Effects of glucose starvation on the oxidation of fatty acids by maize root tip mitochondria and peroxisomes: evidence for mitochondrial fatty acid beta-oxidation and acyl-CoA dehydrogenase activity in a higher plant.
Fatty acid beta-oxidation was studied in organellar fractions from maize root tips by h.p.l.c. and radiometric analysis of the products of incubations with [1-14C]octanoate and [1-14C]palmitate. In crude organellar fractions containing both mitochondria and peroxisomes, octanoate and palmitate beta-oxidation, as determined by the production of acetyl-CoA, was functional and, for palmitate, was activated 4-12-fold after subjecting the root tips to 48 h of glucose starvation. The sensitivity to a 'cocktail' of respiratory-chain inhibitors containing cyanide, azide and salicylhydroxamate depended on the conditions of incubation, with no inhibition in a medium facilitating peroxisomal beta-oxidation and a significant inhibition in a medium potentially facilitating mitochondrial beta-oxidation. Indeed, preparations of highly purified mitochondria from glucose-starved root tips were able to oxidize octanoate and palmitate to give organic acids of the tricarboxylic acid cycle. This activity was inhibited 5-10-fold by the above cocktail of respiratory-chain inhibitors, with no parallel accumulation of acetyl-CoA, thus showing that the inhibition affected beta-oxidation rather than the pathway from acetyl-CoA to the organic acids. This provides the first evidence that the complete beta-oxidation pathway from fatty acids to citrate was functional in mitochondria from a higher plant. Moreover, an acyl-CoA dehydrogenase activity was shown to be present in the purified mitochondria. In contrast with the peroxisomal activity, mitochondrial beta-oxidation showed the same efficiency with octanoate and palmitate and was strictly dependent on glucose starvation.
Dieuaide
M
M
INRA, Centre de Recherche de Bordeaux, Villenave d'Ornon, France.
Couée
I
I
Pradet
A
A
Raymond
P
P
D000105:Acetyl Coenzyme A / Q000378:metabolism; D042964:Acyl-CoA Dehydrogenase; D044944:Acyl-CoA Dehydrogenases / Q000378:metabolism*; D002210:Caprylates / Q000378:metabolism*; D002250:Carbon Radioisotopes; D002458:Cell Fractionation; D002499:Centrifugation, Density Gradient; D002851:Chromatography, High Pressure Liquid; D003065:Coenzyme A / Q000378:metabolism; D005947:Glucose / Q000378:metabolism*; D008830:Microbodies / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D010084:Oxidation-Reduction; D019308:Palmitic Acid; D010169:Palmitic Acids / Q000378:metabolism*; D011865:Radioisotope Dilution Technique; D003313:Zea mays / Q000378:metabolism*
D002210:Caprylates; D002250:Carbon Radioisotopes; D010169:Palmitic Acids; D019308:Palmitic Acid; D000105:Acetyl Coenzyme A; D044944:Acyl-CoA Dehydrogenases; D042964:Acyl-CoA Dehydrogenase; D005947:Glucose; C031492:octanoic acid; D003065:Coenzyme A