大豆在南方地区广泛与高秆作物套作，苗期遭受荫蔽胁迫。叶片性状决定了光能截获与光能转化，与耐荫性密切相关。明确套作大豆苗期叶片的耐荫机理对提高荫蔽下的光能利用至关重要。我们前期研究发现：套作荫蔽下大豆叶片变小变薄，且大量差异表达基因参与了响应生长素刺激。因此申请者假设荫蔽胁迫改变了大豆叶片生长过程中的生长素含量，进而调控了细胞增殖与（或）细胞扩展，最终抑制了叶片扩张生长。为验证这一假设，本研究拟以不同小叶面积大豆品种为材料，综合利用植物生理、细胞生物、作物栽培等学科研究手段，设置不同光照和外源生长素调控处理，着重从叶片生长素合成量和极性运输、细胞周期、质膜H+泵活力、扩展蛋白基因表达等角度开展分析，明确荫蔽对大豆苗期叶片生长素含量、细胞增殖和细胞扩展的影响，以及叶片细胞增殖与细胞扩展对外源生长素调控的响应，阐明生长素调控大豆苗期叶片生长的生理机制，为套作大豆苗期生长调控提供理论基础。

Soybean is widely relay-intercropped with taller crops in southern China, the seedling of soybean often grew under shade stress in relay intercropping. Leaf traits are closely associated with shade tolerance, as the leaf area determines light interception and photosynthesis in leaf mesophyll determines light conversion. It is important to know mechanism of shade tolerance in laminar of soybean seedling for improving light use utilization in shade in relay intercropping system. Our previous studies found that soybean laminar became smaller and thinner when grew under shade in relay intercropping, and many differentially expressed genes involved in responses to stimulus of auxin. Therefore, we hypothesized that the auxin was induced by shade in soybean laminar, and further regulated the cell proliferation and cell expansion, finally inhibited the leaf expansion growth. To validate the hypothesis, we plan to use inter-disciplinary researching methods by setting different light environment and exogenous auxin treatments on two soybean cultivars with different leaflet area. We proposed to emphatically analyze the production and polar transporation of endogenous auxin, cell cycle, plasma membrane H+-ATPase activity, and EXPANSIN expression level in laminar of soybean seedling under shade. The results could confirm the effects of shade on auxin content, cell proliferation and cell expansion, and the responses of cell proliferation and cell expansion to application of exogenous auxin and inhibitor of auxin polar transport in soybean laminar, so as to explore the regulatory mechanism of auxin on laminar expansion growth in soybean seedling. This study will provide a theoretical support for regulations on growth of soybean seedlings in relay intercropping system.