N-Acylethanolamine (NAE) Profiles Change During Arabidopsis Thaliana Seed Germination and Seedling Growth Page: 9
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acylate the amino head group of PE and produce N-acyl PEs. A noteworthy competitive
pathway to hydrolyzation by AtFAAH is the oxidation of NAEs containing two or more
double bonds (e.g. NAEs 18:2, 18:3, etc.) by 13-lipoxygenase (LOX) to produce
ethanolamide oxylipins (e.g. NAE oxylipin (18:2), etc.).
Abscisic acid (ABA), a plant stress hormone, is a sesquiterpene first described in
the mid-1I960s similar to other phytohormones with its influence on an array of both
physiological and developmental events (Koornneef et al., 1998). In seeds, ABA is
implicated in the regulation of protein and lipid reserve accumulation, the acquisition of
desiccation tolerance, the inhibition of precocious germination and the induction of
primary dormancy (Liotenberg, 1999). After embryonic pattern formation is complete,
ABA concentrations rise while the embryo establishes dormancy and synthesizes storage
reserves. In seedlings, ABA acts antagonistic to gibberillic acid, and its levels drop to
allow for germination and post-germinative growth under normal circumstances. However
if seedlings are exposed to osmotic stress, ABA levels increase and they induce growth
arrest (Lopez-Molina et al., 2002). Endogenous ABA concentrations can rise and fall
dramatically in response to several abiotic stresses such as drought, high salinity and low
temperatures (Bonetta et al., 1998). Some of the ABA responses are long term and
involve changes in gene expression while others are rapid and involve the modification of
ion fluxes (Koornneef et al., 1998). For example, leaf ABA concentrations can increase
10- to 50-fold within a few hours of the onset of water deficiency and subsequent
rewatering will return the concentrations to normal over the same time period (Zeevaart
et al., 1988). So, in general, ABA is a negative regulator of germination and is activated
by a variety of environmental stresses.9
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Wiant, William C. N-Acylethanolamine (NAE) Profiles Change During Arabidopsis Thaliana Seed Germination and Seedling Growth, thesis, August 2006; Denton, Texas. (https://digital.library.unt.edu/ark:/67531/metadc5333/m1/14/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; .