Subcellular Localization of Enzymes involved in Lecithin Biosynthesis in Maize Roots

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Abstract
Sauer, A. and Robinson, D. G. 1985. Subcellular localization of enzymes involved in lecithin biosynthesis in maize roots.—J. exp. Bot. 36: 1257–1266. The distribution of several enzymes involved in phospholipid biosynthesis in growing primary roots of maize seedlings has been investigated. Whereas the terminal enzyme in lecithin biosynthesis, CDP-choline: phosphorylcholine diglyceride transferase, as well as glycerophosphate acyltransferase are primarily membrane-bound with activities being similarly distributed between endoplasmic reticulum and Golgi apparatus-rich fractions, more than two-thirds of the activity of phosphoryicholine CTP: cytidyl transferase is found in the cytosol. The remainder of this enzyme is almost exclusively associated with fractions rich in Golgi apparatus membranes. In addition, minor activities for both of the lecithin biosynthetic enzymes were found localized in the inner mitochondrial membrane. Attempts at inducing a translocation of cytidyl transferase activity from the cytosol to the endoplasmic reticulum by incubation in vitro and in vivo with mixtures of unsaturated fatty acids inhibited all lecithin biosynthetic activities (membrane-bound and soluble) measured here. These results are discussed in terms of a relative autonomy for the Golgi apparatus in cellular phospholipid biosynthesis. Consequences for membrane-flow in plant cells are briefly considered.