Abstract
Arginine-ε-15N2 was supplied to intact 1-year-old shoots of a 21-year-old satsuma mandarin tree, and arginine-ε-15N2, urea-15N2 and ammonium-15N were each fed to excised 2-year-old stem sections. The 15N was traced in the bark, wood, new shoots, and new leaves. Arginine-ε-15N2 was steadily metabolized via γ-guanidinobutyric acid in the bark and wood. The 15N of arginine was most markedly incorporated into the glutamine-amide N, but also into glutamine-amino N, alanine and γ-aminobutyric acid. Some 15N was also used for proline formation. The labelling patterns of amino compounds when urea-15N2 or ammonium-15N was fed were both similar to when arginine-ε-15N2 was fed. This finding strongly suggests that the 15N of arginine-ε-15N2 is used for amino compound synthesis via urea and/or ammonium. Arginine-ε-15N2 was translocated, and appeared in an unmetabolized form in new shoots where it was incorporated into protein. The 15N of arginine was also transferred to other amino compounds, and then incorporated into protein in new shoots. Several differences in N metabolism were found between the bark and wood: whatever the source of 15N, asparagine-amino N had a higher 15N enrichment than aspartic acid in the bark, but a lower enrichment in the wood. Glutamine, asparagine and proline were more actively synthesized and accumulated in the bark, while in the wood, arginine was.
