| Two wheat cultivars, SN1391(soft winter wheat) and GC8901(hard winter wheat), were used for investigating the difference of yield and starch quality formation under different sowing date and effects of sowing date on starch granule development and starch composition accumulation process. To clarify the physiological basis and enzymological mechanism of starch quality formation, the high temperature, shading and temperature with light alternation experiments dealing with 2 wheat cultivars were conducted on the basis of sowing-date experiment. The principal results were as follows. 1. Effects of sowing date on yield and starch qulity formation in winter wheat 1.1 Yield and components of yield The effects of sowing date on yield and components of yield for the two cultivars were extremely significant.Both early-sowing and late-sowing reduced the kernel yield of SN1391, but that of GC8901 increased with the delay of sowing date.The genotype difference in response of kernel weight to sowing date existed among two varieties, with the earlier or later of sowing date, the kernel weights of SN1391 decreased but those of GC8901 increased. Summing up the effects of sowing date on yield and its components, we concluded that higher spike number and kernel weight were the basis for SN1391 to obtain high yield and keeping the balance of spike number, kernel number per spike and kernel weight was the premise of high yield for GC8901. 1.2 Process quality of flour and starch content Both early-sowing and late-sowing treatments increased the dough stability time, breakdown time and valormenter value of the two varieties, but early-sowing reduced the dough development time of GC8901.With the earlier or later of sowing date, the hold through, final viscosity, peak time and pasting temperature in SN1391 decreased too, but early-sowing increase the hold through, final viscosity, peak time and pasting temperature of GC8901, further more, late-sowing reduced the peak viscosity of GC8901. Amylose contents of late-sowing treatment in the two cultivars were minimum, but the responses of amylopectin content, total starch contents and ratio of amylopectin and amylose in the two cultivars were different. Both early-sowing and late-sowing reduced the amylopectin and total starch content and ratio of amylopectin and amylose of SN1391, but those of GC8901 increased gradually with the delay of sowing date. 1.3 Starch granule development and starch components accumulation process Shape, size and distributing of starch granule were affected significantly by sowing date. Few starch granules were found in the cortex thin wall cells of early-sowing treatment till 4 days after anthesis but some starch granules fell under our observation in the cells of 2 days post-anthesis of late-sowing treatment. Compared with the cortex thin wall cell, the starch granules in the outmost endosperm cell developed more earlier. The difference in shape and number of starch granule among the three treatments was found too. Only one to three starch granules, which looked like shuttle, existed in each plastid of the outmost endosperm cell of early-sowing treatment, but those in control and late-sowing treatments were more and bigger and the shape of them were circle or elliptical. At 8d after anthesis, the starch granule of early-sowing was maximal and that of natural-sowing was minimal but the starch granule number of late-sowing was maximum.The starch granules in endosperm cell were mainly concentrated on the position near the cell wall and there were fewer starch granule around the nucleolus by observing with microscope. Between the two tested wheat cultivars, the starch granule number of endosperm cell in SN1391 was more and bigger than that in GC8901. At the initial stages of starch accumulation, the starch granule of GC8901 was mainly concentrated on the one to five layer of endosperm within the pericarp thin-wall cell but in the five to eight layer of endosperm of SN1391, there still were more starch granules. Simulating with Richards Equation showed that it was initiating time and accumulation rate, but not accumulation duration that determined the finial contents of amylose and amylopectin in single grain under the condition of this experimentment . 1.4 Correlation of starch accumulation related with temperature and sunlight hour At early stages of starch accumulating, there was no significant effect of average sunlight hour and average air temperature of diurnal on the accumulations of amylose and amylopectin, but following the development of grain which showed a significant correlation. Regression analysis indicated that optimum average sunlight hours for amylose and amylopectin accumulation were 9.06 and 11.07 respectively and the optimum average air temperature ofdiurnal for amylopectin accumulation was 22.75℃. But the adaptive scope to temperature for amylose accumulation was very broad, when the mean temperature from 17 to 25℃, there was a positive correlation between amylose content and average air temperature of diurnal. 2 Effects of high temperature, shading and temperature with light alternation stress on yield and starch quality formation 2.1 Yield, components of yield and grain filling process High temperature,shading and temperature with light alternation treatment during different filling stages reduced the yield and had significant effect on components of yield, and the damage degree of high temperature and temperature with light alternation treatments at early grain-filling stages was higher than that at early and mid grain-filling stages. For the same cultivars, the determinative factor of kernel yield was kernel weight, but not spike number, grain number per spike and sterility spikelet number. Simulation the grain filling process with Logistic Equation showed that, after stressed with high temperature, shading and temperature with light alternation, it was the decrease of maximal filling rate and filling rate of slight-increase period that resulted in the reduction of kernel weight, and the filling duration, time of max. filling rate and filling rate of slow-increase period had little effect on kernel weight. 2.2 Starch quality of grain There was difference in the response of farimograph index to high temperature, shading or temperature with light alternation stress among the different varieties. The dough development time, breakdown time and valormenter value of SN1391 increased and the dough stability time decreased after high temperature stress at early filling stages. But the dough development time, stability time, breakdown time and valormenter value of GC8901 declined when the wheat were treated with high temperature,shading and temperature with light alternation stress. The peak viscosity, hold through and final viscosity also declined sharply after stressed by high temperature, shading and temperature with light alternation, and in SN1391, the treatment that those indexes declined extremely was J2 and that was T1 in GC8901. But which was S1 and S2 treatments of SN1391 and temperature with light alternation treatment of GC8901 that increased the crisp characteristic of ghee biscuit.2.3 Starch content and starch components accumulation The total starch and starch components contents of SN1391 were significantly decreased after stressed by high temperature,shading and temperature with light alternation at different filling stages, but the amylose, amylopectin and total starch contents of GC8901 increased after shading at early and mid grain filling stages. The ratio of amylopectin content and amylose content of J2 was lowest in both varities. Simulating with Richards Equation showed that it was weight at maximal accumulation rate (Wmax) determined the amylose and amylopectin accumulation under the adversity condition. 2.4 Sugar metabolism in flag leaves and grains 2.4.1 Total soluble sugar content, sucrose content and enzyme activities involved in sucrose metabolism in flag leaves The total soluble sugar content declined sharply after stressed by high temperature, shading and temperature with light interactant at early grain filling stages and increased at early and mid grain filling stages. Three days after stressed by high temperature and temperature with light interactant, the sucrose content in flag leaves increased and decreased after shading. Except for T1 and J1 of GC8901, the SPS and SS activities of others in flag leaves were reduced after stressed. But the AI and NI activities increased obviously except that the NI activity of S2 in SN1391 declined slightly. There was a positive correlation between sucrose content and SS and AI activities in flag leaves, and a negative correlation between sucrose content and SPS and NI activity. Except for NI, the correlations between SS, SPS and AI activities and sucrose content were extremely significant and the correlations coefficient was 0.742, -0.596 and 0.521 respectively. Which indicated that SS and AI were favorable during the sucrose accumulation and SPS took a key role of promoting the sucrose translation. Maybe NI was not the key enzyme invovled in sucrose metabolism in flag leaves. 2.4.2 Total soluble sugar content, sucrose content and enzyme activities involved in sucrose metabolism in grains The total soluble sugar content in grains of SN1391 increased but that of GC8901 and sucrose contents in grains of the two cultivars decreased after stressed at early filling stages. After the wheat was stressed at early and mid grain filling stages, the total soluble sugarcontent declined sharply and sucrose content increased in SN1391, but the changing trend of those in GC8901 was different according to the treatment manner. The total soluble sugar and sucrose contents in grains of GC8901 increased except that the sucrose contents of shading treatment were reduced. Three days after stessed at early filling stages, the activities of SS increased except those of high temperature and temperature with light interactant treatments of GC8901 decreased, and the activities of SPS declined. But the SS and SPS activities increased too except that the SS activities of shading stress and SPS activities of S2 of GC8901 decreased after stressed at early and mid grain filling stages. Compared the SS activity of SN1391 with that of GC8901, we found that the SS activity of grains in SN1391 with more starch was higher than that in GC8901 which has less starch under the natural condition but was lower under the high temperature stress and temperature with light interactant stress. The activities of AI and NI in grains of high temperature and temperature with light interactant stresses at early filling stages declined markedly and those of shading stress increased. Three days after stressed at early and mid filling stages, the AI activity decreased and NI activity increased except those of S2 of GC8901, which showed the opposite trent. Correlation analysis showed that there was a significant positive correlation between sucrose content and the activities of SS, SPS, AI and NI in grains, the simple relation coefficient of sucrose content to NI was maximal but that to SPS was minimal, only was 0.753. 2.4.3 Enzymes involved in starch synthesis The activities of ADPGPPase of the two cultivars declined shaply except that of J1 treatment and the UDPGPPase activities were all increased after stressed. The activities of SSS and GBSS were all reduced except that the SSS activity of S2 of SN1391 was slightly increased. After stressed at different filling stages, the SBE activities in grains decreased obviously except for those of T1 and J1 treatments of SN1391 and DBE activities increased except for J1 treatment of GC8901. Simple correlation analysis of total starch, amylose and amylopectin contents to the enzymes involved in starch synthesis during the whole filling stages showed that, except there... |
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