Nitrogen metabolism of Picea glauca. III. Diurnal changes of amino acids, amides, protein, and chlorophyll in leaves of expanding buds

In spring, buds of spruce shoots under moisture stress contracted during the day and expanded at night. Increased water supply to roots removed the shrinkage of buds and stimulated rapid expansion. In leaves of buds about to break and under moisture stress, the alcohol-soluble nitrogen, high in arginine content, was maximal at midday, after midnight, and again at noon the next day. As a percentage of the soluble nitrogen, all compounds, except arginine, contributed most at sunset and again at sunrise. Other prominent amino acids included proline, alanine, γ-aminobutyric acid, and the amides glutamine and asparagine. Except for the amides, these and other compounds, present at lower levels, gave diurnal patterns similar on a fresh weight basis to arginine. Values for protein nitrogen were greatest at 2 p.m. followed by an increase of asparagine nitrogen, and again at 4 a.m., followed by an increase of glutamine nitrogen. At night the composition of newly synthesized protein increased significantly in aspartic acid, serine, glycine, alanine, leucine, and isoleucine. Chlorophyll a increased from 2 p.m. to 10 p.m., whereas chlorophyll b was present at lower levels and showed little diurnal variation.