The proteins released by isolated barley aleurone layers before and after gibberellic-acid treatment

Isolated barley (Hordeum vulgare L.) aleurone layers released a number of proteins into an aqueous medium in the absence of gibberellic acid (GA3). Evidence from molecular weight determinations and a number of immunological tests indicated that these proteins were water-soluble endosperm proteins which apparently arose from endosperm cells which adhered to the layers during isolation. They were not aleurone-cell proteins. By means of immunofluorescence, the water-soluble endosperm proteins were found to be concentrated around starch grains in the starchy endosperm. These proteins were resistant to hydrolysis by GA3-induced hydrolases released from aleurone tissue.Isolated aleurone layers could be washed free of soluble endosperm proteins. After treatment with GA3, such layers released another group of proteins which were shown by immunological and electrophoretic methods to be uncontaminated by soluble endosperm proteins. The pure GA3-induced proteins were separated, using SDS-acrylamide gel disc electrophoresis, into 12 components which had molecular weights (monomer) from 15500 to 81000. Ten of these protein bands became radioactive if GA3-treatment of layers was carried out in the presence of radioactive amino acids, and therefore probably contained de novo synthesized proteins. The two protein bands which were not labelled contributed about 40% of the protein released by washed aleurone layers after GA3 treatment, and their production appeared to be dependent on proteolysis.