Molecular and physicochemical characterization of the high-amylose barley mutant Amo1

The synthesis of starch and the composition and structure of starch and the starch granules between Amo1 and its parental line Midas were compared. Staining of starch with 8-amino-1,3,6-pyrenetrisulfonic acid coupled with confocal laser scanning microscopy illustrated the high-amylose content of starch from Amo1 endosperm and visualized a prominent degree of cracking at the surface of the granules. The Amo1 starch exhibited a considerably higher content of covalently bound phosphate as compared to Midas, whereas the branch size distribution of the amylopectin molecules was similar in both cultivars. Expression of the genes encoding different starch synthesis enzymes in Amo1 appears more or less unaffected at both the transcript and protein levels. However, zymogram analyses clearly showed that the starch-branching enzyme (SBE) activity differed between the two cultivars, particularly at the early stage of endosperm development. A comparison of the starch granule proteomes of Amo1 and Midas revealed no differences with obvious relevance to starch synthesis but we found that the protein content of the Amo1 granules was higher than for Midas.