Effects of nitrite, chlorate, and chlorite on nitrate uptake and nitrate reductase activity.

Effects of NO(2) (-), ClO(3) (-), and ClO(2) (-) on the induction of nitrate transport and nitrate reductase activity (NRA) as well as their effects on NO(3) (-) influx into roots of intact barley (Hordeum vulgare cv Klondike) seedlings were investigated. A 24-h pretreatment with 0.1 mol m(-3) NO(2) (-) fully induced NO(3) (-) transport but failed to induce NRA. Similar pretreatments with ClO(3) (-) and ClO(2) (-) induced neither NO(3) (-) transport nor NRA. Net ClO(3) (-) uptake was induced by NO(3) (-) but not by ClO(3) (-) itself, indicating that NO(3) (-) and ClO(3) (-) transport occur via the NO(3) (-) carrier. At the uptake step, NO(2) (-) and ClO(2) (-) strongly inhibited NO(3) (-) influx; the former exhibited classical competitive kinetics, whereas the latter exhibited complex mixed-type kinetics. ClO(3) (-) proved to be a weak inhibitor of NO(3) (-) influx (K(i) = 16 mol m(-3)) in a noncompetitive manner. The implications of these findings are discussed in the context of the suitability of these NO(3) (-) analogs as screening agents for the isolation of mutants defective in NO(3) (-) transport.