A Mode of Action of Herbicides: Inhibition of the Normal Process of Nitrite Reduction

Herbicides were shown to interfere in the normal process of enzymatic nitrite reduction by the plant in photosynthetic and nonphotosynthetic plant tissues with little effect on nitrate reduction. This preferential inhibition caused nitrite to accumulate. The occurrence of free nitrite within the plant can help to explain the toxicity symptoms, nastic growth reactions, abnormal metabolism and rapid death due to herbicide action. This blockage of nitrite reduction was shown with all photosynthetic inhibitor herbicides tested and with numerous other herbicides. The effect was demonstrated using an in vivo assay, intact green plants and germinating seedlings. A basic in vivo method was presented which can provide rapid screening tests for photosynthetic inhibitor herbicides, a measure of herbicide specificity and surfactant specificity