Starch granule initiation and growth are altered in barley mutants that lack isoamylase activity.
Two mutant lines of barley, Risø 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 Risø 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.
Burton
Rachel A
RA
Department of Plant Science, University of Adelaide, Waite Campus, Glen Osmond, SA 5064, Australia.
Jenner
Helen
H
Carrangis
Luke
L
Fahy
Brendan
B
Fincher
Geoffrey B
GB
Hylton
Chris
C
Laurie
David A
DA
Parker
Mary
M
Waite
Darren
D
van Wegen
Sonja
S
Verhoeven
Tamara
T
Denyer
Kay
K
D000483:Alleles; D000595:Amino Acid Sequence; D001483:Base Sequence; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics; D017343:Genes, Plant; D005936:Glucans / Q000378:metabolism; D001467:Hordeum / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism* / Q000648:ultrastructure; D007517:Isoamylase / Q000235:genetics*; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D009154:Mutation; D018087:Plastids / Q000378:metabolism; D013213:Starch / Q000378:metabolism*
D018076:DNA, Complementary; D018744:DNA, Plant; D005936:Glucans; D013213:Starch; D007517:Isoamylase