Effects of prometryn and acetochlor on arbuscular mycorrhizal fungi and symbiotic system

Prometryn and acetochlor are common herbicides widely used to control weeds in agricultural systems. The impacts of the two herbicides on spore germination, hyphal elongation, the biomass and malondialdehyde content of carrot hairy roots were investigated using a strict in vitro cultivation system associating the Ri T‐DNA‐transferred carrot hairy roots with Glomus etunicatum. Alternatively, root colonization, daughter spore production and the proportion of hyphae with succinate dehydrogenase (SDH) and alkaline phosphatase (ALP) activities were also investigated. No significant impact on spore germination was noted in the presence of acetochlor at all three concentrations tested, while a significant decrease was observed with prometryn only at the highest concentration. Moreover, an inverse correlation was identified between herbicides concentrations and G. etunicatum root colonization and spore production as well as hyphal SDH and ALP activity, with a positive correlation identified among these four factors. Both herbicides exerted negative effects on the arbuscular mycorrhizal (AM) fungus and symbiosis at increasing concentrations, with prometryn apparently more toxic than acetochlor. Furthermore, the AM symbiotic system was shown to improve biomass, reduce malondialdehyde accumulation and ease lipid peroxidation in carrot hairy roots and decrease damage in host plants, thus enhancing plant tolerance to adverse conditions.

Significance and Impact of the Study

In this study, the effect of prometryn and acetochlor on the physiology and metabolic activities of the AM fungus Glomus etunicatum were investigated. Our findings demonstrate for the first time, the impact of the two herbicides at three concentrations (0·1, 1 and 10 mg l^?1) on transformed carrot hairy roots/AM fungus association under strict in vitro culture conditions, which may guide the application of the two herbicides in modern agriculture.     

Translocation and Metabolism of Picloram and 2,4-D in Populus tremula

Translocation and metabolism of 4-amino-3,5,6-trichloropicolinic acid (picloram) and 2,4-dichlorophenoxyacetic acid (2,4-D) in small plants of aspen (Populus tremula L.) were studied. In most experiments ¹⁴C-carboxyl-labelled herbicides were used. Considerable quantities of both herbicides were retained in the treated leaf. Translocation was mainly upwards into the growing shoot tip. Only minute quantities were found in the roots. Injection of the herbicides through a cut stem surface increased the translocation into the roots very little. One of the reasons for the limited downward translocation is considered to be a ready transfer of the herbicides between the phloem and the xylem. Both herbicides were incorporated into complexes from which the active herbicides could be released. However, this complex formation can only partly account for the retention of the herbicides in the treated leaves. The differences in metabolism found between 2,4-D and picloram cannot explain the considerable difference in toxicity between the compounds.     

Behaviour of Herbicides in Dicotyledonous Roots Transformed by Agrobacterium rhizogenes: II. TRANSPORT TO REGENERATED SHOOTS

Mugnier, J. 1988. Behaviour of herbicides in dicotyledonousroots transformed by Agrobacterium rhizogenes. II. Transportto regenerated shoots.—J. exp. Bot. 39: 1057–1064. Regenerated plants from roots of Anagallis arvensis transformedby Agrobacterium rhizogenes were propagated in Petri disheson Murashige and Skoog's medium. The roots were exposed to differentherbicides. We report here the relationship between root uptakeand translocation of the herbicides acting upon the shoots.The results show that regenerated Anagallis arvensis plantspropagated in Petri dishes reflected the situation in normalplants in their responses to symplastic herbicides (aminotriazole,glyphosate, 2,4-D) which have strong bleaching or wilting effects.Sucrose seemed to be the critical driving force by which symplasticherbicides were transported from the root towards the shoot.The results applied to a limited range of environmental conditionssince the transport and performance of apoplastic herbicides(S-triazines, triazinones, substituted ureas) was apparentlylimited by the sucrose and moisture conditions in the Petridish. The mode of transport, in phloem versus xylem, of herbicidewithin a transformed root is discussed. Key words: Agrobacterium rhizogenes, herbicides, root organ culture     

Impairment of carbon metabolism induced by the herbicide glyphosate

The herbicide glyphosate reduces plant growth and causes plant death by inhibiting the biosynthesis of aromatic amino acids. The objective of this work was to determine whether glyphosate-treated plants show a carbon metabolism pattern comparable to that of plants treated with herbicides that inhibit branched-chain amino acid biosynthesis. Glyphosate-treated plants showed impaired carbon metabolism with an accumulation of carbohydrates in the leaves and roots. The growth inhibition detected after glyphosate treatment suggested impaired metabolism that impedes the utilization of available carbohydrates or energy at the expected rate. These effects were common to both types of amino acid biosynthesis inhibitors. Under aerobic conditions, ethanolic fermentative metabolism was enhanced in the roots of glyphosate-treated plants. This fermentative response was not related to changes in the respiratory rate or to a limitation of the energy charge. This response, which was similar for both types of herbicides, might be considered a general response to stress conditions.     

Activité des pyrophosphatases inorganiques acide et alcaline après traitement avec divers herbicides

Various herbicides are applied on seventeen-day-old cucumber seedlings growing in a nutrient solution. After 1 and 3 days, acid and alkaline pyrophosphatase activities are measured in the leaves and the roots of seedlings treated with lethale dosis of atrazine, chlortoluron, ioxynil, MCPA, dicamba, alachlor. The same enzymes are determined after 5 h in seedlings on which previously paraquat and DNOC were pulverised. In the leaves, acid pyrophosphatase activity is stimulated by almost all the herbicides, especially by ioxynil, paraquat and DNOC while alkaline pyrophosphatase remains similar to the controls. The alkaline and acid pyrophosphatase activity in the roots is either unchanged or stimulated or inhibited without any correlation with the various modes of action of the herbicides.     

The adsorption of herbicides by roots

Summary The uptake of five herbicides by the dead roots of six plant species was investigated and it is concluded that the process involved was probably adsorption. The adsorptive capacity of the dry matter of roots was lower than soil organic matter but was of a similar order of magnitude. It is suggested that in some cases adsorption might provide a significant pathway by which herbicides are taken up by the living plant. It seems unlikely that adsorption by roots will normally exert much influence on the herbicide concentration in the soil solution.     

Sulfate transport of excised roots as an index of genotype response to herbicides

The inhibitory action of four herbicides (atrazine, dalapon, moiinate, propanil) on the membrane transport of sulfate by excised roots was evaluated in tolerant ( Oryza saliva ) and susceptible ( Pisam sativum, Hordeum vulgare ) cultivated species, and in a tolerant and susceptible variety of a weed ( Brassica rapa ). A parallelism between the response of the root transport activity and the general response of the genotype was ascertained, irrespective of the metabolic target of the herbicide. The inhibition mechanism of sulfate uptake was either competitive, non competitive, or uncompetitive, but this aspect was not correlated with the response of the genotype to the herbicide. The kinetics of absorption ¹⁴C atrazine by excised roots and by chloroplasts of Brassica rapa were strictly related: the amount of atrazine binding to roots and to chloroplasts was higher in the susceptible than in the resistant variety. The Sevel of atrazine inhibition of sulfate transport in roots was correlated to that of the Hill reaction; both were higher in the susceptible variety. The membrane transport within the roots appears to summarize and anticipate the metabolic response of genotypes to herbicides.     

Phytotoxic and Metabolic Effects of Exogenous Quinate on Pisum sativum L.

Quinate (1,3,4,5-tetrahydroxycyclohexanecarboxylate) is a compound synthesized in plants through a side branch of the shikimate biosynthesis pathway. Plants treated with herbicides that inhibit amino acid biosynthesis (branched-chain and aromatic) accumulate quinate in their leaves. The objective of this study was to evaluate whether quinate mimics the effects of herbicides in plants. In pea plants, exogenous application of quinate through the nutrient solution was compared with leaf spraying at a concentration of 4 and 400 mM, respectively, and evaluated in parallel to the effects of herbicides. The analysis facilitated an assessment of the phytotoxicity and potential use of quinate as a natural herbicide. The application of quinate through the nutrient solution, but not the spray, was lethal, although both treatments affected plant growth. Quinate was absorbed and translocated to other plant organs remote from the application site, and an increase in the levels of aromatic amino acids and caffeic acid (that is, compounds located after quinate in the shikimate biosynthesis pathway) was detected, which indicates that quinate was metabolized and incorporated into the shikimate pathway. Exogenous application of quinate affected the carbohydrate content in the leaves and roots in a way similar to the toxic effects of herbicides. The phytotoxic effects of quinate reported in this study suggest that this compound deregulates the shikimate pathway and mimics some physiological effects described in the mode of action of herbicides inhibiting amino acid biosynthesis.     

Potassium influx and efflux of 2,4-D- and MCPA-treated rice plants

Summary A study was made of the effects of the herbicides 2,4-D (2,4-dichlorophenoxyacetic acid) and MCPA (4-chloro-2-methyl-phenoxyacetic acid) on ion uptake, leakage and growth of rice seedlings. Using isotopically-labelled solutions containing different concentrations of 2,4-D or MCPA, it was established that 10^–4 M 2,4-D or MCPA effectively inhibited potassium ion uptake, while K-ion leakage from the roots occurred only at 10^–3 M. The growth of the rice seedlings was markedly retarded even at low (10^–6 M) concentrations, and the roots and shoots showed different tolerances to the herbicide. At 10^–8 M herbicide, the effects were not injurious, but rather favourable. Reduction in root length by herbicides was not in accordance with dry-matter production.     

“使它隆”对玉米根部不同微生环境细菌群落多样性的影响

【目的】研究除草剂"使它隆"施用后对玉米根部不同微生环境细菌群落结构和多样性的影响。【方法】利用Illumina Miseq高通量测序技术,对玉米根系内生菌、根际和非根际土壤细菌16S rRNA的V4–V5可变区序列进行测定,分析不同生长期喷施除草剂使它隆对玉米土壤细菌及根系内生菌群落结构和多样性的影响。【结果】本研究15个样品共得到544393条有效序列,333565条优质序列。多样本共有OTU分析表明,非根际和根际土壤的群落结构更为相似,在一定程度上说明玉米根部相关细菌的定殖具有选择性并且是从根际到根系逐步专一化。丰度等级曲线和Alpha多样性结果显示非根际和根际土壤群落的丰富度和均匀度较高,而玉米根系内生菌群落的丰富度和均匀度都比较低,且成熟期玉米根系内生菌群落的丰富度在施用除草剂使它隆后下降比较剧烈。群落组成分析发现,使它隆除草后,玉米根部相关细菌各时期在门及属水平上的分布都发生了较大变化。菌群代谢功能预测结果表明玉米生长从苗期到成熟期,微生物的生长压力逐渐加大,需要消耗更多的能量用于新陈代谢和环境适应。【结论】施用除草剂使它隆后会降低玉米根部土壤细菌群落的多样性,使它隆对成熟期玉米根系内生菌群落影响最为显著。     

Weed control and cover crop management affect mycorrhizal colonization of grapevine roots and arbuscular mycorrhizal fungal spore populations in a California vineyard

Arbuscular mycorrhizal (AM) fungi naturally colonize grapevines in California vineyards. Weed control and cover cropping may affect AM fungi directly, through destruction of extraradical hyphae by soil disruption, or indirectly, through effects on populations of mycorrhizal weeds and cover crops. We examined the effects of weed control (cultivation, post-emergence herbicides, pre-emergence herbicides) and cover crops (Secale cereale cv. Merced rye, × Triticosecale cv.Trios 102) on AM fungi in a Central Coast vineyard. Seasonal changes in grapevine mycorrhizal colonization differed among weed control treatments, but did not correspond with seasonal changes in total weed frequency. Differences in grapevine colonization among weed control treatments may be due to differences in mycorrhizal status and/or AM fungal species composition among dominant weed species. Cover crops had no effect on grapevine mycorrhizal colonization, despite higher spring spore populations in cover cropped middles compared to bare middles. Cover crops were mycorrhizal and shared four AM fungal species (Glomus aggregatum, G. etunicatum, G. mosseae, G. scintillans) in common with grapevines. Lack of contact between grapevine roots and cover crop roots may have prevented grapevines from accessing higher spore populations in the middles.     

Root hair infection and nodule to lateral root relationship in lucerne seedlings as influenced by dalapon and amitrole

Summary The effect of two water soluble herbicides, dalapon and amitrole, on the early stages of nodulation was studied. Though curling, deformation and shepherd's crook formation of root hairs were not affected, the number of nodules generally decreased in the presence of the herbicides, accompanied by an increase in the number of lateral roots in some treatments. The results provide experimental evidence in favour of the speculations of some earlier workers on lateral root and nodule relationship in herbicide treated plants.     

In vitro studies on the effects of herbicides on the growth of rhizobia

AIMS: To study the possible adverse effect of herbicides on nodulation and nitrogen fixation in legumes by affecting the nitrogen-fixing rhizobia. METHODS AND RESULTS: Experiments were conducted to study the effect of four herbicides (terbutryn/terbuthylazine, trietazine/simazine, prometryn and bentazone) on the growth of nitrogen-fixing pea rhizobia (Rhizobium leguminosarum) in vitro by measuring optical density. Terbutryn/terbuthylazine, trietazine/simazine and prometryn had an adverse effect on the growth of rhizobia whereas bentazone was safe to rhizobia. CONCLUSIONS: The above herbicides could be used in pea at the recommended rates. SIGNIFICANCE AND IMPACT OF THE STUDY: The adverse effects of herbicides on rhizobia were observed at concentrations not normally expected to occur under field conditions. Further, previously observed adverse effects of these herbicides on nodulation and nitrogen fixation of peas were, possibly, not due to their effects in rhizobia but to their adverse effects on the plant growth itself.     

The influence of chlorsulfuron and metsulfuron methyl on root growth and on the ultrastructure of root tips of germinating maize seeds

Seeds of Zea mays L., germinating in soil, were exposed to very low doses of the sulfonylurea herbicides chlorsulfuron and metsulfuron methyl. At a concentration of 0.012 mg L^–1, chlorsulfuron caused 72% and metsulfuron methyl 55% growth reduction of the young primary roots. Both herbicides also caused obvious injuries to the root tips. Scanning electron microscopic observations of the root tip surfaces indicated an inhibition of slime secretion at a herbicide concentration of 1.5 mg L^–1. Transmission electron microscopy revealed obvious changes to the nuclei and deformation of radial cell walls in the primary root cortex at 0.012 and 1.5 mg L^–1 for both herbicides. Moreover, the secretory cells of the root cap periphery showed partially irregular deposition of premature cell wall or slime material at a concentration of 0.012 mg L^–1 of both herbicides.From the results of our electron microscopic observations we conclude that the primary roots of maize seedlings are seriously affected by extremely low concentrations of even those herbicides which (as chlorsulfuron and metsulfuron methyl) have been developed to inhibit the growth of dicotyledonous weeds. Moreover, we suggest that the frequently observed growth retardation of crop seedlings is a consequence of early root tip injuries caused by herbicide residues in the soil. ei]H Lambers     

Detoxification of herbicides in Phragmites australis

Unintentional loss of herbicides into drainage ditches, shores or other waterbodies may cause large problems in farmland. Therefore strategies for the phytoremediation of agrochemicals and especially herbicides have become a topic of great interest in many agricultural areas. However, in order to establish effective biological pollution control, information on the detoxification capacity of riparian plants and aquatic macrophytes (e.g., Phragmites australis) is important to build up effective buffer stripes. We determined the detoxification capacity of Phragmites australis roots and leaves for the conjugation of agrochemicals to glutathione by assaying the model substrate CDNB as well as the herbicides fenoxaprop-P, propachlor, pethoxamid and terbuthylazine. Specific GST activities were always higher in the rhizomes (6.78 +/- 0.88 microkat/mg protein for CDNB) than in leaves (1.08 +/- 0.21 microkat/mg protein). The detoxification capacity is distributed across an array of GST isoforms. In summary, Phragmites australis seems to be efficient in herbicide detoxification and a good candidate for phytoremediation of effluents from agricultural sites.     

化学除草剂对农田生物群落的影响

从直接作用和间接作用两个方面,在个体、种群和群落3个水平上综述了化学除草剂对农田植物、动物和微生物群落的影响,并提出了今后需要加强研究的几个问题(1)残留在作物和杂草植株内的除草剂及其代谢产物通过食物链和生物富集作用对农田动物群落各级消费者造成的影响;(2)非作物生境使用化学除草剂对毗邻作物生境天敌群落的影响,以及作物生境使用除草剂对邻近非作物生境天敌群落的影响;(3)由除草剂长期使用引起的杂草群落演替、多样性下降、地表覆盖物和地下生物量减少对土壤动物和微生物群落的物种组成、分布、丰富度及其生态功能的影响;(4)化学除草剂与杀虫剂和化肥等其他农用化学品对农田生物群落的联合作用。     

Both foliar and residual applications of herbicides that inhibit amino acid biosynthesis induce alternative respiration and aerobic fermentation in pea roots

The objective of this work was to ascertain whether there is a general pattern of carbon allocation and utilisation in plants following herbicide supply, independent of the site of application: sprayed on leaves or supplied to nutrient solution. The herbicides studied were the amino acid biosynthesis‐inhibiting herbicides (ABIH): glyphosate, an inhibitor of aromatic amino acid biosynthesis, and imazamox, an inhibitor of branched‐chain amino acid biosynthesis. All treated plants showed impaired carbon metabolism; carbohydrate accumulation was detected in both leaves and roots of the treated plants. The accumulation in roots was due to lack of use of available sugars as growth was arrested, which elicited soluble carbohydrate accumulation in the leaves due to a decrease in sink strength. Under aerobic conditions, ethanol fermentative metabolism was enhanced in roots of the treated plants. This fermentative response was not related to a change in total respiration rates or cytochrome respiratory capacity, but an increase in alternative oxidase capacity was detected. Pyruvate accumulation was detected after most of the herbicide treatments. These results demonstrate that both ABIH induce the less‐efficient, ATP‐producing pathways, namely fermentation and alternative respiration, by increasing the key metabolite, pyruvate. The plant response was similar not only for the two ABIH but also after foliar or residual application.     

Proteomic analysis of root meristems and the effects of acetohydroxyacid synthase-inhibiting herbicides in the root of Medicago truncatula

Quantitative proteome analyses of meristematic and nonmeristematic tissues from Medicago truncatula primary and lateral roots and meristem tissues from plants treated with acetohydroxyacid synthase-inhibiting herbicides were made. The accumulation of 81 protein spots changed in meristematic and nonmeristematic tissues and 51 protein spots showed significant changes in accumulation in herbicide-treated meristems. Identified proteins indicate two trends, (i) increased accumulation of cell division and redox-mediating proteins in meristems compared to nonmeristematic tissues and (ii) increased accumulation of pathogenesis-related and decreased accumulation of metabolic proteins in herbicide-treated roots.     

Morphological and anatomical changes in the roots of apple seedlings treated with morphactin IT 3456 and α-naphthalene acetic acid (NAA)

On the roots of the unchilled apple seedlings treated with morphactin many deformed adventitious shoots were formed, whereas when the roots were dipped in the mixture of morphactin and NAA more adventitious roots were produced than when only NAA was used. The growth of these lateral roots was greatly inhibited. Similar interaction of NAA with morphactin in the development of roots was obtained when the chilled seedlings were treated with these growth regulators before the buds developed. The sections of the roots from all the treatments were made and the anatomy studied.     

Degradation of Herbicides in the Tropical Marine Environment: Influence of Light and Sediment

Widespread contamination of nearshore marine systems, including the Great Barrier Reef (GBR) lagoon, with agricultural herbicides has long been recognised. The fate of these contaminants in the marine environment is poorly understood but the detection of photosystem II (PSII) herbicides in the GBR year-round suggests very slow degradation rates. Here, we evaluated the persistence of a range of commonly detected herbicides in marine water under field-relevant concentrations and conditions. Twelve-month degradation experiments were conducted in large open tanks, under different light scenarios and in the presence and absence of natural sediments. All PSII herbicides were persistent under control conditions (dark, no sediments) with half-lives of 300 d for atrazine, 499 d diuron, 1994 d hexazinone, 1766 d tebuthiuron, while the non-PSII herbicides were less persistent at 147 d for metolachlor and 59 d for 2,4-D. The degradation of herbicides was 2–10 fold more rapid in the presence of a diurnal light cycle and coastal sediments; apart from 2,4-D which degraded more slowly in the presence of light. Despite the more rapid degradation observed for most herbicides in the presence of light and sediments, the half-lives remained > 100 d for the PS II herbicides. The effects of light and sediments on herbicide persistence were likely due to their influence on microbial community composition and its ability to utilise the herbicides as a carbon source. These results help explain the year-round presence of PSII herbicides in marine systems, including the GBR, but more research on the transport, degradation and toxicity on a wider range of pesticides and their transformation products is needed to improve their regulation in sensitive environments.