Protoporphyrin IX Accumulation in Lemna paucicostata Hegelm. Caused by Diphenyl Ether Herbicides and Their Herbicidal Activity.

Abstract

The relationship between protoporphyrin IX (Proto IX) levels and herbicidal activity of diphenyl ether herbicides in intact higher plant Lemna paucicostata Hegelm. strain 441 was determined. Rapid accumulation of Proto IX in the plant was observed after simultaneous exposure to light and oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl) benzene]. At 4hr, the accumulation reached the maximum and this was followed by a rapid decrease. The rate of decrease was slowed when the plants were transferred to darkness after 4hr light irradiation, although some Proto IX degradation continued in the dark. This suggests that not only photo-decomposition but degradation and/or metabolism which occurred in darkness are involved in the decrease. Proto IX levels accumulated in the plants and electrolyte leakage from the plants were increased with increasing concentration of oxyfluorfen. A positive correlation was found between Proto IX content and electrolyte leakage. Diphenyl ether herbicides used in the study had differential activity in the accumulation of Proto IX. A positive correlation was also found between Proto IX levels and their herbicidal activity to the plant.These data suggest that Proto IX is the principal compound responsible for the rapid electrolyte leakage from plants, and that variation in the herbicidal activity of the diphenyl ethers observed in the study is caused by differential activity in accumulation of Proto IX.