Nitrogen metabolism of Picea glauca. V. Metabolism of uniformly labeled 14C-L-proline and 14C-L-glutamine by dormant buds in late fall

Abstract

In early fall, the high levels of free arginine nitrogen in spruce buds were eventually replaced by proline nitrogen, and in late spring, glutamine nitrogen accumulated. In late October when levels of free proline nitrogen were high, bud primordia from terminal shoots were excised and exposed to uniformly labeled 14C-L-proline and 14C-L-glutamine. The main early products from 14C-L-proline were Δ1-pyrroline-5-carboxylic acid, glutamic-γ-semialdehyde, and glutamic acid. Later products included glutamine, γ-aminobutyric acid, and to a much lesser extent pyrrolidone carboxylic acid, ornithine, and arginine. In protein, radioactivity was recovered from proline, glutamic acid, and hydroxyproline.Products from 14C-glutamine were mainly glutamic and α-ketoglutaric acid as well as proline, γ-aminobutyric acid, alanine, and pyrrolidone carboxylic acid. In protein, glutamic acid, aspartic acid, and proline contained carbon-14. Results indicated that proline and glutamine were related by their carbon metabolism through a common path involving glutamic acid. However, the main feature of glutamine metabolism was the removal of its α-amino and the amide nitrogen to yield α-keto acids especially α-ketoglutaric acid. The occurrence of α-ketoglutaramic acid could have accounted for succinamic acid and succinimide derived from 14C-L-glutamine.