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 co ntent. 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 t he Shrunken-2 and Brittle-2 genes were not affected by N supply. It is likely that the increased expression of genes involved in carbohydrat e metabolism is responsible for the increased capacity of a kernel to utilize available sucrose at higher levels of N nutrition.