Phospholipids in the Uredospores of Uromyces phaseoli: II. Metabolism during Germination

The levels and types of phospholipids changed in distinct phases during the germination of (32)P-labeled uredospores of Uromyces phaseoli. During the first 20 minutes of germination, the phospholipid content dropped to 40% of the pregermination level. Between 2 and 3 hours, phospholipid levels increased to approximately 80% of the pregermination levels, and after germination for 5 hours, catabolism had reduced the (32)P-lipids to about the same level observed prior to the first anabolic phase. A second anabolic phase was observed between 5 and 10 hours of germination. Phosphatidylcholine and phosphatidylethanolamine, the major phospholipids, did not undergo anabolism and catabolism at the same rates during germination. Only small quantities of the more polar phospholipids were released to the germination media.Germinating uredospores were capable of utilizing l-methionine-methyl-(14)C, d,l-(14)C serine, (14)C-choline, and (14)C-ethanolamine for the synthesis of phospholipids. The active one-carbon units from methionine and serine appear to be involved in the methylation of phosphatidylethanolamine to form phosphatidylcholine. Preformed ethanolamine and choline may be incorporated into these two phospholipids also. Evidence for the synthesis of phosphatidylserine, which is subsequently decarboxylated to yield phosphatidylethanolamine, was obtained.