Distribution of enzyme activities within the developing maize (Zea mays) kernel in relation to starch, oil and protein accumulation

Abstract

The association of enzyme activities in developing kernels with specific storage product accumulation at maturity was analyzed in different parts of Zea mays inbred OH43 kernels. Maize kernels were harvested at 20 and 55 days post‐pollination and dissected into basal region, pericarp, embryo, lower endosperm, middle endosperm and upper endosperm. Mature (55 days pos(‐pollination) kernel parts were analyzed for starch, total protein, zein and oil content. Immature (20 days post‐pollination) kernel parts were assayed for activities of 15 enzymes of sugar and amino acid metabolism. Statistical analyses of the data suggested that glucokinase (EC 2.7.1.2) fructokinase (EC 2.7.1.4) and phosphofructokinase (EC 2.7.1.1 11) activities were primarily associated with oil accumulation, whereas ADP′‐glueose pyrophosphorylasc (EC 2.7.7.27) and sucrose synthase (EC 2.4.1.13) activities were associated with starch accumulation. The results suggest that oil biosynthesis utilizes inveitase‐mediated sucrose degradation in a pathway not requiring pyrophosphatc. whereas starch biosynthesis utilizes a sucrose synthase‐mediated pathway of sucrose degradation in a pathway requiring pyrophosphatc. Additional groups of enzyme activities were associated with each oilier but not with any specific storage product and appeared to be associated with general metabolic activity.