Localization of nucleoside diphosphatase in the onion root tip

Summary Nucleoside diphosphatase activity occurs in the Golgi apparatus, on the plasmalemma, between the plasmalemma and the definitive cell wall, and in the endoplasmic reticulum of the onion root tip. The presence and/or relative concentrations of reaction product at each of these cellular sites occur in distinctive developmental patterns within the root. Cells with high NDPase activity at any combination of these sites also produce large amounts of a polysaccharide-rich product. A vacuolar activity also occurs in the pericycle and cortex in a developmentally distinctive pattern, but its location has not been correlated to polysaccharide secretory activity.