Observations on the Germ Aleurone of Barley. Morphology and Histochemistry

The germ aleurone over the embryonic axis of barley was examinedin strips of tissue peeled off harvest-ripe grains. The germaleurone is only one cell thick but resembles 'normal' aleuronein being composed of living cells with dense, lipid-rich cytoplasmand thick walls containing phenolic material. In contrast tothe cells of the 'normal' aleurone, germ aleurone cells containvery few phytin or protein deposits. When the germ aleuroneis ruptured during germination, the walls at the torn edge becomethickened with shiny golden-brown material, and 'sealed' tothe testa. Two days after germination, lignin can be detectedin the walls of a single row of germ aleurone cells adjoiningthe scutellum. The role of the germ aleurone in defence againstmicroorganisms is discussed. It is suggested that the metabolicactivities in the germ aleurone in imbibed grains compete withthe embryo for oxygen, and thus may be one of the factors whichdetermine whether a grain germinates or remains dormant.Copyright1994, 1999 Academic Press Barley, Hordeum vulgare L., germ aleurone, histochemistry, defence mechanism, lignin, dormancy, microorganisms, pre-mature germination