The Effect Of 24-epibrassinolide(EBR) Application At Panicle Initiation Stage On The Panicles Development And Grain Fillingof Rice

The production of rice is highly related to the capacity of grain filling, which is strongly affected by source and sink. It has been reported by myriads of research that Brassinosteroids(BRs) have positive influence on rice growth, development and yield. To further explore the mechanism that BRs modulate the relationships among source strength, sink size and sink activity, Nipponbare was used as materials under filed condition. Through treating rice leaves of panicle initiation stage with 24-epibrassinolid(EBR), a series of index were analyzed, which includes non-structure carbohydrate(NSC) accumulation in leaves, stem and sheath during flowering stage; the metabolism, transportation and assimilation of NSC. Combined with the data of growth, development and grain filling, we further study the influence of the treatment on the panicle development and grain filling and thus the mechanism behinds them.(1) Foliar spraying with EBR during panicle initiation stage promotes the development of panicles and grains. In addition, different EBR concentration has different effect on grain: T1(0.2 μmol/L) treatment can significantly increase the grain size, while had no significant effect on the development of panicle; Compared with T0 treatment, T2(1 μmol/L) treatment promotes the development of panicles by increasing the length, weight, primary rachis branch number, secondary rachis branch number, grain number of panicles and the grain density by 8.3%, 20%, 10.6%, 23.4%, 16.6% and 7.3% respectively. Moreover, T2 treatment also increased the size of both superior and inferior grains. Affected by panicle development, foliar spraying with different concentration of EBR during panicle initiation stage lead to different influence: T1 treatment increases the grain weight by 6.7% while shows no effect on grain number; T2 treatment significantly increases grains number per square meter while shows slight effect on the grain weight. Therefore, two EBR treatments with different concentrations increased the sink size by different way.(2) Foliar spraying with EBR during panicle initiation stage can significantly increase the plant height of 10-25 d after treatment, the rice leaf area, leaf angle and leaf chlorophyll content during filling stage. Both EBR treatments can increase the aboveground biomass and the NSC content in vegetative organs at the flowering stage, improve the sucrose phosphate synthase(SPS) activity and sucrose content in leaves during grain-filling stage. Therefore, EBR treatments can improve the source strength of rice by increasing the biomass storage before grain filling stage and transportation of carbon assimilates.(3) Foliar spraying with varies concentration of EBR at panicle initiation stage promotes the sucrose lyase activity of grain, enhanced the transportation of NSC from vegetative organs to grains and increase starch accumulation of grain. EBR treatments enhances the sucrose lyase activity in both superior grains and inferior grains, especially the acid invertase(AI) activity in inferior grains. The improvement of AI activity in inferior grains accelerated the transportation of assimilates to inferior grains and thus the synthesizing activity of starch. Moreover, the increasing content of NSC and starch in inferior grains is beneficial to the grain plumpness of inferior grains, which further increase seed setting rate.(4) Although both EBR treatments significantly improve the sink size and source activity, the treatment-caused change of source capacity varies. Low concentration of EBR leads to slight increasing of source capacity, which limits the utilization of photosynthesis products and increases the content of NSC in vegetable organ during harvest stage due to the storage of un-used photosynthesis products. However, compared to low concentration of EBR, high concentration of EBR treatment lead to a higher increase of source capacity, which further enhances photosynthesis products transportation during grain filling stage and thus increases the efficiency of grain filling through decreasing the content of NSC in vegetable organs.In conclusion, the grain filling of rice was influenced by source strength, sink size and sink activity. In our study, the improved source capacity and sink activity are the preconditions for the increased grain yield, and the sink size modulated by EBR treatments ultimately determined the final yield. Two EBR treatments with different concentration significantly increased rice yield by 5.6% and 15.2% respectively. Compared with T1, T2 treatment has an increasing yield of 9.1%. Therefore, the increase of grain number is more important than grain weight for the yield of rice.