Abstract: Abstract: 【Objective】The purpose of this research was to reveal the size-distribution characteristics of starch granules in wheat endosperm and to study the effect of different-stage shading on the size distribution of wheat starch granules.【Method】In this study, we used a self-made tent to shade wheat plants under field conditions, selected two strong-gluten wheat cultivars: GC8901 and JN17, and set four shading stages: flagging to flower, 1-10, 11-20 and 21-30 days after anthesis(DAA) to study the changes of number, volume and surface area distribution of starch granules in wheat endosperm.【Result and conclusion】The results showed that wheat endosperm had a unimodal curve in starch granule number distribution, and a bimodal curve in starch guanule volume or surface area distribution. On average, B-type granules (diameter<10µm) made up to 99.89% of the totle number of starch granules in wheat endosperm, and accounted for 84.43% of the total starch surface area, but contributed only about 46.85% of the total starch volume. On the other hand, A-type granules (diameter≥10µm) made up to 0.11% of the totle number of starch granules in wheat endosperm, and accounted for 15.57% of the total starch surface area, but contributed about 53.15% of the total starch volume. Size distribution of starch granules in wheat endosperm were influenced markedly by different-stage low light after flagging stage. Low light in 11-20 DAA could decrease the number of A-type starch granules in wheat endosperm, but the other shading treatment influenced it slightly. Low light influenced the inner size distribution of B-type starch granules significantly , and the influence varied with shading time, genotype and grain position in wheat spike. After shading from flagging stage to flower stage, the number of BS-type granules (diameter<1µm) decreased and BL-type granules (diameter 1~10µm) increased in GC8901 superior grains, but those changes in GC8901 inferior grains were on the contrary. The number distribution of starch granules in JN17 superior grains was influenced slightly by shading from flagging stage to flower stage, but in JN17 inferior grains BS-type granules number decreaed and BL-type granules increased. Shading from 1 DAA to 10 DAA increased the number of BS-type granules in wheat endosperm, but low light in the middle or latter grain filling stage increased BL-type granule number, and the function of middle grain filling stage shading was higher than latter grain filling stage shading. The volume and surface area percents of B-type starch granules in the endosperm of two wheat cultivars were increased after shading from 1 DAA to 10 DAA, but those in A-type granules were decreased. After shading from flagging stage to flower stage and low light from 11 DAA to 30 DAA, the volume and surface area percents of A -type starch granules increaesd but those in B-type granules decreased.

Key words: Wheat (Triticum aestivum L.), Starch, Low light, Size distribution