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Evidence that amylose synthesis occurs within the matrix of the starch granule in potato tubers
Author(s) -
TATGE H.,
MARSHALL J.,
MARTIN C.,
EDWARDS E. A.,
SMITH A. M.
Publication year - 1999
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1046/j.1365-3040.1999.00437.x
Subject(s) - amylose , granule (geology) , amylopectin , starch synthase , starch , chemistry , biochemistry , botany , biology , paleontology
Transgenic potatoes expressing reduced levels of granule‐bound starch synthase I (GBSSI) have been used to investigate whether the synthesis of amylose occurs at the surface of the starch granule or within the matrix formed by the synthesis and organization of amylopectin. Amylose in these potatoes is wholly or largely confined to a central region of the granule. Consequently this core region stains blue with iodine whereas the peripheral zone stains red. By making extensive measurements of the relative sizes of the granules and their blue‐staining cores in tubers over a range of stages of development, we have established that the blue core increases in size as the granule grows. The extent of the increase in size of the blue core is greater in potatoes with higher levels of GBSSI. These data show that amylose synthesis occurs within the matrix of the granule, and are consistent with the idea that the space available in the matrix may be an important determinant of the amylose content of storage starches.