Characterization Of Starch Property In Wheat And Its Relatives Seed, And Starch Synthesis In Oat Seed

As the major component in creal grains, starch provides nutrition and energy for human, animal, and serves as a function industrial material. Wheat{Triticum aestivum L.) as one of major crop in China has important application value for quality improvement. Oat as one of the six major crops in the world has a high commercial purposes. In this study, we focused on the differences in starch morphology, compostion and physicochemical properties in wheat and its relative, and analysed starch properties in different type of granules. We characterized starch granule development process and starch synthase gene expression during oat seed development. These findings will improve our understanding of starch synthesis pathway and characteristics of starch granules.Characterization of starch morphology, composition and physicochemical properties in wheat and its relatives1. Six accessions of wild diploid wheat,2 accessions of tetraploid wheat, and 3 hexaploid wheat lines were used in this study. We determined the starch morphology, size and distribution, and proportions of the A-type and B-type granules. The results indicate that the proportions of the A-type and B-type granules have significantly differences in different wheat genotypes. For example, the proportions of A-type granules in 2 accessions of Ae. speltoides were up to 44.2% and 45.1%.2. Amylose and total starch content, and amylopectin chain length distribution from A-type and B-type granules were analysed. Compare to etraploid wheat and hexaploid wheat,3 wild diploid species had significantly less total starch content. The amylose content of A-type granules was higher than that of B-type granules in accession of T. urartu, Ae. tauschii, T. durum, and hexaploid wheat. The A-type granules exhibited more number of B2 and B3 chains (DP 25 and up) but lesser number of A chain (DP 6-12) than did the B-type granules in different wheat genotypes.3. Based on gelatinization properties of A-type and B-type granules analysis, our results indicate that B-type granules had broader ranges of gelatinization Tc and (Tc-To) than the A-type granules did in different wheat genotypes. The Tp of A-type and B-type granules haven’t significantly in accession of TA1790, TA2402, AC Navigator, AC Avonlea and Chinese Spring, but the Tp of other species of B-type granules were higher than A-type granules. The B-type granules of T. urartu and T. aestivum showed larger gelatinization AH than the A-type granule counterparts did. The A-type granules showed higher retrogradation rates than the B-type granules did in different wheat genotypes.The investigation on development of starch granule and starch expressionssynthetase gene during the growth process of oat seed1. Using the scanning electron microscopy, we found that simple starch granules, including both A-type and B-type granule, appeared in the ovary of oat pericarps at 6 DPA. The A-type starch granules did not be detected in oat endosperm, indicating that the synthesis of starch granules in oat pericarp and endosperm may undertake different metabolic pathways. The unique compound granules were produced in oat endosperm at 10 DPA and then fragmented into irregular or polygonal simple granules from 12 DPA. We observed that the growth rings are discernible at 10 DPG, suggesting that the compound granules of oat starch were similar to A-type granules.2. Starch amylose content, amylopectin chain length distribution, and thermal properties analysis in three oat species were tested during seed development. The results showed that amylose contents, proportion of branch chain length of B1 chains (DPI3-24), gelatinization temperature, and retrogradation rates are gradually increased during the endosperm development, whereas the short A chains (DP6-12) are gradually decreased. The different genetic background and original regions may have led to these differences in structural characteristics and physicochemical properties among three varieties.3. We analyzed gene expressions patterns during oat starch synthesis by qRT-PCR in three oat species. We characterized 13 starch synthesis genes and separated these genes into three groups based on their distinct expression patterns. The first group, consisting of AGP-L, AGP-S, GBSSI, SSI, SSII, SSIII, SBEIIa and ISA, has a high level of gene expression at the early stage of endosperm development, reaching a peak at 15 DPA. followed by an abrupt decline. The second group, as exhibited by SBEI, and PUL, is characterized by low transcript level at the early stage, rapidly rises to its peak at 15 DPA, followed by a gradual decline until seed maturity. The two group (SSⅣ and SBEⅡb) is characterized by the low-level expression during whole endosperm development. The genes in the first group exhibit the increasing tendency on expressional level in the early stages while the rest genes of other groups showed the decrease in expressional through all states. Therefore, we conclude that the genes in the first group are critical in the initiation of starch synthesis.