Influence of mitochondrial β-oxidation on early pea seedling development

This work investigates the role of mitochondrial β-oxidation in early pea (Pisumsativum) seedling development using the epoxy fatty acid etomoxir. Etomoxir was used to effect selective chemical intervention in this biological system. The effect of this intervention on chloroplast structure and membrane composition was determined by transmission electron microscopy and lipidomic analysis by electrospray ionization (ESI) tandem mass spectrometry. β-oxidation was assayed radiochemically using 14C-palmitic acid. Chlorophyll and starch were assayed spectrophotometrically and lipid content determined by soxhlet extraction.Following emergence of the plumule, there was a switch from utilization of starch to lipid by the cotyledons. Etomoxir had a potent inhibitory effect on mitochondrial but not on peroxisomal β-oxidation. Seedlings grown hydroponically in 50 μM etomoxir in the light were phenotypically very different from water-grown controls. Chloroplast structure and fatty acid compositions were altered, etomoxir-treated plants containing more saturated fatty acids in their chloroplast lipids than controls. Etomoxir had no observable phenotypic effect on dark grown seedlings. When etiolated seedlings were exposed to light for 48 h, carnitine (on which mitochondrial β-oxidation depends)stimulated chlorophyll synthesis whilst etomoxir reduced chlorophyll synthesis. The development of newly emergent embryos into independent autotrophic seedlings is dependent upon mitochondrial β-oxidation in the cotyledons.