The amylose and lipid contents of starch granules in developing wheat endosperm

Abstract

Starch was isolated from three varieties of wheat at various stages of grain development (endosperm filling) and separated by sedimentation into eight fractions according to granule size. Starch granule dimensions were measured using a Coulter Counter with 100-Channel analyser, and whole wheat and starch granule compositions were determined. At most stages of development the numbers of Agranules/endosperm remained constant while granule size increased, but the numbers of B-granules/endosperm increased throughout grain development. The amylose content (% dry weight) increased with granule size and with granule maturity, whereas lysophospholipid content (dry weight basis) generally decreased with granule size but increased with granule maturity. Starch deposited on individual large A-granules at successive stages of development contained higher proportions of amylose and lysophospholipids than initial deposits. Similarly, small B-granule starch synthesised at successive stages of grain development contained more amylose and lysophospholipids than the earlier B-granule starch. It was calculated that there should be gradients of amylose and lysophospholipid composition along the outer radii of A-granules, and similar changes in successive populations of B-granules. It is concluded that there was a close relationship between amylose content and lysophospholipid content in the developing A-granules and in the developing B-granules in the starch of each wheat variety, but that this relationship was always different for the A- and B-granules.