Control of Enzyme Activities in Cotton Cotyledons during Maturation and Germination

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Abstract
Microbodies were isolated by zonal-rotor sucrose density gradient centrifugation from cotton (cv. DP 61) seeds at 2 distinct stages of embryogenesis (38 and 50 days after anthesis) and after 48 h postgerminative growth. In all cases, .beta.-oxidation activity (palmitoyl-coenzyme A (CoA)-dependent reduction of acetylpyridine adenine dinucleotide or production of acetyl-CoA) and activities of the enzymes palmitate:CoA ligase, acyl-CoA oxidase, enoyl hydratase, 3-hydroxyacyl-CoA dehydrogenase and 3-oxoacyl-CoA thiolase, plus catalase, were localized exclusively in the microbody fractions, i.e., none of the activities was associated with mitochondria. Acyl-CoA dehydrogenase activity was not detected in any gradient fractions or in homogenates. Glyoxysomes isolated from cotyledons of 48-h germinated seeds were capable of .beta.-oxidation of acyl-CoAs of various chain lengths and degrees of unsaturation and were the sole site of 3-cis-2-trans enoyl-CoA isomerase activity. Direct measurement of the isomerase is the first demonstration of an enzyme required for unsaturated fatty acid catabolism in a higher plant. Palmitoyl-carnitine was not oxidized by any organelle fraction. Subfractionation of glyoxysomes by osmotic shock revealed that none of the .beta.-oxidation enzymes were tightly membrane-associated.