Effect of nitrogen supply on expression of some genes controlling storage proteins and carbohydrate synthesis in cultured maize kernels

Maize kernels (Zea mays L., inbred W64A) were cultured in vitro with a 200 mM sucrose concentration and either 0, 3.6, 7.1, 14.3, or 36.5 mM N, supplied as amino acids, in the culture medium. Increased N supply up to 14.3 mM N resulted in increased kernel dry weight and starch content. Increasing N supply increased storage protein 3-fold, which was reflected by 7-fold enhancement of alpha-zein message abundance. beta-Zein message abundance was not affected by N nutrition. Messages for the regulatory gene, Opaque-2, were doubled by the increased N supply. Messages for the Shrunken, Waxy, and Aldolase genes increased about 2-fold with increased N supply. Activities of sucrose synthase (encoded by Shrunken), and aldolase enzymes exhibited increases with N supply corresponding with that of their transcript abundance. Expression of the Shrunken-2 and Brittle-2 genes were not affected by N supply. It is likely that the increased expression of genes involved in carbohydrate metabolism is responsible for the increased capacity of a kernel to utilize available sucrose at higher levels of N nutrition.