| In order to illustrate the reason for the thinness of CHA-based hybrids (chemical hybridizing agent), with Shannong18 and SN05-3 and their male sterile lines of CHA as materials, CHA BAU-9403 (1.00kg/hm2) was used during pistil and stamen period. The flag-leaf of the wheat was observed with electron microscope during grain filling stage. Big and small vascular bundle in the internodes under spikes and cob were determined. And changes on activities of sucrose in flag-leaf and starch in grain and related enzymes were studied. The results showed that:1. The number of starch grain in flag-leaf of CHA-based hybrids was higher than their fertile lines,and the volume of starch grain increased,too. The number of starch grain in flag-leaf of Shannong 18 and SN05-3 respectively increased 1.85/cell and 2.25/cell,and the volume respectively increased 2.11×105nm2 and 2.25×105nm2. It showed that the photosynthate accumulated in leaf of the male sterile lines with the form of starch..2.Dealed with BAU-9403, the number and area of the vascular bundle in the internodes under spikes and cob of the two wheat strains decreased significantly. The number of the big vascular bundle in the internodes under spikes of the two wheat strains decresed 1.6 and 1.4, and the area decreased 1193.10μm2 and 1925.85μm2; The number of the small vascular bundle in the internodes under spikes of the two wheat strains decresed 1.1 and 1.3, and the area decreased 345.95μm2 and 364.70μm2; The number of the vascular bundle in the cob of the two wheat strains decresed 2.4 and 2.3, and the area decreased 8043.45μm2 and 4404.53μm2; It showed that BAU-9403 had negative effect on vascular tissue of the stem and cob of wheat, and the transportat of the photosynthate in leaf of wheat was hinded.3.Activity of SPS in flag-leaf of the male sterile lines was higher than their fertile lines, which made sucrose and soluble sugar content in flag-leaf of the male sterile lines were lower than their fertile lines by 0.30~12.30mg·g-1 and 2.60~23.30mg·g-1, showing significant difference(T=-3.527~-4.106,Pr=0.045~0.0074). But sucrose and soluble sugar content in grain of the sterile lines were respectively 25.74~73.5mg·g-1 and 15.77~64.10mg·g-1 lower than the fertile lines(T=1.95~2.52, Pr=0.016~0.049). It showed that there were plenty of transportable assimilation in flag-leaf of the sterile lines,and BAU-9403 had negative effect on assimilation transport and effected supply of starch synthesis material.4.Changes on activities of SPS,SS,SSS and GBSS all exhibited single peak during grain filling. BAU-9403 made them be respectively 0.11~0.36s mg.grain-1. min-1,6.14~21.76 nmol.grain-1.min-1 and 0.31~11.59 nmol.grain-1.min-1 lower than their fertile lines,showing significant difference (T=4.103~6.115, Pr=0.0018~0.0074). Ability of starch synthesis decreased,and marerials of starch synthesis were not sufficient, which made quantity of starch synthesis decreased.5.There were different effects of BAU-9403 on SPS in flag-leaf and SS,SSS GBSS in grain with different genotype. BAU-9403 on SN05-3 was more sensitive than on Shannong 18.The increasing or decreasing range of the sterile lines of SN05-3 were 27.83%,7.04%,5.27% and 6.99% bigger than Shannong18,showing significant difference(T=-2.166~-4.875, Pr=0.004~0.048).Therefore, negative effect of BAU-9403 on vascular tissue of the stem and cob in wheat, photosynthate transport from source leaves, the activities of SS,SSS and GBSS and starch content in grain,was the significant factor that grain weight of CHA-based hybrids decreased. Choosing good CHA and wheat genotype with little bad effect on CHA was beneficial to improving the quality of hybrid seed production.
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