Effect of spikelet position on starch proportion, granule distribution and related enzymes activity in wheat grain

The starch proportion, starch granule distribution, and activities of enzymes involved in starch synthesis in different spikelet positions were examined during grain development in two high-yielding winter wheat cultivars. The results showed that grain number and weight per spikelet in different spatial position showed a single-peak curve from the base to the top in a wheat spike. Upper spikelets had the highest starch and amylose proportion followed by basal spikelets, whereas middle spikelets had the lowest. Starch and amylose absolute content was in opposition to their proportion. The volume of B-and A-type granule in grain of middle spikelets was remarkably higher and lower than those of basal and upper spikelets, respectively. However, no significant difference occurred in the number of A-and B-type granule in grains among different spikelet position. Compared with the basal and upper spikelets, the middle spikelets showed higher sucrose and ATP content and activities of starch biosynthetic enzymes, and subsequently higher starch absolute content. The results suggested that superior sucrose providing and degradation capacity and the high activities of enzymes involved in starch synthesis resulted in development of B-type starch granule in grain of middle spikelets.