Effects of Certain Herbicides and Their Combinations on Nitrate and Nitrite Reduction

A study was made concerning the effect of various herbicides, when used alone or in combination, on nitrite accumulation in excised leaves of wheat (Triticum aestivum L., var. ;Centurk'). Treatment of leaves with photosynthetic inhibitor herbicides, known to interfere with the transfer of light energy, caused accumulation of nitrite under illuminated, aerobic conditions. When certain other herbicides, which do not interfere with the photosynthetic process, were applied to leaves and incubated under dark, aerobic conditions, nitrite accumulations were enhanced over those treated with photosynthetic inhibitors or the controls. The combination of photosynthetic inhibitor herbicides and certain other "nonphotosynthetic inhibitor" herbicides caused relatively large amounts of nitrite to accumulate in light or in darkness. Nitrite accumulation occurs when nitrate and nitrite reduction are not in balance. The proposed actions of the herbicides used in this study are discussed. This discussion provides a rationale for the accumulation of nitrite by the herbicide-treated leaves.