中文摘要：

玉米果穗顶部籽粒通常较中、下部籽粒充实差,粒重轻,其机制不清楚。本研究旨在探明玉米果穗不同部位籽粒淀粉合成相关酶活性变化及其与籽粒灌浆的关系。以玉米品种登海11为材料,分别进行春播和夏播试验,观察果穗不同部位籽粒中可溶性糖、蔗糖和淀粉的含量及淀粉合成相关酶活性变化。结果显示,与夏播玉米相比,春播玉米具有较多的每穗粒数、较高的百粒重和产量。虽然产量在春播和夏播间有差异,但两季玉米籽粒的最大灌浆速率、平均灌浆速率、百粒重、可溶性糖和蔗糖含量、最大淀粉积累速率、平均淀粉积累速率均表现为果穗下部籽粒〉中部籽粒〉上部籽粒。灌浆期果穗不同部位籽粒腺苷二磷酸葡萄糖焦磷酸化酶（AGPase）、淀粉合酶（St S）和淀粉分支酶（SBE）活性变化均呈单峰曲线,果穗上部籽粒AGPase、St S和SBE活性峰值和平均值均显著低于果穗中、下部籽粒。相关分析表明,淀粉积累速率、籽粒灌浆速率与AGPase、St S和SBE活性均呈极显著正相关。说明玉米果穗顶部籽粒较低的AGPase、St S和SBE活性是其灌浆较差、粒重较低的重要原因。春播玉米粒重较高,与其灌浆期较强的淀粉合成能力有关。

英文摘要：

Kernels at the upper position of a maize ear usually show slower filling rate and lower weight than those at the basal and middle positions. The mechanism is little understood. The objective of this study was to understand if changes in carbohydrate accumulation and activities of the enzymes involved in starch synthesis in the kernels at different positions on a maize ear were associated with grain filling. A maize cultivar Denghai 11 was planted in spring and summer. Contents of the soluble sugar, su-crose and starch and the activities of the adenosine diphosphoglucose pyrophosphorylase （AGPase）, starch synthase （StS）, and starch branching enzyme （SBE） in kernels at different positions on an ear and their relationships with grain filling rate were de-termined. The results showed that kernel number per ear, 100-kernel weight, and grain yield were more or higher for the spring maize than for the summer maize. Although the grain yield was different between the spring maize and the summer maize, the maximum kernel filling rate, mean kernel filling rate, 100-kernel weight, the contents of both soluble sugar and sucrose in kernels, the maximum starch accumulation rate and mean starch accumulation rate in kernels all exhibited an order of basal position 〉middle position〉 upper position. The activities of AGPase, StS, and SBE in kernels at different positions on an ear showed the changes of single peak curves, and the peak and mean enzymatic activities in kernels at the upper position were significantly lower than those at both middle and basal positions. The starch accumulation rate and kernel filling rate were very significantly and positively correlated with activities of AGPase, StS, and SBE in kernels. The results suggested that a smaller starch accumula-tion rate and lower weight for the kernels at the upper position on a maize ear are mainly attributed to lower activities of the en-zymes involved in starch synthesis in these kernels. A higher kernel weight for the spring maize is closely associate