Development of Caryopsis and Starch Physicochemical Properties in Different Grain Positions of Wheat Spikelets

Background: Spikelets at different spike positions and the caryopsis at different grain positions grow and develop differently. The caryopsis development and physicochemical properties of starch at different grain positions (the first, second, and third grain positions: G1, G2, and G3) of wheat spikelets were investigated in this study. Results: : During the development process, the thickness of both dorsal and abdomen pericarp 8 days after anthesis (DAA) followed the sequence G2 < G1 < G3. However, at 14 DAA the thickness followed the dorsal sequence of G1 < G2 < G3 and the abdomen sequence of G2 < G1 G2 > G3. In mature caryopsis, the caryopsis size and weight indicate that G1 = G2 > G3. The starch content followed the order G1 > G2 > G3, while the essential amino acid, the total amino acid, and the protein content followed the order G2 > G1 > G3. The apparent amylose content followed the sequence G3 > G2 > G1, and A-type starch content followed G3 > G1 > G2. The amorphous ratio followed the order G2 > G1 > G3, whereas the double-helix ratio and the relative crystallinity exhibited the opposite trend. The order of the final degree of hydrolysis through AAG, PPA, and HCL was G2 > G1 > G3. Conclusions: : The different material contents were possibly due to the short development time of caryopsis, and the difference in starch physicochemical properties between G2 and the other grain positions might be related to the components and structural characteristics of starch.