Glufosinate enhances the activity of protoporphyrinogen oxidase inhibitors

Abstract

Glufosinate inhibits glutamine synthetase (GS), a key enzyme for amino acid metabolism and photorespiration. Protoporphyrinogen oxidase (PPO) inhibitors block chlorophyll biosynthesis and cause protoporphyrin accumulation, a highly photodynamic intermediate. Both herbicides ultimately lead to plant death by a massive accumulation of reactive oxygen species (ROS) through different mechanisms. We investigated a potential synergistic effect by the mixture of the two herbicide mechanisms of action (MoAs). The tank mix between a low rate of glufosinate (280 g ai ha−1) with an ultra-low dose of saflufenacil (1 g ha−1) provided enhanced herbicidal activity compared with the products applied individually on Palmer amaranth (Amaranthus palmeri S. Watson). The synergism between the two herbicides was also confirmed by isobole analysis and field trials. The herbicide combination provided high levels of efficacy when applied at low temperature and low humidity. Mechanistically, glufosinate caused a transient accumulation of glutamate, the building block for chlorophyll biosynthesis. Consequently, inhibition of both GS and PPO resulted in greater accumulation of protoporphyrin and ROS, forming the physiological basis for the synergism between glufosinate and PPO inhibitors. While the synergy between the two herbicide MoAs provided excellent efficacy on weeds, it caused low injury to PPO-resistant waterhemp [Amaranthus tuberculatus (Moq.) Sauer] and high injury to both glufosinate-resistant and glufosinate-susceptible soybean [Glycine max (L.) Merr.]. Glufosinate enhances the activity of PPO inhibitors through glutamate and protoporphyrin accumulation, leading to increased levels of ROS and lipid peroxidation. The synergism between the two herbicide MoAs can help to overcome environmental effects limiting the efficacy of glufosinate. Future research is needed to optimize the uses for this herbicidal composition across different cropping systems.

Glufosinate‐ammonium: a review of the current state of knowledge

“…2 The tank mix of PPO-inhibitors and glufosinate provides enhanced herbicidal activity compared to the products applied individually. 86 The synergistic effect originates from the inhibition of GS by glufosinate leading to a transient accumulation of glutamate, the precursor for chlorophyll biosynthesis in plants. Inhibition of chlorophyll biosynthesis by PPO-inhibitors causes accumulation of protoporphyrin IX, which is enhanced by the accumulation of glutamate in the presence of glufosinate.…”

“…The herbicide combination also provided improved weed control in the field, and may help to overcome negative effects of environmental conditions on glufosinate performance. 86 While this combination has potential to be widely adopted, the effect seems to vary across species, doses, and PPO chemistry. Thus, more research is needed to identify the best combination for each particular situation to maximize the synergistic effect on weed control.…”

“…Herbicides targeting PPO cause protoporphyrin IX accumulation, which is a photodynamic compound that leads to ROS generation 2 . The tank mix of PPO‐inhibitors and glufosinate provides enhanced herbicidal activity compared to the products applied individually 86 . The synergistic effect originates from the inhibition of GS by glufosinate leading to a transient accumulation of glutamate, the precursor for chlorophyll biosynthesis in plants.…”

“…Thus, the synergism observed with the mixture between glufosinate and PPO‐inhibitors results from protoporphyrin IX accumulation to higher levels when both GS and PPO are inhibited simultaneously. The herbicide combination also provided improved weed control in the field, and may help to overcome negative effects of environmental conditions on glufosinate performance 86 . While this combination has potential to be widely adopted, the effect seems to vary across species, doses, and PPO chemistry.…”

A systematic approach for finding herbicide synergies

“…Synergy is desirable when designing a herbicide mixture as it allows lower application rate or frequency of herbicide treatment, but finding a new synergy remains challenging. Sometimes, synergy can be hypothesised based on mechanistic assumptions, as it was done by Takano et al 7 who predicted the synergy between glufosinate and protoporphyrinogen oxidase inhibitors and confirmed it experimentally, but generally synergies are not predictable. Despite frequent claims of synergy in patent literature, the number of peer-reviewed publications describing synergistic herbicide combinations is relatively low.…”