| Wheat is one of the most important food crops in China.The superior grains in the first and second positions in the middle of the wheat ear grow early,are well-filled,and have a high grain weight,while the inferior grains in the third position and above grow late,are poorly filled,and have a low grain weight.This asynchronous phenomenon not only limits the potential for high yields but also seriously affects quality.Leaves are the main photosynthetic"source" organ of wheat,providing the main raw material for grain filling.Reducing the number of leaves can reduce the speed of "flow" and the development process of "storage"tissue to a certain extent.Exogenous spraying of ABA can reduce the photosynthetic efficiency of leaves to a certain extent.However,the mechanism of leaf cutting and exogenous spraying of ABA on the development of wheat grains at different ear positions is not clear.In this experiment,Yangmai 25 and Ningmai 13 were used as materials for leaf cutting treatment during the flowering period.Jimai 22 was used as material for exogenous spraying of ABA treatment during the earing period.The development process of wheat grains 10 days after flowering was observed by semi-thin sectioning technique.The effects of source reduction on the physicochemical properties of starch in different grain positions were analyzed by X-ray diffraction,Fourier transform far-infrared spectroscopy and other techniques.The results showed that:(1)With the decrease in the number of effective photosynthetic leaves,the spike length and grain number of Yangmai 25 and Ningmai 13 gradually decreased.The thousand-grain weight of superior grains in Yangmai 25 decreased by 12.27%,23.24%and 29.16%,while that of superior grains in Ningmai 13 decreased by 2.06%,6.76%and 13.69%The thousandgrain weight of inferior grains in Yangmai 25 decreased by 16.7%,25.28%and 33.56%,while that of inferior grains in Ningmai 13.(2)As the number of filling days gradually increases,the dry matter in the wheat caryopsis gradually increases and the moisture content gradually decreases.By observing the tissue sections of the caryopsis 10 days after flowering,the rate of pericarp disappearance and the accumulation rate of starch in the endosperm of superior grains were faster than those of inferior grains.After reducing the source,as the number of leaves cut increases,the speed of pericarp disappearance and the amount of starch accumulated in the endosperm gradually decrease,eventually leading to a decrease in the amount of dry matter accumulated in the grains.(3)As the number of leaves cut increases,the total starch content in superior and inferior grains gradually decreases.The apparent amylose content of superior grains in Yangmai 25 increased by 22.2%,27.25%,and 36.21%,while that of superior grains in Ningmai 13 increased by 5.74%,9.84%,and 13.99%.The apparent amylose content of inferior grains in Yangmai 25 decreased by 7.23%,12.7%,and 18.37%,while that of inferior grains in Ningmai 13 decreased by 3.85%,7.7%,and 12.02%.Leaf cutting treatment increased the solubility and expansion potential of superior and inferior grains in Yangmai 25,while the starch expansion potential of superior and inferior grains in Ningmai 13 decreased and solubility was not significantly affected.At the same time,leaf cutting treatment reduced the external orderliness of starch particles in superior and inferior grains of Yangmai 25 and Ningmai 13,reduced the relative crystallinity of starch in superior grains,and increased the relative crystallinity of starch in inferior grains.In addition,compared with the control group,leaf cutting treatment reduced the content of B-type starch granules in superior and inferior grains,narrowed the developmental differences between superior and inferior grains,and after cutting flag leaves,there was no significant difference in apparent amylose content between superior and inferior grains.(4)After exogenous spraying of ABA during earing period,wheat spike length shortened by 15.42%,thousand-grain weight of superior grains decreased by 7.21%,and thousand-grain weight of inferior grains increased by 2.75%.Exogenous spraying of ABA reduced B-type starch granule content(6.67%,4.05%),apparent amylose content(3.95%,8.22%),expansion potential(7.61%,9.05%)in superior and inferior grains respectively,solubility decreased by 3.93%for superior grains,total starch content increased by 6.02%for inferior grains.During wheat growth and development,after reducing "source" to a certain extent through leaf cutting or exogenous spraying of ABA,the accumulation amount of nutrients in grains reduced,which affected wheat yield and quality.At the same time,the higher the position and the more leaves are removed,the more significant the impact on grain development.Compared with superior grains,inferior grains are more easily affected.This study further deepens our understanding on mechanisms underlying developmental differences between different grain positions in wheat.This provides an effective approach and theoretical basis for improving wheat yield and quality. |
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