In Vivo Incorporation of Radioactive Metabolites by Golgi Apparatus and Other Cell Fractions of Onion Stem

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Abstract
Incorporation in vivo of various (14)C-labeled substrates into dictyosomes of onion (Allium cepa) stem was determined, and comparisons were made with other cell fractions on a nitrogen basis. Tissue explants were incubated for varying times in the presence of the radioactive metabolites supplied in the external medium. Fractions were then obtained from homogenates stabilized with glutaraldehyde. Purified fractions containing dictyosomes (individual stacks of cisternae) of the Golgi apparatus were obtained by centrifugation in a sucrose gradient also yielding a smooth membrane fraction free of dictyosomes. Dictyosomes were preferentially labeled with choline-1,2-(14)C and acetate-2-(14)C, suggesting that plant Golgi apparatus participate in the synthesis or modification of membrane lipids. Dictyosomes were also labeled with glucose-U-(14)C and leucine-U-(14)C, but on a molar basis incorporation was less than with choline or acetate.