The Fate of l-Phenylalanine Fed to Germinating Pea Seeds, Pisum sativum (L.) var. Alaska, during Imbibition.

Radioactive l-phenylalanine-l-(14)C or -U-(14)C was fed to pea seeds during imbibition. More than 95% was imbibed. Less than 1% of the radioactivity was respired as CO(2). Of the radioactivity taken into the embryos, 80% was still in the cotyledons by 3 days. About half of this was unchanged phenylalanine: 5% free, 10 to 20% in soluble proteins, 1 to 6% in cell wall proteins, and 14% released by mild acid hydrolysis. No other radioactive amino acid was found. About 0.3% of the radioactivity was identified as free caffeic, ferulic, and coumaric acids or their glycosides, and a further 5% was released by mild acid hydrolysis into a phenolic acid fraction. About half of the radioactivity in the cotyledons was lost in the fractionation procedures.About 20% of the radioactivity was found in the shootroot axes to which it had been translocated. Phenylalanine accounted for nearly all the identifiable radioactivity: about 1% free, 1 to 3% in soluble proteins, 1 to 5% in cell wall proteins, and 1% bound to insoluble fractions from which it was released by mild acid hydrolysis. About 1% was released into a phenolic acid fraction. About half of the radioactivity in the shoot-root axes was lost in the fractionation procedures.