The Peptide Pools of Germinating Barley Grains: Relation to Hydrolysis and Transport of Storage Proteins

Abstract

A quantitative procedure for purifying small peptides from plant tissues, involving both ion-exchange and gel-exclusion chromatography, is described. Peptides were quantified and characterized by using the fluorescence reagents dansyl chloride and fluorescamine. Large pools of small peptides and amino acids have been identified in both the endosperm and embryo of germinating barley grains. The peptide pool of the endosperm increases during the first 3 days of germination, subsequently decreasing, an observation compatible with a role for peptides as intermediates in the breakdown of the storage proteins and their transfer to the embryo. The amino acid composition of these peptides indicates that all the major classes of storage protein contribute to the pool. The concentration of peptides produced in the endosperm during germination is sufficient for the efficient operation of the peptide transport system of the scutellar membrane characterized previously (Higgins and Payne, Planta 136: 71-76, 1977; Planta 138: 211-215 and 217-221, 1978). Data presented here indicate that peptides play at least as important a role as amino acids in the transfer of stored nitrogen from the endosperm to the embryo during germination.