Mitochondrial and peroxisomal beta-oxidation capacities of organs from a non-oilseed plant.
Until recently, beta-oxidation was believed to be exclusively located in the peroxisomes of all higher plants. Whilst this is true for germinating oilseeds undergoing gluconeogenesis, evidence demonstrating mitochondrial beta-oxidation in other plant systems has refuted this central dogma of plant lipid metabolism. This report describes a comparative study of the dual mitochondrial and peroxisomal beta-oxidation capacities of plant organs. Oxidation of [1-(14)C] palmitate was measured in the cotyledons, plumules and radicles of Pisum sativum L., which is a starchy seed, over a 14 day period from the commencement of imbibition. Respiratory chain inhibitors were used for differentiating between mitochondrial and peroxisomal beta-oxidation. Peroxisomal beta-oxidation gave a steady, baseline rate and, in the early stages of seedling development, accounted for 70-100% of the beta-oxidation observed. Mitochondrial beta-oxidation gave peaks of activity at days 7 and 10-11, accounting for up to 82% of the total beta-oxidation activity at these times. These peaks coincide with key stages of seedling development and were not observed when normal development was disrupted by growth in the dark. Peroxisomal beta-oxidation was unaffected by etiolation. Since mitochondrial beta-oxidation was overt only during times of intense biosynthetic activity it might be switched on or off during seedling development. In contrast, peroxisomes maintained a continuous, low beta-oxidation activity that could be essential in removing harmful free fatty acids, e.g. those produced by protein and lipid turnover.
Masterson
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Department of Biological and Nutritional Sciences, University of Newcastle upon Tyne, Newcastle upon Tyne NE1 7RU, UK. christine.masterson@ncl.ac.uk
Wood
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D042962:Acyl-CoA Oxidase; D044943:Fatty Acid Desaturases / Q000037:antagonists & inhibitors; D008928:Mitochondria / Q000378:metabolism*; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000037:antagonists & inhibitors; D010168:Palmitates / Q000378:metabolism*; D018532:Pisum sativum / Q000378:metabolism*; D020675:Peroxisomes / Q000378:metabolism*; D012639:Seeds / Q000378:metabolism
D010168:Palmitates; D010088:Oxidoreductases; D044943:Fatty Acid Desaturases; D042962:Acyl-CoA Oxidase