水稻幼穗分化期高温导致粒重严重下降，其内在机理不清。水稻粒重形成需要碳同化物作为物质基础，同时受植物激素调控：(i)幼穗分化期合成的碳同化物部分维持谷壳生长，部分以非结构性碳水化合物（NSC）储存于茎鞘并于抽穗后转运至谷粒；(ii)植物激素既调控小穗细胞增殖而影响谷壳生长，又调控叶片生长和维管束形态而影响NSC积累与转运，最终影响谷壳大小和谷粒充实，申请人前期研究发现幼穗分化期高温下幼穗细胞分裂素（CTK）变化与粒重变化的关系最密切。本项目以不同耐高温水稻品种为试验材料，于幼穗分化期进行对照和高温处理，研究茎鞘NSC积累与转运、幼穗CTK积累（根源CTK运输、幼穗CTK合成与降解）对高温的响应及其与粒重形成的关系，并设置外源CTK分别施用于幼穗和根系验证幼穗CTK和根源CTK运输对粒重形成的调控作用，从碳同化物供应和CTK调控方面揭示幼穗分化期高温影响水稻粒重的原因和生理机理。

Heat stress induced serious reductions in rice grain weight, but the underlying mechanisms are not clear. The accumulation and translocation of non-structure carbohydrate and phytohormone are important to husk size and grain plumpness.（i）non-structure carbohydrate supply not only maintains enlargement of spikelets, but also are stored in culm in the form of non-structural carbohydrates (NSC), which are transported to grain after heading; （ii）phytohormones regulate cell proliferation and affect spikelet enlargement, and regulate leaf growth and vascular bundle morphology and affect accumulation and transport of NSC, thus determines spikelet growth and grain filling. In our previous study, change in cytokinin (CTK) was most closely correlated with change in grain weight induced by heat during panicle initiation. In the present research, rice varieties of different heat tolerance are used, control and high temperature treatments are imposed during panicle initiation. We will study the response of accumulation and transport of NSC, CTK accumulation (transport of root-synthesized CTKs, local CTK synthesis and local CTK catabolism of the young panicle) to high temperature treatment, and theirs relationship with grain weight formation. Exogenous CTKs are applied to the young panicles and roots, respectively, to test the regulatory role of CTK content and root-synthesized CTKs transport on grain weight formation. The aim of this project intends to reveal the physiological mechanism of reduction in rice grain weight induced by heat during panicle initiation from the perspective of supply of carbon assimilate and CTK regulation.