Physiological basis for isoxadifen-ethyl induction of nicosulfuron detoxification in maize hybrids

Abstract

Isoxadifen-ethyl can effectively alleviate nicosulfuron injury in the maize. However, the effects of safener isoxadifen-ethyl on detoxifying enzymes in maize is unknown. The individual and combined effects of the sulfonylurea herbicide nicosulfuron and the safener isoxadifen-ethyl on the growth and selected physiological processes of maize were evaluated. Bioassays showed that the EC50 values of nicosulfuron and nicosulfuron plus isoxadifen-ethyl for maize cultivar Zhengdan958 were 18.87 and 249.28 mg kg-1, respectively, and were 24.8 and 275.51 mg kg-1, respectively, for Zhenghuangnuo No. 2 cultivar. Evaluations of the target enzyme of acetolactate synthase showed that the I50 values of nicosulfuron and nicosulfuron plus isoxadifen-ethyl for the ALS of Zhengdan958 were 15.46 and 28.56 μmol L-1, respectively, and were 0.57 and 2.17 μmol L-1, respectively, for the acetolactate synthase of Zhenghuangnuo No. 2. The safener isoxadifen-ethyl significantly enhanced tolerance of maize to nicosulfuron. The enhanced tolerance of maize to nicosulfuron in the presence of the safener, coupled with the enhanced injury observed in the presence of piperonyl butoxide, 1-aminobenzotriazole, and malathion, suggested cytochrome P450 monooxygenases may be involved in metabolism of nicosulfuron. We proposed that isoxadifen-ethyl increases plant metabolism of nicosulfuron through non-P450-catalyzed routes or through P450 monooxygenases not inhibited by piperonyl butoxide, 1-aminobenzotriazole, and malathion. Isoxadifen-ethyl, at a rate of 33 mg kg-1, completely reversed the effects of all doses (37.5–300 mg kg-1) of nicosulfuron on both of the maize cultivars. When the two compounds were given simultaneously, isoxadifen-ethyl enhanced activity of glutathione S-transferases (GSTs) and acetolactate synthase activity in maize. The free acid 4,5-dihydro-5,5-diphenyl-1,2-oxazole-3-carboxylic was equally effective at inducing GSTs as the parent ester and appeared to be the active safener. GST induction in the maize Zhenghuangnuo No. 2 was faster than in Zhengdan 958.

Response of maize (Zea maysL) inbred lines to different herbicide combinations

“…No phytotoxicity symptoms were observed in hand hoeing since inbred lines expressed fully their genetic potential in the absence of herbicide. Tolerant inbred lines CML312, CML444, CZL00001 had the lowest phytotoxicity score; this might have been a contribution of good genetic makeup and the ability to degrade these herbicides into less toxic form (Sun et al, 2017). Susceptible inbred lines CML488, CZL03014, L917 and N3.2.3.3 developed injury symptoms in response to metolachlor injury; they exhibited stunted shoots and leaf crinkling.…”

“…The response of maize inbred lines to various active agents depended on their genetic background (Stefanovic et al, 2000). Previous studies indicate that maize can metabolise nicosulfuron into harmless compounds by converting the parent herbicide to non phytotoxic-OH metabolite (Sun et al, 2017).…”

The Use of Herbicide Safener Increases the Selectivity of Nicosulfuron to Maize Crops

“…The biomass yield of sweet maize plants of tolerant lines and hybrids treated with malathion followed by foramsulfuron decreased 35% and 50%, respectively; whereas plants treated with malathion followed by foramsulfuron + safener (isoxadifen) showed no decreases in biomass yield (Paporisch & Rubin, 2017). The application of nicosulfuron + malathion inhibited the growth of sweet maize plants in 57%; however, when including safener (isoxadifen) in the application, the decrease in plant growth was 20% (Sun et al, 2017). The safener added to the solution induces the expression of genes that codify cytochrome P450 monooxygenase enzymes (Riechers et al, 2010), which metabolize the herbicide transforming it into metabolites without herbicide action (Duhoux et al, 2017).…”

Protective efficacy of phenoxyacetyl oxazolidine derivatives as safeners against nicosulfuron toxicity in maize

“…[21][22][23] Sun et al reported that isoxadifen-ethyl alleviated nicosulfuron injury in maize by enhancing GST activity. 24 Substituted oxazole isoxazole carboxamides protected maize from chlorsulfuron by increasing GST activity and GSH content. 25 The activity of GST was upregulated in the coleoptiles of Triticum tauschii seedlings treated with the safener fluxofenim.…”

“…Sun et al . reported that isoxadifen‐ethyl alleviated nicosulfuron injury in maize by enhancing GST activity 24 . Substituted oxazole isoxazole carboxamides protected maize from chlorsulfuron by increasing GST activity and GSH content 25 .…”