Circadian response of annual weeds to glyphosate and glufosinate

Five field experiments were conducted in 1998 and 1999 in Minnesota to examine the influence of time of day efficacy of glyphosate [N-(phosphonomethyl)glycine] and glufosinate [2-amino-4-(hydroxymethyl-phosphinyl)butanoic acid] applications on the control of annual weeds. Each experiment was designed to be a randomized complete block with four replications using plot sizes of 3×9 m. Glyphosate and glufosinate were applied at rates of 0.421 kg ae/ha and 0.292 kg ai/ha, respectively, with and without an additional adjuvant that consisted of 20% nonionic surfactant and 80% ammonium sulfate. All treatments were applied with water at 94 L/ha. Times of day for the application of herbicide were 06:00h, 09:00h, 12:00h, 15:00h, 18:00h, 21:00h, and 24:00h. Efficacy was evaluated 14 d after application by visual ratings. At 14 d, a circadian response to each herbicide was found, with greatest annual weed control observed with an application occurring between 09:00h and 18:00h and significantly less weed control observed with an application at 06:00h, 21:00h, or 24:00h. The addition of an adjuvant to both herbicides increased overall efficacy, but did not overcome the rhythmic time of day effect. Results of the multiple regression analysis showed that after environmental temperature, time of day was the second most important predictor of percent weed kill. Thus, circadian timing of herbicide application significantly influenced weed control with both glyphosate and glufosinate.     

Effect of glyphosate contaminated feed on rumen fermentation parameters and in sacco degradation of grass hay and corn grain

Four rumen fistulated wethers were used to investigate the effect of glyphosate contaminated feed on rumen fermentation. The rations were based on corn silage, urea and a vitamin-mineral premix, either in the absence or presence of 0.77?g glyphosate per kg DM. Furthermore, rations were fed either with or without aromatic amino acid supplementation. During four periods of 28 days, sheep received each of the four dietary treatments according to a Latin square. After 14 days of adaptation rumen fermentation parameters (pH, ammonia, volatile fatty acids) were measured on day 15 over a five-hour period after the morning feeding. The remaining 13 days served for in sacco degradation studies with grass hay and corn grain. Ammonia (NH₃) and pH of rumen fluid were within the normal range for all dietary treatments (NH₃: 9.1 – 32.3?mmol·l^???1, pH: 6.2 – 6.7). Neither rumen fermentation parameters nor in sacco DM and NDF degradation of incubated feedstuffs were significantly affected by glyphosate, with or without aromatic amino acid supplementation. Kinetic profiles of the in sacco dry matter and NDF degradation of grass hay were almost identical for the dietary treatments.     

Response of <Emphasis Type="Italic">Phragmites</Emphasis> to environmental parameters associated with treatments

This multi-year study evaluated the response of invasive Phragmites australis to changes in pore water geochemistry associated with tidal enhancement, alone or in combination with other prescribed management regimes used by the US Fish and Wildlife Service. A pilot study was conducted prior to the treatment experiment that showed a negative correlation between the growth of Phragmites and cation concentrations in a transitional vegetation zone. In the targeted 535-acre brackish-water impoundment (East Pool) where Phragmites dominated, the soil water chemistry was changed by introducing tidal salt water through water control structures in June of 1999. Soil profiles, pH, salinity and cation concentration data in addition to Phragmites height and density data were collected both before and after the treatments were imposed, where possible. It was generally observed that a soil water salinity above ∼28 would be needed to maintain the reduction of Phragmites and to support its replacement by salt marsh species. In the tidal water manipulated experimental macroplots, the soil water salinity changed from 7.1 to 32 on average between 1999 and 2001. The reduction of the average height of Phragmites ranged from 25% to 84% for different treatment combinations, while untreated sites exhibited a slight increases in height. The reduction in average live density ranged from 51% to 87% for different treatment combinations. The greatest reduction of Phragmites density and height resulted when tidal enhancement was followed by a prescribed burn in the winter. Also, significant negative correlations were observed between Phragmites height and the main cations associated with tidal salt water including Mg²⁺, Na⁺ and K⁺ and to a lesser extent Ca²⁺. pH did not change drastically with the introduction of tidal water over the period of 1999–2001 and did not appear to play a significant role in changing the growth of Phragmites. A reduction of soil adhesiveness associated with the decay of Phragmites roots was observed after a two month period in 2001 when plants were submerged in standing water. This points to the need to maintain tidal exchange to promote a gradual transition from a Phragmites-dominated system to a Spartina-dominated system. Towards the end of the growing season in 2001, Spartina patens and Distichlis spicata had begun to ramify into the center of the island patches.     

Engineering tropane alkaloid production and glyphosate resistance by overexpressing AbCaM1 and G2-EPSPS in Atropa belladonna

Atropa belladonna is an important industrial crop for producing anticholinergic tropane alkaloids (TAs). Using glyphosate as selection pressure, transgenic homozygous plants of A. belladonna are generated, in which a novel calmodulin gene (AbCaM1) and a reported EPSPS gene (G2-EPSPS) are co-overexpressed. AbCaM1 is highly expressed in secondary roots of A. belladonna and has calcium-binding activity. Three transgenic homozygous lines were generated and their glyphosate tolerance and TAs’ production were evaluated in the field. Transgenic homozygous lines produced TAs at much higher levels than wild-type plants. In the leaves of T2GC02, T2GC05, and T2GC06, the hyoscyamine content was 8.95-, 10.61-, and 9.96 mg/g DW, the scopolamine content was 1.34-, 1.50- and 0.86 mg/g DW, respectively. Wild-type plants of A. belladonna produced hyoscyamine and scopolamine respectively at the levels of 2.45 mg/g DW and 0.30 mg/g DW in leaves. Gene expression analysis indicated that AbCaM1 significantly up-regulated seven key TA biosynthesis genes. Transgenic homozygous lines could tolerate a commercial recommended dose of glyphosate in the field. In summary, new varieties of A. belladonna not only produce pharmaceutical TAs at high levels but tolerate glyphosate, facilitating industrial production of TAs and weed management at a much lower cost.     

Sorption of Glyphosate on Soil Components: The Roles of Metal Oxides and Organic Materials

Predicting the behavior, fate, and transport potential of a herbicide in any soil involves understanding the sorption characteristics. The sorption characteristics of glyphosate (GPS) on soil and their main components were investigated, indicating that the mineral phase is more important than the organic carbon in adsorption of GPS. Sorption isotherms were determined from each component using the batch equilibrium method at various concentrations (5, 10, 15, 20, 25, and 30 mg L^?1) and sorption affinity of GPS was approximated by the Freundlich equation. The sorption strength K _f [mg kg^?1 (L mg^?1)^?n] across the various components ranged from 2.1–134.9 while the organic carbon-normalized Freundlich sorption capacity values, K _foc, ranged from 1.28–3.53 mg kg^?1-OC/(mg L^?1)ⁿ. Infrared Fourier transform spectroscopy (FTIR) of the components showed significant structural differences. The results suggest that the presence of the oxides and hydroxides iron, in particular in soil solutions, enhanced GPS adsorption. They also suggest that reduction in OC% due to various treatments may enhance the remobilization of GPS into the aqueous phase (i.e., groundwater), though at different rates. Comparatively, contribution of surface area to the adsorption of GPS on the various components proved more significant than contents of organic carbon.     

Integration of Herbicides with Arthropod Biocontrol Agents for Weed Control

Classical biological control of weeds using arthropods is being attempted on a large scale in a number of countries, sometimes with spectacularly successful outcomes. However, in many cases biocontrol is not completely effective and use of herbicides on weeds continues to occur, either in the presence of biocontrol agents or as an alternative to them. The ways in which the two techniques may interact are discussed, including direct toxicity of herbicides to biocontrol agents, responses to death of host plants and responses to sublethal changes caused by herbicides with different modes of action. A literature review for selected weed taxa showed that the great majority of publications relate to either chemical or to biological control techniques separately, with integration of the two seldom addressed. Possible reasons for this situation are discussed and some suggestions for future priorities are made.     

突变肠杆菌株NRS-1中5个草甘膦逆境应答基因的克隆与功能研究

【目的】微生物对草甘膦的抗性受复杂的遗传体系调控,涉及靶基因和大量相关调控基因。对肠杆菌属细菌NRS-1突变菌株在高浓度草甘膦逆境下的5个重要差异表达基因进行功能研究,以期深入了解非靶标基因在抗草甘膦微生物的作用特点,为发掘优异基因资源,服务抗草甘膦转基因生物育种提供参考。【方法】NRS-1的差异表达基因可能在蛋白质合成、代谢、细胞膜等水平发挥作用,保护细胞免受高浓度草甘膦逆境,因此分别选取易位酶延伸因子fus A、丁二酸脱氢酶sdh A、胸苷磷酸化酶deo A、鸟氨酸氨甲酰转移酶arg F、周质蛋白osm Y进行克隆,采用大肠杆菌原核表达、转化拟南芥实验研究其功能,并通过细菌双杂及KEGG pathway分析基因间互作特点。【结果】在明确5个基因结构特点基础上,通过大肠杆菌原核表达及转基因拟南芥鉴定,发现这5个基因及草甘膦的靶基因5-烯醇式丙酮莽草酸-3-磷酸合成酶基因aro A对提高2种生物的草甘膦耐性均有不同程度的作用,其中arg F、deo A的抗性较好,与aro A相当,表明在应对草甘膦逆境时,芳香族、含有胸腺嘧啶氨基酸及精氨酸的合成代谢通路可能起重要作用;利用基因互作与KEGG分析发现5个基因与靶基因aro A间形成复杂的调控网络,但无直接的蛋白互作。【结论】NRS-1的5个差异表达基因对草甘膦逆境具有抗性,arg F、deo A优于其他3个基因,其与靶基因aro A间表现复杂的基因互作关系。     

Glyphosate Inhibits PPAR Gamma Induction and Differentiation of Preadipocytes and is able to Induce Oxidative Stress

Glyphosate‐based herbicides (GF) are extensively used for weed control. Thus, it is important to investigate their putative toxic effects. We have reported that GF at subagriculture concentrations inhibits proliferation and differentiation to adipocytes of 3T3‐L1 fibroblasts. In this investigation, we evaluated the effect of GF on genes upregulated during adipogenesis. GF was able to inhibit the induction of PPAR gamma, the master gene in adipogenesis but not C/EBP beta, which precedes PPAR gamma activation. GF also inhibited differentiation and proliferation of another model of preadipocyte: mouse embryonic fibroblasts. In exponentially growing 3T3‐L1 cells, GF increased lipid peroxidation and the activity of the antioxidant enzyme, superoxide dismutase. We also found that proliferation was inhibited with lower concentrations of GF when time of exposure was extended. Thus, GF was able to inhibit proliferation and differentiation of preadipocytes and to induce oxidative stress, which is indicative of its ability to alter cellular physiology.     

Resistance to glyphosate in the cyanobacterium <Emphasis Type="Italic">Microcystis aeruginosa</Emphasis> as result of pre-selective mutations

Adaptation of Microcystis aeruginosa (Cyanobacteria) to resist the herbicide glyphosate was analysed by using an experimental model. Growth of wild-type, glyphosate-sensitive (G^s) cells was inhibited when they were cultured with 120 ppm glyphosate, but after further incubation for several weeks, occasionally the growth of rare cells resistant (G^r) to the herbicide was found. A fluctuation analysis was carried out to distinguish between resistant cells arising from rare spontaneous mutations and resistant cells arising from other mechanisms of adaptation. Resistant cells arose by rare spontaneous mutations prior to the addition of glyphosate, with a rate ranging from 3.1 × 10⁻⁷ to 3.6 × 10⁻⁷ mutants per cell per generation in two strains of M. aeruginosa; the frequency of the G^r allele ranged from 6.14 × 10⁻⁴ to 6.54 × 10⁻⁴. The G^r mutants are slightly elliptical in outline, whereas the G^s cells are spherical. Since G^r mutants have a diminished growth rate, they may be maintained in uncontaminated waters as the result of a balance between new resistants arising from spontaneous mutation and resistants eliminated by natural selection. Thus, rare spontaneous pre-selective mutations may allow the survival of M. aeruginosa in glyphosate-polluted waters via G^r clone selection.