Ioxynil (CAS 1689-83-4)

Ioxynil, a post-emergent herbicide, serves as an effective means of selectively controlling broad-leaved weeds in cereals and grass crops. To combat hormone-resistant weeds, it can be utilized in combination with phenoxy herbicides. This compound, known as a nitrile with a hydroxy group at position 4 and iodo groups at positions 3 and 5 of benzonitrile, boasts a diverse range of roles, including functioning as a xenobiotic, an environmental contaminant, and a herbicide. Its potent activity as a nitrile and iodophenol leads to its ability to act as an uncoupler of oxidative phosphorylation in plants and animals, and as an inhibitor of photoreduction and photophosphorylation reactions in chloroplasts. Additionally, higher concentrations of ioxynil inhibit electron transport in isolated mitochondria and chloroplasts, ultimately leading to a rapid and severe alteration in the energy balance of plant cells. For instance, excised soybean hypocotyls treated with high concentrations of ioxynil experience a drastic reduction of ATP levels by up to 90% after three hours of treatment. Studies examining the hormonal control of proteolytic and amylolytic enzyme activity in germinating seeds indicate that ioxynil may interfere with the development or transport of cytokinin and gibberellin hormones, or hinder the biosynthetic processes involved in enzyme formation. As for its mechanism of action, ioxynil inhibits the second light reaction of photosynthesis. Notably, it also obstructs the energy-dependent uptake of Ca(2)+ in plant mitochondria (such as maize and zucchini) without interfering with ADP phosphorylation or tubulin polymerization. A common mode of action for ioxynil possibly involves inhibiting the regulation of cytoplasmic free Ca(2)+ concentration, resulting in various physiological malfunctions.