Peptide transport by embryos of germinating barley (hordeum vulgare)

Abstract

Two new fluorescent-labelling techniques for studying peptide transport are described. A peptide transport system has been demonstrated in a higher plant tissue, the scutellum of germinating barley embryos. This system has been extensively characterized, and found to have many similarities to peptide transport systems in microorganisms and mammalian tissues. Evidence has also been obtained for the existence of a peptide transport system in the membrane of an intracellular organelle, possibly the vacuole. Peptide transport is an active process and appears to require the production of a proton gradient across the plasmalemma. Disruption of the proton gradient not only inhibits peptide transport, but also causes general exodus of amino acids from the embryo and affects amino acid metabolism. Considerable pools of small peptides have been detected in both the endosperm and embryo of the germinating barley grain. The concentrations of peptides achieved in the endo sperm are of the right order of magnitude for the efficient operation of the peptide transport system. It seems that the uptake of small peptides by the scutellum of germinating barley embryos is of considerable importance in the transfer of nitrogen from the endosperm to the embryo during the iLobilization of zhe protein storage reserves.