Metabolic phenotype of heterosis in Zea mays

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Maize is an important crop and a model system for heterosis. Heterosis was established for two widely used elite maize inbred lines, B73 and Mo17. These lines will used here to study the effects of heterosis on starch biosynthesis in the maize seed. Metabolite flux leading to the incorporation of glucose units into starch of the endosperm will be analysed by retrobiosynthetic NMR spectroscopy. The 'recycling' of glucose prior to incorporation into starch via glycolysis, glucogenesis and the pentose phosphate pathway will be quantitatively determined by this method. Developing maize kernels are labelled with mixture of [U-13C6]glucose and unlabelled glucose. After labelling starch is hydrolyzed and isotopomer composition of the resulting glucose is determined by quantitative NMR the "metabolic history" of the glucose units can be reconstructed from these data. The comparison of inbred and hybrid kernels will yield information on whether the increase of starch is based on qualitative or quantitative changes in metabolite flux. The determination of the isotopomer composition of soluble carbohydrates will provide additional information.