Metabolic Characteristics Associated with Starch , Protein , and Oil Deposition in Developing Maize Kernels

The physiological processes that control relative starch, protein, and oil concentration of maize (Zea mays L.) kernels are not well defined. In this study, associations between metabolic characteristics of developing kernels and specific storage product accumulation in mature kernels were identified. In a field experiment, kernels of maize genotypes with widely divergent chemical composition were harvested 50 days post pollination (DPP) to compare starch, protein, and oil concentrations with enzyme activities, sugar, and amino acid levels of kernels harvested 20 DPP. Mature kernel starch concentrations were correlated with immature kernel sucrose concentrations and ADP-glucose pyrophosphorylase activities. Amino acid concentrations in immature kernels were correlated with the activities of phosphoglucoisomerase, phosphoglucomutase, pyrophosphate:fructose 6-phosphate I-phosphotransferase, and aldolase and with mature kernel protein concentrations, but negatively correlated with starch concentrations. Oil concentrations were positively correlated with mature embryo dry weights and with malate dehydrogenase activities in isolated embryos harvested 20 DPP. The results suggest a complex interaction of sugars and amino acids supplied to the kernel by the plant affecting enzyme activities and storage product accumulation in the developing kernel. High-starch genotypes supplied more sucrose to their kernels, had higher ADP-glucose pyrophosphorylase activity, and greater starch accumulation. High-protein genotypes supplied more amino acids to their kernels, and had enhanced expression of a number of enzymes that may contribute to the greater protein accumulation. These data suggest that nutrient supply interacts with expression of enzyme activities in developing kernels to determine starch and protein concentrations