Kinetics of NO3- influx in spruce

Abstract

Influxes of 13NO3- across the root plasmalemma were measured in intact seedlings of Picea glauca (Moench) Voss. Three kinetically distinct uptake systems for NO3- were identified. In seedlings not previously exposed to external NO3-, a single Michaelis-Menten-type constitutive high-affinity transport system (CHATS) operated in a 2.5 to 500 μM range of external NO3- [NO3-]o. The Vmax of this system was 0.1 μmol g-1 h-1, and the Km was approximately 15 μM. Following exposure to NO3- for 3 d, this CHATS activity was increased approximately 3-fold, with no change of Km. In addition, a NO3--inducible high-affinity system became apparent with a Km of approximately 100 μM. The combined Vmax for the..