Comparative Study On Sucrose Metabolism And Transport In Zhengdan 958 And Xianyu 335 Grain Filling Stage

Zea mays is one of the most important cereal crops in the world, the yield of per plant is influenced by many factors, such as panicle weight, grain weight, kernel number per panicle, kernel rows per ear, silking period and water content etc. Among above factors, panicle weight, grain weight, kernel number per panicle and kernel rows per ear are major factors, which are related to sucrose transportation. Sucrose, as the main products of photosynthesis, is the main form of long-distance transportion and distribution in higher plants. In this study, Zhengdan 958 and Xianyu 335 are used as experimental materials, which are main cultivated varieties in Liaoning Province. Based on the significant difference in the grain filling between the two varieties, this paper compares key enzyme activity of sucrose metabolism in leaf and grain, analyses gene expression level of sucrose transporter, and then discusses the differences of the main reason of Zhengdan 958 and Xianyu 335 in the grain filling stage from the perspective of sucrose metabolism and transport, the above laying a theoretical foundation for the cultivation of Maize Varieties with high yield and quality.The main results are as follows:(1) Photosynthetic rates and chlorophyll contents of Xianyu 335 and Zhengdan 958 show a decreasing trend during grain filling in leaves, and the photosynthetic rate decreased along with the decreasing photosynthetic pigment content. The chlorophyll contents of the two varieties have no obvious difference, photosynthetic rate, lutein and carotenoid content of Xianyu 335 are significantly higher than those of Zhengdan 958 during the grain filling stage, the higher lutein and carotene contents are beneficial to maintain high photosynthetic capacity and efficiency in Xianyu 335,,which providing more material and energy for grain filling sufficiently. Xianyu 335 ended the grain filling in the 42 days after pollination, and Zhengdan 958 continued to 49 days.(2) During the grain filling stage, the content of sucrose, fructose and glucose of leaves in Zhengdan 958 are significantly higher than that of Xianyu 335, the starch content has the same change in 28-35 days after pollination. The SS activity of Xianyu 335 is significantly higher than that of Zhengdan 958, indicating the ability of decomposing sucrose strongly, at the same time the photoassimilate of accumulate in the source leaf is transported to sink organs rapidly, but that can not be transported timely in Zhengdan 958, part of the product in the form of starch storage in the leaves, which is not conducive to the grain filling. In 18-35 days after pollination, SPS activity of Zhengdan 958 is significantly higher than that of Xianyu 335, which consistent with the high level of sucrose content.(3) After 21 days of pollination, three kinds of soluble sugar content in grain of Zhengdan 958 and Xianyu 335 reach the maximum, and Zhengdan 958 is significantly higher than that of Xianyu 335. At this moment grain filling rate is also the largest value. The changes of sucrose content and cell wall invertase activity in grain are similar to the grain filling rate, which indicate the cell wall invertase affects the grain dry matter accumulation by adjusting the supply of sugar, and also affects the starch accumulation. At the late grain filling stage(35-42days after pollination), the starch content of grain in Xianyu 335 is significantly higher than that of Zhengdan 958, and the grain filling rate increased rapidly at the same time, which indicate the late grain filling stage is important period in the formation of grain yield of Xianyu 335 ,, and the higher filling rate and starch content are the most important factors in the formation of grain yield at this stage.(4) The ZmSUTs gene expression level in leaves is different between Zhengdan 958 and Xianyu 335 during grain filling. And different members of sucrose transport gene family in maize play different roles. ZmSUTl is the main effect genes, whose expression level of two varieties in leaves during the grain filling stage show increased first and then decreased. The expression level of ZmSUT1 in Xianyu 335 increased more significantly than that of Zhengdan 958, a strong sucrose loading capacity of Xianyu 335 in the phloem of source leaves. And the ZmSUT1 in Zhengdan 958 is highly expressed in a long duration, which may be related to the longer grain filling period. The expression level of ZmSUT4 is regulated by the sucrose content in leaves, which illustrates it is relate to the sucrose transport during grain filling.In summary, compared with Xianyu 335, there is more soluble carbohydrate retention in leaves of Zhengdan 958 during late grain filling stage, the loading and exporting of photoassimilatethe in "source" are slowly, so the photoassimilate in "source" is not completely transported to the sink. The rate of starch synthesis in grain "sink" of Zhengdan 958 is slower, and grain filling rate has the same changs during later grain filling, but photosynthesis duration of Zhengdan 958 is longer, providing enough photoassimilate for grain filling, and the final dry weight and volume of grain show bigger. The supplying efficiency of "source" is higher of Xianyu 335, and the photosynthetic rate is significantly higher than that of Zhengdan 958 in the main period of grain filling. The gene expression level of ZmSUT1, which is responsible for sucrose transport in maize, is enhanced in Xianyu 335, and the photosynthetic product is able to transfer to grain timely, so the grain filling rate is faster.