4-methyleneglutamine in peanut plants: dynamics of formation, levels, and turnover in relation to other free amino acids

Abstract

Neither 4-methyleneglutamine nor 4-methyleneglutamic acid were found in free or bound form in ungerminated peanut seeds (Arachis hypogaea L.). Both, however, were formed soon after germination; whereas, 4-methyleneglutamic acid appeared slightly before 4-methyleneglutamine, the former remained at a low concentration while the level of 4-methyleneglutamine rose rapidly between 2 and 10 days of germination and declined slowly thereafter. Free proline and glutamine followed a pattern similar to 4-methyleneglutamine; on the other hand, asparagine increased for at least 20 days but other free amino acids remained at relatively low, constant levels. In mature peanut plants, 4-methyleneglutamine occurred in all parts except developing pods, was virtually the only free amino acid in xylem sap, and constituted about 70% of the total soluble nitrogen of sap. In contrast, 4-methyleneglutamic acid was found only in leaves and stems in highly variable amounts.Levels of 4-methyleneglutamine were largely independent of the processes of nodulation and nitrogen fixation. This amide was degraded much more slowly in nitrogen-deficient plants than were any of the other free amino acids and did not become labeled when a photosynthesizing plant was exposed to (14)CO(2) for 24 hours. The results indicate that 4-methyleneglutamine is the principle carrier of nitrogen in the xylem of peanut plants but its carbon skeleton appears to turn over very slowly.