The free amino‐acids and peptides of plant tissues

Abstract Free amino‐acids were extracted from pasture plants with 80% alcohol, and the residue was extracted with water to remove bound amino‐acids (peptide fraction). The alcohol extracts and the hydrolysed water‐extracts were assayed microbiologically for 17 amino‐acids. Total amino‐nitrogen was also estimated in these extracts by Van Slyke's nitrous acid method. Most of the free amino‐nitrogen was due to relatively few amino‐acids, chiefly the dicarboxylic acids (and their amides), alanine and serine. A larger number of amino‐acids contributed significantly to the peptide fraction. Treatment of the grasses with different nitrogenous fertilizers resulted in some differences in the amino‐acid patterns. Larger differences were noted between young and more mature tissues. Of the total amino‐nitrogen measured by Van Slyke's method about 70% in the free amino‐acid fraction and about 95% in the peptide fraction were accounted for by assay of individual amino‐acids.