirez et al. 2004). The effect of 1-butanol on
the organization of the microtubule cytoskeleton has been suggested to be
the result of a two-step transphosphatidylation reaction catalyzed by PLD
(Dhonukshe et al. 2003).
Perhaps a more convincing argument supporting PLD as a target of NAE
during seedling development is a report showing that NAEs are potent,
noncompetitive inhibitors of PLD

α activity in vitro. Consistent with these

results is the observation that low concentrations of NAE inhibit abscisic
acid induced stomatal closure in leaf epidermal peels (Austin-Brown and
Chapman 2002), a process that is known to be mediated by PLD α (Zhang

et al. 2004). A closer analysis of the effects of 1-butanol and NAE on specific
cellular processes as well as studies of single or multiple PLD knockouts
(Wang 2002) particularly with regard to their responses to NAE should
provide clues as to how NAE interacts with PLD in modulating seed germi-
nation.