农药中色素合成抑制剂的研究和应用进展

光合作用在植物的生长过程中起着至关重要的作用,以光合色素生物合成过程中的酶作为靶标,是研发除草剂的一个重要方向和热点。其中原卟啉原氧化酶(PPO),八氢番茄红素去饱和酶(PDS),ζ-胡萝卜素去饱和酶(ZDS),对羟苯基丙酮酸双氧化酶(HPPD)等作为除草剂靶酶非常成功。本文综述了近年来农药中色素合成抑制剂的作用机制及最新应用进展,并展望未来的发展趋势。     

新一代原卟啉原氧化酶抑制型除草剂的发现

原卟啉原氧化酶抑制性除草剂的研究开发已有30余年历史。在1970～1980年主要集中于二苯醚类、哮二唑酮类和酞酰亚胺类等化合物的研究，但当时对其作用机理了解甚少。此后，在二十世纪八十年代美国FMC公司进一步研究发现了几类新型原卟啉原氧化酶抑制剂，包括两种新型芳基三唑啉酮类除草剂磺酰三唑酮（sulfentrazone）和三唑酮草酯（carfentrazone-ethyl），     

原卟啉原氧化酶抑制剂类除草剂研究进展

概述了原卟啉原氧化酶抑制剂类除草剂作用机理、结构-活性关系研究进展以及新品种开发情况。     

原卟啉原氧化酶抑制剂的结构演变

原卟啉原氧化酶抑制剂类除草剂是近年来发展最快的除草剂品系之一。这类除草剂引起植物的典型生理变化主要有生长抑制、叶绿素降解、原卟啉IX积累、膜降解产生短链碳氢化合物。其基本特征是活性氧导致过氧化作用，因此又可称为过氧化除草剂（peroxidizing herbicide）。由于此类除草剂以叶绿素为作用点．确保了动植物之间的选择毒性，具有超高效、低毒的特点，成为新型除草剂的热点。早期的二苯醚类除草剂是这类除草剂的代表，     

靶标酶在除草剂研究与开发中的作用

大多数除草剂都是通过特殊酶的抑制而产生杀草作用的。根据作用靶标对除草剂进行分类,了解靶标酶的作用机理及特性,对于新型除草剂的设计和杂草抗性的防治能够起到很大的帮助。本文介绍了谷胱甘肽转移酶(GST)、细胞色素P450酶、乙酰乳酸合成酶(ALS)、乙酞辅酶A羧化酶(ACCace)的研究进展。并分别从酶的生理功能、酶学特征、抑制剂作用机理、抑制剂的研究、抗性等方面进行了不同程度的阐述。     

除草剂安全剂作用机理研究进展

除草剂安全剂是一类可在不影响除草剂对靶标杂草活性的前提下,有选择性地保护作物免受除草剂伤害的特殊用途化合物,有关安全剂作用机理的研究对新安全剂的开发具有重要意义。目前关于除草剂安全剂的作用机理主要有4种观点:1）影响除草剂在作物体内的吸收和转运;2）与除草剂竞争靶标位点;3）影响靶标酶的活性;4）增强作物对除草剂的代谢。文章对近年来安全剂作用机理及安全剂对杂草的影响等研究进展进行了综述,并分析了当前存在的问题及未来的研究方向,旨在为深入研究安全剂的作用机理及新安全剂开发提供参考。     

乙酰辅酶A羧化酶抑制剂类除草剂与杂草的抗药性

乙酰辅酶A羧化酶(ACCase)是芳氧苯氧基丙酸类(AOPP)除草剂和环己烯酮类(CHD)除草剂的作用靶标酶，这类除草剂对禾本科杂草有优异的防除效果，属于超高效型除草剂，使用范围较广，但同时也发现连续使用该类除草剂，杂草容易产生抗药性。本文概述了AOPP和CHD类除草剂的现状、作用机理及抗该类除草剂杂草的分布、危害，并探讨了杂草对该类除草剂的抗性机理、抗性控制等。     

新型原卟啉原氧化酶抑制剂Y11049的作用特性

为明确新型原卟啉原氧化酶(PPO)抑制剂Y11049[化学名称为2-((6-氟-5-(3-甲基-2,6-二氧代-4-三氟甲基-3,6-二氢嘧啶-1(2H)-基)苯并[d]噻唑-2-基)硫代)丙酸乙酯]的作用特性,本研究以同类型药剂苯嘧磺草胺为对照,选择对Y11049敏感的几种阔叶杂草为测试靶标,采用室内生物测定法,分别...     

除草剂安全剂对作物细胞色素P450及其他酶活性和水平的影响

综述了除草剂安全剂对作物中参与除草剂解毒作用的酶以及作为除草剂作用靶标位点酶水平与活性的影响。安全剂能增强细胞色素P450酶系统活性,诱导P450在除草剂降解中的作用;增加作物体内谷胱甘肽的含量,从而促进除草剂与谷胱甘肽的轭合而发挥解毒作用;降低由于除草剂对乙酰乳酸合成酶的抑制作用而引起的植物毒性等。     

玉米田化学除草剂的发展及其在我国的应用

最近20余年,除草剂品种的不断发展带动了玉米田化学除草技术的不断完善,但传统除草剂品种仍是玉米田除草剂使用的主体.在以原嘌呤原氧化酶(Protox)和对羟苯基丙酮酸二氧化酶(HPPD)为靶标逐渐成为新除草剂开发热点的同时,转基因耐除草剂玉米的发展将促进灭生性除草剂的使用.目前,我国玉米田除草剂品种仅有莠去津、甲草嗪、甲草胺、乙草胺、异丙甲草胺、异丙草胺、噻吩磺隆、烟嘧磺隆、氟乐灵、2,4-D等10余种,其中长残效除草剂莠去津用量过大,存在着巨大的隐患.我国玉米田除草剂急需发展短残效品种和茎叶处理剂,提高玉米田除草的灵活性和选择性,在适当引进新除草剂品种的基础上,着重开发用于玉米田的除草剂混合制剂及提高使用技术,研制和应用与之相适应的环境友好型的除草剂增效剂和安全剂,改进除草剂剂型.     

Inhibition profile of trifludimoxazin towards PPO2 target site mutations

BACKGROUND

Target site resistance to herbicides that inhibit protoporphyrinogen IX oxidase (PPO; EC 1.3.3.4) has been described mainly in broadleaf weeds based on mutations in the gene designated protoporphyrinogen oxidase 2 (PPO2) and in one monocot weed species in protoporphyrinogen oxidase 1 (PPO1). To control PPO target site resistant weeds in future it is important to design new PPO-inhibiting herbicides that can control problematic weeds expressing mutant PPO enzymes. In this study, we assessed the efficacy of a new triazinone-type inhibitor, trifludimoxazin, to inhibit PPO2 enzymes carrying target site mutations in comparison with three widely used PPO-inhibiting herbicides.

RESULTS

Mutated Amaranthus spp. PPO2 enzymes were expressed in Escherichia coli, purified and measured biochemically for activity and inhibition kinetics, and used for complementation experiments in an E. coli hemG mutant that lacks the corresponding microbial PPO gene function. In addition, we used ectopic expression in Arabidopsis and structural PPO protein modeling to support the enzyme inhibition study. The generated data strongly suggest that trifludimoxazin is a strong inhibitor both at the enzyme level and in transgenics Arabidopsis ectopically expressing PPO2 target site mutations.

CONCLUSION

Trifludimoxazin is a potent PPO-inhibiting herbicide that inhibits various PPO2 enzymes carrying target site mutations and could be used as a chemical-based control strategy to mitigate the widespread occurrence of PPO target site resistance as well as weeds that have evolved resistance to other herbicide mode of actions. © 2022 BASF SE and The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Photodynamic herbicides VIII. Mandatory requirement of light for the induction of protoporphyrin IX accumulation in acifluorfen-treated cucumber

It is shown that continuous illumination is mandatory for the induction of tetrapyrrole accumulation in acifluorfen-sodium-treated plants and for the photosensitization of tetrapyrrole-dependent photodynamic damage. At low concentrations of acifluorfen-sodium (up to 20 μM), photoporphyrin IX appears to be the major light-induced tetrapyrrole that accumulates in the treated plants. At higher concentrations of acifluorfen-sodium, monovinyl chlorophyllide a accumulates in addition to protoporphyrin IX. In the light, the development of photodynamic injury appears to be directly related to the accumulation of the light-induced tetrapyrroles. For example when acifluorfen-sodium-treated plants are returned to darkness, or are treated with tetrapyrrole biosynthesis inhibitors, tetrapyrrole accumulation and photodynamic injury come to a halt. In-vivo and in-organello studies failed, however, to support the commonly held hypothesis that the induction of tetrapyrrole accumulation in the light, in acifluorfen-sodium-treated plants, is only dependent on the inhibition of protoporphyrinogen oxidase. Indeed, when plastids capable of very high rates of tetrapyrrole biosynthesis and accumulation were incubated with δ-aminolevulinic acid and acifluorfen-sodium, either in darkness or in the light, a severe inhibition of protoporphyrin IX and total terapyrrole formation was observed. Althoung these results are compatible with the inhibition of tetrapyrrole formation by acifluorfensodium at the level of protoporphyrinogen oxidase, they indicate that, in addition to that inhibition, other cuellular processes are probably involved in the light-dependent accumulation of protoporphyrin IX in acifluorfensodium-treated plants.     

Quinone activation of protoporphyrinogen oxidase of barley plastids

Protoporphyrinogen oxidase catalyzing the oxidation of protoporphyrinogen to protoporphyrin is the target enzyme for several highly active herbicides. The plastidic plant enzyme under normal conditions uses oxygen as electron acceptor. Duroquinone, however, can be an alternative electron acceptor of protoporphyrinogen oxidase of barley plastids. In this respect the enzyme from the plastids may be an evolutionary intermediate between bacterial enzymes coupled to ubiquinone and mammalian mitochondrial enzymes coupled to oxygen.     

Resistance of a soybean cell line to oxyfluorfen by overproduction of mitochondrial protoporphyrinogen oxidase

The diphenyl ether herbicide oxyfluorfen (2-chloro-4-trifluoromethylphenyl 3-ethoxy-4-nitrophenyl ether) inhibits protoporphyrinogen oxidase (Protox) which catalyzes the oxidation of protoporphyrinogen IX (Protogen) to protoporphyrin IX (Proto IX), the last step of the common pathway to chlorophyll and haeme biosynthesis. We have selected an oxyfluorfen-resistant soybean cell line by stepwise selection methods, and the resistance mechanism has been investigated. No growth inhibition was observed in resistant cells at a concentration of 10(-7) M oxyfluorfen, a concentration at which normal cells did not survive. While the degree of inhibition of total extractable Protox by oxyfluorfen was the same in both cell types, the enzyme activity in the mitochondrial fraction from non-treated resistant cells was about nine-fold higher than that from normal cells. Northern analysis of mitochondrial Protox revealed that the concentration of mitochondrial Protox mRNA was much higher in resistant cells than that in normal cells. There were no differences in the absorption and metabolic breakdown of oxyfluorfen. The growth of resistant cells was also insensitive to oxadiazon [5-tert-butyl-3-(2,4-dichloro-5-isopropoxyphenyl)-1,3,4-oxadiazol-2-(3H)- one], the other chemical class of Protox inhibitor. Therefore, the resistance of the selected soybean cell line to oxyfluorfen is probably mainly due to the overproduction of mitochondrial Protox.     

Herbicide safety relative to common targets in plants and mammals

Most modern herbicides have low mammalian toxicity. One of the reasons for this safety is that the target site for the herbicides is not often present in mammals. There are approximately 20 mechanisms of action that have been elucidated for herbicides. Of these, some do share common target sites with mammals. The mechanisms include formation of free radicals, protoporphyrinogen oxidase (PROTOX), glutamine synthetase (GS) and 4-hydroxyphenylpyruvate dioxygenase (HPPD). PROTOX, HPPD and GS inhibitors have been shown to inhibit these enzymes in both plants and mammals and there are measurable effects in mammalian systems. However, the consequences of inhibiting a common target site in plants can be quite different than in animals. What may be a lethal event in plants, eg inhibition of HPPD, can have a beneficial effect in mammals, eg treatment for tyrosinemia type I. These chemicals also have low mammalian toxicity due to rapid metabolism and/or excretion of the herbicide from mammalian systems.     

Use of Myxococcus xanthus protoporphyrinogen oxidase as a selectable marker for transformation of rice

Protoporphyrinogen oxidase (PPO) is the target enzyme of peroxidizing herbicides. The overexpression of Myxococcus xanthus PPO (Mx PPO) confers a high level of herbicide resistance in rice. Among the peroxidizing herbicides, butafenacil has an efficiency ∼1000-fold that of oxadiazon, as judged by calli susceptibility tests upon herbicide treatment. Butafenacil (0.1 μM) was used to select transgenic rice plants expressing Mx PPO under the control of the constitutive maize ubiquitin promoter. The ectopic expression of the Mx PPO transgene was investigated in the T₀ generation by Northern blot and Western blot analysis. The T₀ transgenic plants expressing the Mx PPO gene were resistant to butafenacil based on in vitro leaf disk and in vivo foliar spray tests.     

Protoporphyrinogen oxidase inhibitor herbicide effects on pythium root rot of sugarcane, pythium species, and the soil microbial community

ABSTRACT The effects of three protoporphyrinogen oxidase inhibitor herbicides, azafenidin, flumioxazin, and sulfentrazone, on Pythium root rot of sugarcane and the soil microbial community were evaluated in greenhouse experiments. Herbicides were applied as foliar and soil treatments. There were no consistent effects on plant growth or disease parameters. However, some herbicide treatments affected the relative frequency of isolation of Pythium spp. from roots and reduced colonization by the pathogenic species Pythium arrhenomanes. A comparison of sole carbon source utilization profiles indicated that soil-applied herbicides altered the functional diversity of the soil microbial community, with some variation depending on herbicide used. All three herbicides inhibited the in vitro mycelial growth of P. arrhenomanes, P. aphanidermatum, and P. ultimum. Active ingredients were less inhibitory than formulated product for azafenidin and flumioxazin but not for sulfentrazone.     

Expression of human protoporphyrinogen oxidase in transgenic rice induces both a photodynamic response and oxyfluorfen resistance

A human protoporphyrinogen oxidase (Protox) coding sequence under the control of a ubiquitin promoter was introduced into rice to determine whether transgenic rice overexpressing the human Protox gene exhibits resistance against a peroxidizing herbicide. The transgenic rice lines (H3, H4, H5, H6, H9, and H10) transcribed the human Protox mRNA, whereas hybridizing RNA band was not detected in wild-type rice, indicating that the human Protox gene had been successfully transmitted into transgenic rice plants. The transgenic lines H9 and H10 showed growth retardation and light-dependent formation of necrotic lesions. Compared with wild-type rice plants, rice with a human Protox gene had increased Protox activity and content of the photosensitizer protoporphyrin IX, and reduced chlorophyll. The photosynthetic efficiency in lines H9 and H10, as indicated by F_v/F_m, was not different from that of wild type. The two transgenic lines had decreased levels of antheraxanthin, lutein, and β-carotene and similar levels of neoxanthin and violaxanthin as compared with wild-type plants. The staining activities of catalase, peroxidase, superoxide dismutase, and glutathione reductase were higher in transgenic lines than in wild type. Line H9 germinated in the presence of 20 μM oxyfluorfen, whereas 2 μM oxyfluorfen inhibited the germination of wild-type seeds. Thus, the transgenic rice plants exhibited enhanced resistance to oxyfluorfen.