Mitochondrial and peroxisomal beta-oxidation capacities of organs from a non-oilseed plant

Until recently, beta -oxidation was believed to be exclusively located in t he peroxisomes of all higher plants. Whilst this is true for germinating oi lseeds undergoing gluconeogenesis, evidence demonstrating mitochondrial P-o xidation in other plant systems has refuted this central dogma of plant lip id metabolism. This report describes a comparative study of the dual mitoch ondrial and peroxisomal beta -oxidation capacities of plant organs. Oxidati on of [1-C-14]palmitate was measured in the cotyledons, plumules and radicl es 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. Pero xisomal beta -oxidation gave a steady, baseline rate and, in the early stag es of seedling development, accounted for 70-100% of the beta -oxidation ob served. 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 th ese times. These peaks coincide With key stages of seedling development and were not observed when normal development was disrupted by growth in the d ark. Peroxisomal beta -oxidation was unaffected by etiolation. Since mitoch ondrial beta -oxidation was overt only during times of intense biosynthetic activity it might be switched oil or off during seedling development. In c ontrast, peroxisomes maintained a continuous, low beta -oxidation activity that could be essential in removing harmful free fatty acids, e.g. those pr oduced by protein and lipid turnover.