Starch granule initiation and growth are altered in barley mutants that lack isoamylase activity

Abstract

SummaryTwo mutant lines of barley, Risù 17 and Notch-2, were found to accumulate phytoglycogen in the grain. Like the sugary mutants of maize and rice, these phytoglycogen-accumulating mutants of barley lack isoamylase activity in the developing endosperm. The mutants were shown to be allelic, and to have lesions in the isoamylase gene, isa1 that account for the absence of this enzyme. As well as causing a reduction in endosperm starch content, the mutations have a profound effect on the structure, number and timing of initiation of starch granules. There are no normal A-type or B-type granules in the mutants. The mutants have a greater number of starch granules per plastid than the wild-type and, particularly in Risù 17, this leads to the appearance of compound starch granules. These results suggest that, as well as suppressing phytoglycogen synthesis, isoamylase in the wild-type endosperm plays a role in determining the number, and hence the form, of starch granules.

The Effect of the Amount of Nitrogen Fertilizer on Starch Metabolism in Leaf Sheath of Japonica and Indica Rice Varieties during the Heading Period

“…In endosperm during grain fi lling of cereal plants, DBE probably play a crucial role in the starch synthesis (James et al, 1995, Nakamura et al, 1996Kubo et al, 1999;Burton et al, 2002;Dinges et al, 2003). As shown in Fig.…”

“…There are two types of DBE, pullulanase and isoamylase, that hydrolyze the α-1,6-glucosidic bond in amylopectin. In addition, it is accepted that DBE also plays an important role in starch synthesis (James et al, 1995;Nakamura et al, 1996;Kubo et al, 1999;Burton et al, 2002;Dinges et al, 2003). We examined the activity of pullulanase-type DBE in rice leaf sheath during the heading period (Fig.…”

“…However, analyses of mutants with the reduced starch content in endosperm in rice (Nakamura et al, 1996;Kubo et al, 1999), maize (James et al, 1995;Dinges et al, 2003), and barley (Burton et al, 2002) indicate that DBE plays a crucial role in the starch synthesis. Though a function of DBE in the rice leaf sheath is not clear, DBE may also be involved in the starch synthesis in leaf sheath.…”

Starch accumulation, activities of key enzyme and gene expression in starch synthesis of wheat endosperm with different starch contents

“…Studies in barley mutants and transgenic rice suggest that isoamylases play a crucial role in starch granule initiation (Burton et al 2002;Kawagoe et al 2005). In wheat, the cDNA expression of an isoamylase-type DBE (Iso-1) is the highest in developing endosperm and undetectable in mature grains, which suggesting a biosynthetic role for isoamylase in this tissue.…”

Recent progress toward understanding the role of starch biosynthetic enzymes in the cereal endosperm

“…Different levels of ISA activity, such as in maize (su1), barley (isa-1), and rice (sug-1), can result in a range of phenotypes associated with the endosperm, ranging from a mild phenotype of sugary amylopectin with more short chains, to a severe phenotype resulting in the replacement of amylopectin with phytoglycogen [91][92][93][94][95][96]. Rice, maize and barley sugary-1 (ISA1) mutants have shown heterogeneous distributions of starch and phytoglycogen in their endosperms, while Arabidopsis mutants of ISA1 and ISA2 display accumulation of phytoglycogen in the leach mesophyll and slightly altered amylopectin in the epidermal cells and vascular bundle-sheath cells [97.98].…”