Life Cycle Exposure to Cyhalofop-Butyl Induced Reproductive Toxicity in Zebrafish.

Cyhalofop-butyl (CyB) is a herbicide widely used in paddy fields that may transfer to aquatic ecosystems and cause harm to aquatic organisms. In this study, zebrafish (Danio rerio) were exposed to CyB at environmental concentrations (0.1, 1 and 10 µg/L) throughout their adult life cycle, from embryo to sexual maturity. The effects of CyB on zebrafish growth and reproduction were studied. It was found that female spawning was inhibited, and adult male fertility decreased. In addition, we examined the expression of sex steroid hormones and genes related to the hypothalamus-pituitary-gonad-liver (HPGL) axis. After 150 days of exposure, the hormone balance in zebrafish was disturbed, and the concentrations of 17ß-estradiol (E2) and vitellogenin (VTG) were decreased. Changes in sex hormone were regulated by the expression of genes related to the HPGL axis. These results confirmed that long-term exposure to CyB at environmental concentrations can damage the reproductive capacity of zebrafish by disrupting the transcription of genes related to the HPGL axis. Overall, these data may provide a new understanding of the reproductive toxicity of long-term exposure to CyB in zebrafish parents and offspring.

The Metabolism of a Novel Cytochrome P450 (CYP77B34) in Tribenuron-Methyl-Resistant Descurainia sophia L. to Herbicides with Different Mode of Actions.

Descurainia sophia L. (flixweeds) is a noxious broad-leaf weed infesting winter wheat fields in China that has evolved high resistance to tribenuron-methyl. In this work, a brand new gene CYP77B34 was cloned from tribenuron-methyl-resistant (TR) D. sophia and transferred into Arabidopsis thaliana, and the sensitivities of Arabidopsis with or without the CYP77B34 transgene to herbicides with a different mode of actions (MoAs) were tested. Compared to Arabidopsis expressing pCAMBIA1302-GFP (empty plasmid), Arabidopsis transferring pCAMBIA1302-CYP77B34 (recombinant plasmid) became resistant to acetolactate synthase (ALS)-inhibiting herbicide tribenuron-methyl, protoporphyrinogen oxidase (PPO)-inhibiting herbicides carfentrazone-ethyl and oxyfluorfen. Cytochrome P450 inhibitor malathion could reverse the resistance to tribenuron-methyl, carfentrazone-ethyl and oxyfluorfen in transgenic Arabidopsis plants. In addition, the metabolic rates of tribenuron-methyl in Arabidopsis expressing CYP77B34 were significantly higher than those in Arabidopsis expressing pCAMBIA1302-GFP. Other than that, the transgenic plants showed some tolerance to very-long-chain fatty acid synthesis (VLCFAs)-inhibiting herbicide pretilachlor and photosystem (PS) II-inhibiting herbicide bromoxynil. Subcellular localization revealed that the CYP77B34 protein was located in the endoplasmic reticulum (ER). These results clearly indicated that CYP77B34 mediated D. sophia resistance to tribenuron-methyl and may have been involved in D. sophia cross-resistance to carfentrazone-ethyl, oxyfluorfen, pretilachlor and bromoxynil.

Tribenuron-methyl-resistant Descurainia sophia L. exhibits negative cross-resistance to imazethapyr conferred by a Pro197Ser mutation in acetolactate synthase and reduced metabolism.

BACKGROUND: Descurainia sophia L. is one of the most notorious weeds infesting winter wheat in China. Mutations at Pro197 in acetolactate synthase (ALS) results in resistance of D. sophia to tribenuron-methyl and cross-resistance to many ALS inhibitors. Negative cross-resistance to imazethapyr was observed in tribenuron-methyl-resistant (TR) D. sophia with the Pro197Ser mutation in a previous study. In the present research, another TR D. sophia with the Pro197Ser mutation was obtained. To explore the mechanisms of negative cross-resistance, the ALS sensitivity, the absorption and metabolism of imazethapyr in tribenuron-methyl-susceptible (TS) and TR D. sophia were studied. RESULTS: The TR D. sophia population with the Pro197Ser mutation (pHB23) displayed negative cross-resistance to imazethapyr and no cross-resistance to imazamox and imazapic. In contrast, TR D. sophia populations with other Pro197 mutations had no or low resistance to imazethapyr. The ALS in the pHB23 population was more susceptible to imazethapyr than that in the TS population. There was no difference in the absorption of imazethapyr, imazamox, and imazapic between TS and pHB23 plants. However, the metabolism of imazethapyr in TS D. sophia was faster than that in pHB23 plants up to 1 week after treatment. There was no significant difference in the metabolism of imazamox and imazapic between TS and pHB23 plants. CONCLUSION: The TR D. sophia population with the Pro197Ser mutation exhibited negative cross-resistance to imazethapyr, which was likely due to reduced metabolism and increased sensitivity of ALS to imazethapyr. © 2021 Society of Chemical Industry.