中文摘要：

对玉米果穗上部和中部籽粒发育前期的生理生化指标进行了比较研究，并采用“种子杯”技术研究了籽粒小穗柄卸载情况。结果显示，中部籽粒的发育情况明显优于上部；与上部籽粒相比，中部籽粒早期可溶性糖浓度高、后期淀粉累积快；中部籽粒和小穗柄中酸性蔗糖转化酶（SAI）活性均高于上部。对比不同时期小穗柄端的可溶性糖卸载量也是中部高于上部。研究认为，上部籽粒的发育不良不仅受制于库活性的不足，小穗柄端同化物卸载的不足也是一重要原因。

英文摘要：

Comparative studies were conducted on physiological and biochemical characters of maize kernels on both middle and upper part of ears during the early stage of kernel development, and ＂empty seed cup＂ technique was also used to study assimilates unloading from pedicel of kernels. The result showed that the development of middle kernels was better than that of upper kernels ; compared with the upper kernels, the middle kernels had higher concentration of soluble sugar at early stage and starch at late stage; Soluble Acid Invertase（SAI）activity in both kernel and pedicel of middle ear were higher titan that of upper part. The content of soluble sugar unloading from pedicel of middle pedicels was higher than upper part. It could be concluded that the underdevelopment of upper kernels might due to low sink activity and also low assimilates unloading from pedicels.