Description: The lipoxygenase (LOX) pathway plays an important role in the oxidative metabolism of polyunsaturated N-acylethanolamines (PU-NAEs). The LOX pathway functions in conjugation with hydrolysis by fatty acid amide hydrolase (FAAH) and to produce oxidized NAEs during seed germination and early seedling development. When Arabidopsis seedlings were grown in low micromolar concentrations of lauroylethanolamide (NAE 12:0), growth retardation and elevated endogenous PU-NAE levels were observed due to the competitive inhibition of LOX by NAE 12:0. The elevated levels of endogenous PU-NAEs were more pronounced in genotypes with reduced NAE hydrolase capacity (faah knockouts), and less evident with overexpression of FAAH. Alterations in PU-NAE metabolism were studied in seedlings of various lox and FAAH mutants. The partitioning of PU-NAEs into oxylipin metabolites was exaggerated in the presence of exogenous linolenoylethanolamide (NAE18:3) and resulted in bleaching of cotyledons. The bleaching phenotype was restricted to a narrow developmental window (3-to-5 days after sowing), and was attributed to a reversible disruption of thylakoid membranes in chloroplasts. Biochemical and genetic evidence suggested that 9-hydro(pero)xy and 13-hydro(pero)xy octadecatrienoylethanolamides (9- and 13-NAE-H(P)OT), but not their corresponding hydro(pero)xy free fatty acids, induced cotyledon bleaching. The LOX-mediated metabolites of NAE18:3 shared some overlapping effects on seedling development with those of linoleoylethanolamide (NAE18:2) such as a reduction in seedling root growth. On the other hand, NAE18:3 oxylipin metabolites also exhibited distinct effects during seedling development such as the inhibition of photomorphogenesis. Biochemical and genetic evidence indicated that a LOX-mediated metabolite of NAE18:2, 9-hydro(pero)xy octadecadienoylethanolamide (9-NAE-H(P)OD), acted as a potent negative regulator of seedling root development, and this depended on an intact abscisic acid (ABA) signaling pathway. Synergistic inhibition of root elongation between 9-NAE-H(P)OD and ABA was restricted to a narrow developmental window (3-to-5 d after sowing) of seedling development. Genetic evidence with Arabidopsis mutants in ABA synthesis (aba1, aba2), perception (pyr1, ...
Date: August 2015
Creator: Keereetaweep, Jantana
Item Type: Thesis or Dissertation
Partner: UNT Libraries