Starch Development And Its Relationship With Processing Quality In Wheat Varieties For Different End Uses

The experiments mainly studied the dynamic of starch content, observed the development of starch granules in grains of wheat for different end uses, analyzed the relationship of key enzymes involving in starch synthesis and sucrose content with starch content, discussed the relationship of starch and protein with processing quality and investigated the effects of cultivating measures on grain starch. The main results were as follows.1. Dynamics of grain starch accumulation in wheat varieties for different end uses were s tudied. T he results s bowed t hat a mylose, amylopectin a nd s tarch c ontents i n grains rose gradually after anthesis. The content increasing rate and accumulating rate of amylose appeared their maximum on the 25-30th day after anthesis (DAA) .While amylopectin content increasing rate and accumulating rate appeared on the 15-20th DAA and 20-25th DAA respectively. The ratio of amylose to amylopectin showed "V" type curve change. Starch content in weak-gluten wheat grains was higher than that in medium-gluten and strong-gluten wheat grains. Grain starch content and quality at different grain positions of the same variety were different. Grain starch and pasting parameters quality at the fourth position was the highest in a spikelet with four gains, but its weight was the lowest, so starch accumulation amount was the lowest.2. Starch granule structure was studied in grain endosperm cells both of weak-gluten wheat Ningmai 9, Yangmai 9 and strong-gluten wheat Zhongyou 9507, Yan 2801 from 2001-2003. The development of starch granules in grain endosperm of two types above was basically the same. Only did a few starch granules appear in endosperm cells on the 7th DAA. Mastoid protuberances started to appear on the surface of type I starch granules on the 9th DAA. Later mastoid protuberances seperated from type I starch granules and developed into typeIIstarch granules. The number of type II starch granules increased rapidly on the 21st DAA. Mastoid protuberance differentiation generally stopped after the 25th DAA, and type I and II starch granules continued to fill till grain mature. At the same position, the number of type II starch granules in weak-gluten-wheat grains was more than that in strong-gluten wheat grains from the 25th DAA to maturity.The number of type II starch granules in the abdomen was more than that in the dorsum in the same grain at maturity. N application amount and the ratio of basal to top dressing N had significant effects on size and number of type I and II starch granules. The treatment with greater N application amount or higher percentage of top dressing N had larger type II starch granules in grains.3. Changes of soluble sugar and sucrose contents in wheat plant and the activities of key enzymes i nvolving in starch biosynthesis in g rains were s tudied. The r esults showed that SPS activity in flag leaves declined after anthesis, and sucrose content in flag leaves decreased correspondingly. Sucrose content and the activity of SS for sucrose degradation in grains reached the maximum on the 10th DAA, then declined. Soluble sugar and sucrose contents in stems and leaf sheathes reached the maximum on the 15th DAA. Soluble sugar and sucrose contents in both basal intemodes and middle intemodes were higher than those in peduncles. Soluble sugar and sucrose contents in flag leaves, stems and sheathes, and grains were positively correlated with starch content. The activity changes of four key enzymes (AGPP SSS GBSS SBE)all showed a single peak curve. AGPP, SSS and SBE activities reached their peaks on the 25th DAA, while GBSS activity reached its maximum on the 30th DAA. The activities of AGPP, GBSS and SBE had significant correlations with amylose, amylopection and starch accumulating rate. The higher the four enzyme activities in grains (divided by grain weight) were, the higher the contents of starch and its components were. Four enzyme activities per unit grain weight in grains of weak-gluten wheat Yangmai9 were higher than those in grains of medium-gluten Ya...