Role of granule-bound starch synthase in determination of amylopectin structure and starch granule morphology in potato.
Reductions in activity of SSIII, the major isoform of starch synthase responsible for amylopectin synthesis in the potato tuber, result in fissuring of the starch granules. To discover the causes of the fissuring, and thus to shed light on factors that influence starch granule morphology in general, SSIII antisense lines were compared with lines with reductions in the major granule-bound isoform of starch synthase (GBSS) and lines with reductions in activity of both SSIII and GBSS (SSIII/GBSS antisense lines). This revealed that fissuring resulted from the activity of GBSS in the SSIII antisense background. Control (untransformed) lines and GBSS and SSIII/GBSS antisense lines had unfissured granules. Starch analyses showed that granules from SSIII antisense tubers had a greater number of long glucan chains than did granules from the other lines, in the form of larger amylose molecules and a unique fraction of very long amylopectin chains. These are likely to result from increased flux through GBSS in SSIII antisense tubers, in response to the elevated content of ADP-glucose in these tubers. It is proposed that the long glucan chains disrupt organization of the semi-crystalline parts of the matrix, setting up stresses in the matrix that lead to fissuring.
Fulton
Daniel C
DC
Department of Metabolic Biology, John Innes Centre, Colney Lane, Norwich NR4 7UH, United Kingdom.
Edwards
Anne
A
Pilling
Emma
E
Robinson
Helen L
HL
Fahy
Brendan
B
Seale
Robert
R
Kato
Lisa
L
Donald
Athene M
AM
Geigenberger
Peter
P
Martin
Cathie
C
Smith
Alison M
AM
D000687:Amylopectin / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D002236:Carbohydrate Conformation; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D003594:Cytoplasmic Granules / Q000201:enzymology* / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D012542:Scattering, Radiation; D011198:Solanum tuberosum / Q000201:enzymology / Q000378:metabolism*; D013214:Starch Synthase / Q000302:isolation & purification / Q000378:metabolism*
D000687:Amylopectin; D013214:Starch Synthase