The Studies Of Starch Synthesis And Programmed Cell Death During Grain Filling In Triticale

Triticale (X Triticosecale Wittmack) is an artificial cereal crop developed from the intersepcific cross between wheat (Triticum spp.) and rye (Secale cereale). It is a relatively new and adaptable crop. Triticale can be an excellent delivery platform for biomolecules or bioproducts because it is a low input crop with high grain yield and starch content potential However, triticale starch has not been comprehensively characterized yet, and consequently there is limited information available in public databases. In this study, the morphological features of triticale starch granules and their changes during endosperm development and seed germination were observed. Starch accumulation, expression of starch synthesis genes, programmed cell death during grain filling in triticale were also investigated.1. In order to investigate and compare the characteristics of starch granules in triticale, the morphological changes of starch granules were observed during seeds development, germination and enzymatic treatments using scanning electron microscopy. A- and B-type starch granules appeared to be bimodal size distribution in triticale. The pericarp tissue was a major site of starch deposition during early seed development. Starch granules were rapidly accumulating in triticale endosperm after 6 days post anthesis (DPA). During the seed germination, triticale starch was slowly degraded within 4 or 5 days post germination (DPG) and most starch granules were completely hydrolyzed after 9 DPG. There was a significantly positive correlation on the hydrolysis efficiency to the percentage of large granules in native starch granules. The equatorial groove and pits on the surface of triticale starch granules were more susceptible to the enzymatic hydrolysis than the broad or flat surfaces. The significant variations in the starch contents and compositions were observed among different triticale genotypes. There was a negative correlation on the swelling power to the diameters of native starch granules (r=-0.66, p≤0.05).2. The accumulation rate for grain weight, total starch and amylose per kernel, and the enzyme activities of AGPase, SSS, GBSS and SBE showed single-peak curves with the highest peak occurring during middle to late grain filling period. Correlation analyses indicated that kernel weight was closely related to amylose and amylopectin weight, respectively. Weight of amylose and amylopectin in single kernel were correlated or significantly correlated to the activities of key enzymes involved in starch biosynthesis, respectively. The major SGP were present 5 bands and in similar concentrations in isolated total or separated starch granules and no significant difference was observed among polypeptides with molecular weight lower than 60 kD at different developmental stages after anthesis in triticale. Numerous soluble endosperm proteins were detected and the protein concentration increased gradually to 30 DPA.3. The real-time PCR was used to analyze expression profiles of starch synthesis genes during endosperm development in triticale. The transcripts encoding ssⅠ, ssⅢand gbssⅠshared similar expression patterns from 9 DPA to 30 DPA in triticale endosperm. gbssⅡ, ssⅡ, sbeⅡa and sbellb genes exhibited a gradual down-regulation. The expression of sbel gene was gradually up-regulated from 6 DPA, with the highest average expression among the nine gene tested in this study. The relative expression of gbssll was lower than the other starch synthesis genes evaluated in this study. The average relative expression level of all the genes reached a maximum at 24 DPA.4. The development of triticale endosperm was companied by the progression of programmed cell death (PCD). The numbers of nuclei per endosperm in triticale reached the maximum level at 18 DPA. The evidence of DNA fragmentation was first observed at 21 DPA The pattern of starch accumulation rate and ABA content based on the single kernel showed similar unimodal curves during triticale grain filling. The ethylene production rate decreased after 15 DPA. The predicted amino acid sequences of Defender Against cell Death-1 (DAD-1) of partial plant and animal were homologous. The period between initial detection of PCD to its rapid increase overlaps with the stages of rapid starch accumulation during endosperm development. The timing and progression of PCD in triticale endosperm may interfere with starch synthesis and accumulation.