Changes in Carbohydrate Accumulation and Activities of Enzymes Involved in Starch Synthesis in Maize Kernels at Different Positions on an Ear during Grain Filling

Abstract

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,sucrose and starch and the activities of the adenosine diphosphoglucose pyrophosphorylase(AGPase),starch synthase(St S),and starch branching enzyme(SBE) in kernels at different positions on an ear and their relationships with grain filling rate were determined. 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,St S,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,St S,and SBE in kernels. The results suggested that a smaller starch accumulation rate and lower weight for the kernels at the upper position on a maize ear are mainly attributed to lower activities of the enzymes involved in starch synthesis in these kernels. A higher kernel weight for the spring maize is closely associated with its stronger ability of starch synthesis in the kernels.