Role of reactive oxygen species in auxin herbicide phytotoxicity: current information and hormonal implications — are gibberellins, cytokinins, and polyamines involved?

Abstract

It has been suggested that reactive oxygen species (ROS) participate in the injury and death of sensitive plants treated with auxin herbicides. However, their precise role in the phytotoxicity of these compounds has not been completely elucidated. ROS might not only be essential for inducing epinasty, senescence, and tumours, but they might be crucial to the generation of ethylene, abscisic acid, and jasmonic acid, which are known to be triggered upon application of these compounds. Also, the main sources of ROS overproduction and their subcellular location in plants treated with auxin herbicides have not yet been clarified. Recent studies have suggested a role for xanthine oxidase (XOD) (which produces superoxide radical ([Formula: see text]) and has activity related to nucleic acid catabolism) and for peroxisomes in the oxidative stress and senescence induced by auxin herbicides in the leaves of sensitive plants. However, confirmatory studies at the molecular level are still needed, as well as studies on the possible involvement of other hormones, such as gibberellins, cytokinins, and polyamines, and their corresponding crosstalk with ROS, in the mode of action of auxin herbicides. The results from these studies could not only help to clarify the mechanism of phytotoxicity of these compounds, but also to enable the design of ecologically safer herbicides for agriculture.