Role of ATP in nitrite reduction in roots of wheat and pea

Excised wheat (Triticum aestivum L.) and field pea (Pisum arvense L.) roots, incubated under anaerobic conditions or in the presence of uncouplers of oxidative phosphorylation [2,4-dinitrophenol (DNP), carbonylcyanide-m-chlorophenylhydrazone, pentachlorophenol] accumulated nitrite as a result of an inhibition of nitrite reduction. In isolated root plastids, nitrite reduction was dependent on a supply of glucose-6-phosphate (G6P) and did not require ATP. The estimated Km value for glucose 6-phosphate was 1.25 mM. Glucose and fructose-1,6-diphosphate were ineffective substrates for nitrate reduction. Anaerobic conditions and treatment with DNP, which would result in a cessation of ATP production by the mitochondria and a stimulation of glycolysis via the "Pasteur effect", were shown to decrease the G6P content of excised roots of wheat and pea. A negative correlation was observed between the level of G6P and nitrite accumulation on root tissues. It is proposed that an interruption in the supply of G6P to the root plastid under these conditions would result in an inhibition of nitrite reduction leading to nitrite accumulation.