| Wheat cultivars differing in spike type and quality type were used in the present study in 2004~2006 under different irrigation conditions and exogenous hormone experiments in Tai'an and Dezhou experimental locations. The granule size distribution, starch accumulation, plant hormones and related enzymes activities were investigated. The relationship between granule distribution, starch accumulation and process quality was also analyzed. The main results were as follows.1. The granule size distribution characteristic of wheat starch1.1 The starch granule size distribution of wheat cultivars differing in quality typeAt maturity, wheat contained two types of starch granules: smaller B-type granules(<9.8μm) and large A-type granules(>9.8μm). The diameter of starch granules changed in the range of 0.37～52.6μm. Volume distribution of starch granules showed the typical two populations with peak values in 5μm and 25μm, respectively. The number distribution of starch granules exhibited a single peak curve with peak at 1μm. The number of B-type starch granule comprised over 99% of the total starch granule numbers, indicating that the number of starch granules was mainly small starch granules. Similar to the volume distribution, the surface area distribution also showed double peak curves with peak at 2.8μm and 23μm. The B-type starch granules comprised about 80%, and A-type starch granules contributed about 20% of the total surface area.In 8 test cultivars, A-type starch granules composed 53.6～64.9% of the total volume. The cultivars that contained more A-type starch granules were LM21 and BY535, and the cultivars with little A-type starch granules were JN17 and 9818. It indicated that B-type starch granules volume percent was high in strong gluten wheat cultivars, and weak gluten wheat cultivars, LM21 and BY535, contained high A-type starch granules volume percent. Similar to the volume distribution, the surface area of B-type starch granules was lower in weak gluten wheat cultivars, LM21 and BY535, reached 79.0% and 79.4%, respectively. On the other hand, the surface area of B-type starch granules was higher in strong gluten wheat cultivars, 9818 and JM20, reached 83.8% and 82.2%, respectively. Compared with irrigation, rainfed conditions general raised the volume percent of B-type starch granules, and reduced that of A-type starch granules.1.2 The dynamic changes of starch granules in wheat endospermThe number of starch granules in wheat endosperm exhibited single peak curves with peaks at 0.5～1.1μm. At 7 DAA, the starch granules showed a broad band of variously sized granules up to 20μm diameter. The diameter band of starch granules enlarged to 30μm at 10 DAA. By 14 DAA, a burst of synthesis created a new population of small starch granules, which reduced the number proportion of big starch granules. At 17 DAA, starch granules in grain were mainly increased in volume. At 21 DAA, the number of starch granules less than 0.6μm increased sharply and that more than 0.6μm reduced evidently, indicating that a new distinct class of small granules was synthesized at this stage. From 24 to 28 DAA, the number of starch granules less than 0.6μm increased and bigger starch granules in diameter reduced continuously, indicating that new granules were still synthesized, however, the magnitude of increase reduced. At 35 DAA, it is mainly the enlargement of small granule size class diameter, not the other granule size class diameter.2. Starch accumulation and activities of related enzymes in wheat differing in quality typesAt irrigated and rainfed conditions, the starch content in weak gluten type cultivars were significantly higher than that in strong gluten type cultivars during grain filling period, indicating that weak gluten wheat had stronger ability of starch synthesis than strong gluten wheat. Compared with rainfed condition, the irrigation was more beneficial for the starch accumulation in both quality type cultivars.Activities of SPS, SS, UGPase, AGPase, SSS, GBSS and SBE in weak gluten type cultivars were significantly higher than those in strong gluten type cultivars during late grain-filling period, indicating that weak gluten wheat had stronger ability of starch synthesis and sucrose supply than strong gluten wheat at mid-late grain filling stage. Compared with irrigated plants, enhanced and reduced activities of related enzymes were observed in grains of plants subjected to soil water deficit in both quality type cultivars at early and mid-late filling stage, respectively. It is implied that rainfed condition was more beneficial for the improvement of starch synthesis ability at early filling stage, whereas irrigated condition was in favor of starch accumulation at late grain filling.3. Starch accumulation and activities of related enzymes in wheat differing in spike typesActivities of SS, AGPase, SSS, GBSS and SBE were significantly differed in two spike type cultivars. Under irrigated and rainfed conditions, activities of above enzymes in large-spike type cultivars were evidently higher than that in small-spike type ones during late grain filling period, which was the physiological mechanism for higher starch accumulation in large-spike type ones. The simulation with Logistic equation showed that it was accumulation duration and SAR that determined the starch accumulation in large-spike type cultivars.The effect of two planting conditions on two spike type wheat was different. The capacity to supply ADPG and the activities of relate enzymes in large-spike type cultivars at mid-late grain filling stage were significantly raised under irrigated condition. On the contrary, the soil water deficit led to a decrease in activities of key enzymes involved in starch synthesis, indicating that large-spike type cultivars were more sensitive to water deficit. On the other hand, rainfed conditions led to an increase at early grain-filling period and decrease during late grain-filling in small-spike type cultivars, respectively, in SAR and activities of key enzymes involved in starch synthesis, especially SS, AGPase, SSS, and SBE; however the magnitudes of the decrease were lower than those in large-spike type cultivars. This inferred that small-spike type cultivars were less sensitive to water deficit.4. Relationships of starch and process quality in different types of wheatThe starch pasting characteristics were evidently differed in different wheat cultivars. The values of peak viscosity, rough viscosity, final viscosity, setback, peak time and pasting temperature in strong gluten wheat, D99-3 and JM20, and weak gluten wheat, LM21 and BY535, were significant higher than other wheat cultivars. The strong gluten wheat 9818 has the lowest value of RVA parameters.The strong gluten wheat, JM20 and D99-3, had the highest noodle score. The next was weak gluten wheat, LM21 and BY535. The strong gluten wheat, 9818 and JN17, had the lowest noodle score. Strong gluten wheat generally has better palate, and weak gluten wheat has better color and appearance.TPA analysis showed that hardness, gumminess and chewiness in strong gluten wheat cultivars, D99-3, D3, JN17 and JM20, were evidently higher than those in weak gluten wheat cultivars, LM21 and BY535. Since above parameters were closely associated with palate and elasticity, noodles made of strong gluten wheat may has better palate and elasticity.5. Effects of exogenous plant hormones on accumulation of starch in wheat grains Under 6BA spraying treatment, the endosperm cell number, proliferation rate at medium-late cell division period, grain weight and starch accumulation in grains were significantly increased. Under irrigated conditions, the ratio of amylose/amylopectin in superior grains was also reduced which helpful for the improvement of starch quality; but 6BA had no obviously effect on the ratio of amylose/amylopectin in inferior grains. Under rainfed conditions, the starch content in superior and inferior grains in two wheat cultivars was raised by 6BA, but only the starch content in superior grains in JN17 was significant increased. The ABA treatment reduced the proliferation rate during mid and late cell division period and significantly decreased endosperm cell number in superior grains; but had no obviously effect on the reduction of endosperm cell number and grain weight in inferior grains. Compared with control, the ratio of amylose/ amylopectin had no significantly difference. Neither 6BA nor ABA spraying treatment changed the grains per spikes suggesting that exogenous plant hormones had no effects on the development of florets in wheat.6. Changes of endogenous plant hormones in grains of wheatUnder irrigated and rainfed conditions, the ZR and GA3 levels in weak gluten wheat were much higher than those in strong gluten wheat during late grain filling period, whereas, the difference of ABA levels in different type cultivars was not evident. In comparison with small-spike type cultivars, large-spike type cultivars possessed higher levels of IAA, ZR and GA3 at 7 DAA under irrigated and rainfed conditions. After 14 DAA, the difference of hormones levels became not evident. Large-spike type cultivars had higher ABA levels at late grain filling stage, corresponding to their higher grain filling rate at this stage.Compared with irrigated plants, enhanced and reduced levels of ZR, IAA and GA3 were observed in grains of plants subjected to soil water deficit at early and late filling stage, respectively. This infers that soil drought promoted cell division, ABA level and grain filling, whereas, water supply favored to enhance levels of ZR, IAA and GA3 during late grain filling period.
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