DEVELOPMENTAL PATTERNS OF ENZYMES AND PROTEINS DURING MOBILIZATION OF ENDOSPERM STORES IN GERMINATING BARLEY GRAINS

Mobilization of stored reserves in the endosperm of barley grains involves the interaction of enzymes and other proteins synthesized during grain development and those synthesized during germination. In order to obtain information on this interaction, localization of alpha-amylase, the bifunctional subtilisin/alpha-amylase inhibitor (BASI). the unspecific lipid transfer protein (LTP), and the antimicrobial proteins chitinase and ribosome inactivating protein (RIP) were determined by immunofluorescence microscopy in the different tissues of resting and germinating grains of the Hordeum vulgare L. genotypes Alexis, Klages, and Steptoe. Targeting of alpha-amylase from the proximal to the distal part of the endosperm progresses with different rates in the three genotypes. LTP is localized in the endosperms, the aleurone layers and in the embryo of the ungerminated grains. LTP is depleted during the first days of germination but then re-synthesized in the embryo and in the aleurone during the following phases of germination and released to the endosperm independent of cell wall hydrolysis. Chitinase is present in the aleurone layers and, depending on variety, in variable amounts in the endosperm of the mature and the germinating grains. Secretion of chitinase from the aleurone and scutellum is indicated by the increasing amount found in the endosperm during germination. Chitinase accumulates in the distal aleurone layers before alpha-amylase is detected and thus must be able to penetrate the intact endosperm beta-glucan walls. BASI and RIP are localized in all parts of the mature grain and at later stages of germination the amount in the scutellum and aleurone layer increases. The analysed enzymes and proteins fulfill different functions during germination and are of importance for the industrial use of the barley crop. The efficient immunohistochemical demonstration of the genotypic variability in these characteristics provides a possibility to identify important breeding targets.