Genetic elimination of a starch granule protein, SGP-1, of wheat generates an altered starch with apparent high amylose

A starch granule protein, SGP-1, is a starch synthase bound to starch granules in wheat endosperm. A wheat lacking SGP-1 was produced by crossing three variants each deficient in one of three SGP-1 classes. namely SGP-A1, -B1 or -D1. This deficient wheat (SGP-1 null wheat) showed some alterations in endosperm starch, meaning that SGP-1 is involved in starch synthesis. Electrophoretic experiments revealed that the levels of two starch granule proteins, SGP-2 and -3, decreased considerably in the SGP-1 null wheat though that of the waxy protein (granule-bound starch synthase I) did not. The A-type starch granules were deformed. Apparent high amylose level (30.8-37.4%) was indicated by colorimetric measurement, amperometric titration, and the concanavalin A method. The altered structure of amylopectin was detected by both highperformance size-exclusion chromatography and highperformance anion exchange chromatography. Levels of amylopectin chains with degrees of polymerization (DP) 6-10 increased, while DP 11-25 chains decreased. A low starch crystallinity was shown by both X-ray diffraction and differential scanning calorimetry (DSC) analyses because major peaks were absent. Abnormal crystallinity was also suggested by the lack of a polarized cross in SGP-1 null starch. The above results suggest that SGP-1 is responsible for amylopectin synthesis. Since the SGP-1 null wheat produced novel starch which has not been described before, it can be used to expand variation in wheat starch.