Effects of ametryn [2-(ethylamino)-4-(isopropylamino)-6-(methylthio)-s-triazine] on nitrate reductase activity and nitrite content of wheat (Triticum aestivum L.)

The objectives of this study were to show that: (a) a herbicide, such as ametryn, which interferes with the photosynthetic electron transport system, causes nitrite to accumulate in illuminated leaves and (b) that nitrite is toxic and contributes to the herbicidal damage and death of the plant. Tests were conducted on wheat seedlings grown on 5 mM nitrate, 5 mM ammonia, and zero nitrogen. Ametryn treatment decreased in vivo and in vitro nitrate reductase activity (NRA) within a 26-hr period. In vivo NRA decreased more rapidly than in vitro NRA. Compared with control tissue, only 3% in vivo NRA remained at the end of 26 hr. The in vivo assay conducted in light confirmed the inhibition of photosynthetic electron flow by ametryn within the leaf tissue. Nitrate-grown, ametryn-treated plants accumulated nitrite and, after 10 days were the only plants that were completely desiccated and dead. Ammonia- and zero-nitrogen, ametryn-treated plants did not accumulate nitrite, were only partially chlorotic after the 10-day period, and were still living. Low levels of NO_(X) (NO₂ and/or NO) emissions were demonstrated by nitrate-grown ametryn-treated plants.