Synthesis of Limit Dextrinase in Germinated Barley Kernels and Aleurone Tissues

Abstract

The development and secretion of α-amylase and limit dextrinase activities in de-embryonated half-kernels of Harrington barley, incubated in the presence and absence of gibberellic acid (GA3), were studied. Development of the enzymes in germinated barley was also investigated. Enzyme levels in the aleurone and starchy endosperm tissues of half-kernels and germinated barley were measured, and proportions of limit dextrinase in aleurone and starchy endosperm tissues of different barley varieties were determined. Aleurones of de-embryonated barley half-kernels produced low levels of both α-amylase and limit dextrinase in the absence of GA3, although secretion of the enzymes from the aleurones under these conditions did not appear to be significant. Added GA3 enhanced the development of both enzymes in half-kernels as well as in germinated seeds. Secretion of α-amylase from aleurones of germinated seeds and de-embryonated half-kernels in the presence of GA3 was very rapid, but GA3 did not appear to have an effect on the secretion of limit dextrinase from aleurones, which was very slow in both de-embryonated half-kernels and germinated barley. The total limit dextrinase activity, and the proportions of limit dextrinase found in the aleurone and starchy endosperm tissues, varied in different varieties of barley.