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Articles

Dependence of Nitrite Reduction on Electron Transport Chloroplasts ¹

^a Department of Agronomy, University of Illinois, Urbana, Illinois 61801

Methyl viologen and phenazine methosulfate (photosystem I electron acceptors), 3-(3,4-dichlorophenyl)-1, 1-dimethylurea (DCMU, electron-transport inhibitor), and methylamine (photophosphorylation uncoupler) were used to study the dependence of nitrite reduction on electron transport in chloroplasts.

DCMU, methyl viologen, and phenazine methosulfate markedly inhibited, whereas methylamine stimulated NO₂^– reduction in isolated, intact spinach (Spinacia oleracea L.) chloroplasts. The addition of DCMU to leaf sections of spinach and corn, (Zea mays L. var. XL81), incubated with No₃^–, caused no inhibition of nitrate reduction but inhibited nitrite reduction leading to the accumulation of NO₂^– in the light. The addition of methylamine to comparable leaf sections did not affect either nitrate or nitrite reduction.

We concluded that: (a) nitrite reduction is functionally associated with the electron transport arising from the light reactions of the chloroplast and this provides additional support for the localization of nitrite reductase in the chloroplast; (b) nitrite reduction is associated with photosystem I and ferredoxin is the most likely donor in leaf tissue; and (c) ATP is not involved directly in nitrite reduction. However, ATP synthesis, by regulating electron flow to photosystem I, can affect nitrite reduction in the light.

¹ This work was supported in part by Hatch funds and a Frasch Foundation Grant. C.A.N. gratefully acknowledges the assistance of a fellowship grant from Midwest Universities Consortium for International Aid. Universidad Agraria La Molina, Peru.