Shikimic acid accumulation in field-grown corn (Zea mays) following simulated glyphosate drift

Field studies were conducted in 2001 through 2003 to determine if shikimic acid accumulation could be used to accurately predict yield reductions in field corn exposed to sublethal rates of glyphosate. Glyphosate (0-0.32 kg ae/ha) was applied to corn at the V6 to V8 growth stage. Corn whorls were randomly collected up to 14 days after application (DAA), and shikimic acid accumulation in the whorls was determined using HPLC-UV. Maximum shikimic acid accumulation occurred 3-7 DAA in corn receiving 0.16 and 0.32 kg/ha. Shikimic acid accumulation 3, 5, and 7 DAA did correlate (r = 0.80-0.86) to yield losses from a sublethal application of glyphosate. Shikimic acid accumulation 3, 5, and 7 DAA was better correlated to visual injury at 14 DAA than to yield reductions. Visual injury ratings 14 DAA were a slightly better indicator of potential yield losses (r = 0.93) than shikimic acid accumulation in field-grown corn whorls (r = 0.8-0.86).     

Tolerance and accumulation of shikimic acid in response to glyphosate applications in glyphosate-resistant and nonglyphosate-resistant cotton (Gossypium hirsutum L.).

Measurement of shikimic acid accumulation in response to glyphosate inhibition of 5-enolpyruvylshikimate-3-phosphate synthase is a rapid and accurate assay to quantify glyphosate-induced damage in sensitive plants. Two methods of assaying shikimic acid, a spectrophotometric and a high-performance liquid chromatography (HPLC) method, were compared for their accuracy of recovering known amounts of shikimic acid spiked into plant samples. The HPLC method recovered essentially 100% of shikimic acid as compared with only 73% using the spectrophotometric method. Relative sensitivity to glyphosate was measured in glyphosate-resistant (GR) and non-GR cotton leaves, fruiting branches, and squares (floral buds) by assaying shikimic acid. Accumulation of shikimic acid was not observed in any tissue, either GR or non-GR, at rates of 5 mM glyphosate or less applied to leaves. All tissues of non-GR plants accumulated shikimic acid in response to glyphosate treatment; however, only fruiting branches and squares of GR plants accumulated a slight amount of shikimic acid. In non-GR cotton, fruiting branches and squares accumulated 18 and 11 times, respectively, more shikimic acid per micromolar of translocated glyphosate than leaf tissue, suggesting increased sensitivity to glyphosate of reproductive tissue over vegetative tissue. GR cotton leaves treated with 80 mM of glyphosate accumulated 57 times less shikimic acid per micromolar of translocated glyphosate than non-GR cotton but only 12.4- and 4-fold less in fruiting branches and squares, respectively. The increased sensitivity of reproductive structures to glyphosate inhibition may be due to a higher demand for shikimate pathway products and may provide an explanation for reports of fruit abortion from glyphosate-treated GR cotton.     

Manganese in RR Cotton as Affected by Glyphosate

There is evidence that glyphosate application in soybean tolerant to herbicides could interfere in the manganese (Mn) nutrition of the crop, but there is no information on this effect in cotton plants. This study aimed at assessing manganese accumulation and distribution in cotton as affected by glyphosate application. The experiment was conducted in nutrient solution with four Mn concentrations and two cotton cultivars: conventional NuOpal and NuOpal tolerant to glyphosate (RR). Glyphosate was applied or not to the tolerant cultivar. The inclusion of the glyphosate resistance gene in cotton and herbicide, application increased shikimic acid (ShA) concentration in the plants. Glyphosate application decreased cotton leaf area and the dry matter production of the plant structures. The adverse effects of glyphosate were not overcome with higher Mn rates in the solution.     

Glyphosate effects on phenolic metabolism of nodulated soybean (Glycine max L. merr.).

Glyphosate is a herbicide that blocks the shikimic acid pathway. Three Bradyrhizobium japonicum strains with different sensitivities to glyphosate were used to test the effect of this herbicide on the phenolic metabolism of nodulated soybeans and on the bacteroid nitrogenase activity. Glyphosate caused an inhibition in the bacteroid nitrogenase activity that was related with the sensitivity of the nodule-forming strains. Both leaves and nodules accumulated huge amounts of shikimate and phenolic acids (mainly protocatechuic acid), indicating that the herbicide was translocated to the nodule and disturbed phenolic metabolism. However, this accumulation was not clearly related to the sensitivity of the different strains. Bacteroids from control plants were incubated with the same concentration of shikimate, and phenolic acid accumulated in glyphosate-treated plants. Despite the high levels found in nodules, they were not responsible for the decrease of the nitrogenase activity. Glyphosate by itself caused a small inhibition of the bacteroid nitrogenase activity.     

Aminomethylphosphonic acid accumulation in plant species treated with glyphosate

Aminomethylphosphonic acid (AMPA) is the most frequently detected metabolite of glyphosate in plants. The objective of this study was to determine if there is any correlation of metabolism of glyphosate to AMPA in different plant species and their natural level of resistance to glyphosate. Greenhouse studies were conducted to determine the glyphosate I 50 values (rate required to cause a 50% reduction in plant growth) and to quantify AMPA and shikimate concentrations in selected leguminous and nonleguminous species treated with glyphosate at respective I 50 rates. Coffee senna [ Cassia occidentalis (L.) Link] was the most sensitive ( I 50 = 75 g/ha) and hemp sesbania [ Sesbania herbacea (P.Mill.) McVaugh] was the most resistant ( I 50 = 456 g/ha) to glyphosate. Hemp sesbania was 6-fold and Illinois bundleflower [ Desmanthus illinoensis (Michx.) MacM. ex B.L.Robins. & Fern.] was 4-fold more resistant to glyphosate than coffee senna. Glyphosate was present in all plant species, and its concentration ranged from 0.308 to 38.7 microg/g of tissue. AMPA was present in all leguminous species studied except hemp sesbania. AMPA concentration ranged from 0.119 to 4.77 microg/g of tissue. Shikimate was present in all plant species treated with glyphosate, and levels ranged from 0.053 to 16.5 mg/g of tissue. Non-glyphosate-resistant (non-GR) soybean accumulated much higher shikimate than glyphosate-resistant (GR) soybean. Although some leguminous species were found to be more resistant to glyphosate than others, and there was considerable variation between species in the glyphosate to AMPA levels found, metabolism of glyphosate to AMPA did not appear to be a common factor in explaining natural resistance levels.     

Functional and Nutritional Characteristics of Wheat Grown in Organic and Conventional Cropping Systems

The effects of organic versus conventional farming practices on wheat functional and nutritional characteristics were compared. Soft white winter wheat and hard red spring wheat were obtained from multiyear replicated field plots near Pullman, Washington, and Bozeman, Montana. Test weight, kernel weight, and kernel diameter tended to be greater in both soft and hard organic wheat than in conventional wheat in the Pullman studies. Phenolic content and total antioxidant capacity tended to be lower in organic than in conventional wheat. Flour ash, P, and Mg contents in whole wheat flour varied in parallel among cropping systems, but levels were not consistently associated with either organic or conventional cropping systems. Protein contents of whole wheat and refined flours were similar in organic and conventional wheat from Pullman when fertility levels were similar. Higher fertility was associated with higher protein content in both organic and conventional cropping systems. Soft wheat flour from a low‐fertility organic cropping system had lower sodium carbonate, lactic acid, and sucrose solvent retention capacities, lower protein content, and greater cookie diameter and cake volume than soft wheat flour from the higher fertility organic and conventional cropping systems; the change in end‐product quality was significant in one out of two crop years. In the Bozeman hard wheat studies, higher fertility in both organic and conventional cropping systems tended to increase protein content and bread loaf volume. Results indicated that neither organic nor conventional cropping systems were associated with substantially improved mineral and antioxidant nutritional properties, and end‐use quality of wheat was more strongly associated with fertility level than with organic versus conventional cropping systems.     

Evaluation of spectrophotometric and HPLC methods for shikimic acid determination in plants: models in glyphosate-resistant and -susceptible crops

Endogenous shikimic acid determinations are routinely used to assess the efficacy of glyphosate in plants. Numerous analytical methods exist in the public domain for the detection of shikimic acid, yet the most commonly cited comprise spectrophotometric and high-pressure liquid chromatography (HPLC) methods. This paper compares an HPLC and two spectrophotometric methods (Spec 1 and Spec 2) and assesses the effectiveness in the detection of shikimic acid in the tissues of glyphosate-treated plants. Furthermore, the study evaluates the versatility of two acid-based shikimic acid extraction methods and assesses the longevity of plant extract samples under different storage conditions. Finally, Spec 1 and Spec 2 are further characterized with respect to (1) the capacity to discern between shikimic acid and chemically related alicyclic hydroxy acids, (2) the stability of the chromophore (t1/2), (3) the detection limits, and (4) the cost and simplicity of undertaking the analytical procedure. Overall, spectrophotometric methods were more cost-effective and simpler to execute yet provided a narrower detection limit compared to HPLC. All three methods were specific to shikimic acid and detected the compound in the tissues of glyphosate-susceptible crops, increasing exponentially in concentration within 24 h of glyphosate application and plateauing at approximately 72 h. Spec 1 estimated more shikimic acid in identical plant extract samples compared to Spec 2 and, likewise, HPLC detection was more effective than spectrophotometric determinations. Given the unprecedented global adoption of glyphosate-resistant crops and concomitant use of glyphosate, an effective and accurate assessment of glyphosate efficacy is important. Endogenous shikimic acid determinations are instrumental in corroborating the efficacy of glyphosate and therefore have numerous applications in herbicide research and related areas of science as well as resolving many commercial issues as a consequence of glyphosate utilization.     

Effect of Gaseous Acetic Acid Treatment on Breadmaking Properties of Flour

Eleven different wheat flours of varying protein content were treated with gaseous acetic acid. Each wheat flour exhibited maximum breadmaking properties (bread height and specific volume) at different levels of gaseous acetic acid treatment. There was a relationship (r = +0.7384) between the level of gaseous acetic acid treatment required for maximum breadmaking properties and the protein content of the wheat flour. Wheat flours with higher protein contents were more resistant to the decrease in pH value due to acetic acid treatment.     

Effects of Ferulic Acid and Transglutaminase on Hard Wheat Flour Dough and Bread

The effects of ferulic acid and transglutaminase (TG) on the properties of wheat flour dough and bread were investigated. Ferulic acid and TG were blended with hard wheat flour at levels of 250 and 2,000 ppm of flour weight, respectively. The addition of ferulic acid reduced the mixing time and mixing tolerance. The addition of TG did not obviously affect the mixing properties. Significant effects of ferulic acid plus TG on the rested dough texture were observed for overmixed dough. The maximum resistance (Rmax) of the dough was significantly reduced with the addition of ferulic acid but increased with the addition of TG. The addition of TG with ferulic acid restored the Rmax reduced by ferulic acid alone. The proportion of SDS‐soluble high molecular weight proteins in the dough increased with the addition of ferulic acid and decreased with TG, when assessed with size‐exclusion HPLC fractionation. Although the addition of TG improved the handling properties of the dough made sticky with added ferulic acid, it did not improve the quality of the bread with added ferulic acid as measured by loaf volume and firmness.     

Characteristics of French Bread Baked from Wheat Flours of Reduced Starch Amylose Content

Wheat genotypes of wild type, partial waxy, and waxy starch were used to determine the influence of starch amylose content on French bread making quality of wheat flour. Starch amylose content and protein content of flours were 25.0–25.4% and 14.3–16.9% for wild type; 21.2 and 14.9% for single null partial waxy; 15.4–17.1% and 13.2–17.6% for double null partial waxy; and 1.8 and 19.3% for waxy starch, respectively. Wheat flours of double null partial waxy starch produced smaller or comparable loaf volume of bread than wheat flours of wild type and single null partial waxy starch. Waxy wheat flour, despite its high protein content, generally produced smaller volume of bread with highly porous, glutinous, and weak crumb than wheat flours of wild type and partial waxy starch. French bread baked from a flour of double null partial waxy starch using the sponge-and-dough method maintained greater crumb moisture content for 24 hr and softer crumb texture for 48 hr of storage compared with bread baked from a flour of wild type starch. In French bread baked using the straight-dough method, double null partial waxy wheat flours with protein content >14.3% exhibited comparable or greater moisture content of bread crumb during 48 hr of storage than wheat flours of wild type starch. While the crumb firmness of bread stored for 48 hr was >11.4 N in wheat flours of wild type starch, it was <10.6 N in single or double null partial waxy flours. Wheat flours of reduced starch amylose content could be desirable for production of French bread with better retained crumb moisture and softness during storage.     

The composition of grain and forage from glyphosate tolerant wheat MON 71800 is equivalent to that of conventional wheat (Triticum aestivum L.)

Glyphosate tolerant wheat MON 71800, simply referred to as MON 71800, contains a 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) protein from Agrobacterium sp. strain CP4 (CP4 EPSPS) that has a reduced affinity for glyphosate as compared to the endogenous plant EPSPS enzyme. The purpose of this work was to evaluate the compositional equivalence of MON 71800 to its nontransgenic parent as well as to conventional wheat varieties. The compositional assessment evaluated the levels of proximates, amino acids, fatty acids, minerals, vitamins, secondary metabolites, and antinutrients in wheat forage and grain grown during two field seasons across a total of eight sites in the United States and Canada. These data demonstrated that with respect to these important nutritional components, the forage and grain from MON 71800 were equivalent to those of its nontransgenic parent and commercial wheat varieties. These data, together with the previously established safety of the CP4 EPSPS protein, support the conclusion that glyphosate tolerant wheat MON 71800 is as safe and nutritious as commercial wheat varieties.     

Variations in Amino Acid and Protein Contents of Wheat During Milling and Northern‐Style Steamed Breadmaking

To determine the variations of amino acid and protein during milling and steamed breadmaking, two types of wheat cultivars belonging to soft and hard wheat types were used. The results showed that losses occurred in 17 amino acids during milling. The mean loss of threonine (18.0%) was the highest, which was followed by proline (15.5%), methionine (15.1%), and histidine (15.1%). The losses of tyrosine and lysine were the lowest (8.1 and 9.7%, respectively). Losses were also found for 17 amino acids during steamed breadmaking. The highest loss was observed in alanine (17.1%), with tyrosine (12.5%) close behind, and leucine (4.3%) exhibiting the lowest loss. The mean protein contents for whole‐wheat meal, flour, and steamed bread prepared from the test materials were 15.25, 14.27, and 14.33%, respectively. This meant that protein content decreased during milling; however, a slight increase was observed during steamed breadmaking. Amino acid scores of lysine in whole‐wheat meal, flour, and steamed bread prepared from the test materials were 45.4, 41.0, and 38.2, respectively. The general trend in the variations of protein and amino acids was similar in the two wheat cultivars tested.     

Foliar-applied glyphosate substantially reduced uptake and transport of iron and manganese in sunflower (Helianthus annuus L.) plants

Evidence clearly shows that cationic micronutrients in spray solutions reduce the herbicidal effectiveness of glyphosate for weed control due to the formation of metal-glyphosate complexes. The formation of these glyphosate-metal complexes in plant tissue may also impair micronutrient nutrition of nontarget plants when exposed to glyphosate drift or glyphosate residues in soil. In the present study, the effects of simulated glyphosate drift on plant growth and uptake, translocation, and accumulation (tissue concentration) of iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu) were investigated in sunflower (Helianthus annuus L.) plants grown in nutrient solution under controlled environmental conditions. Glyphosate was sprayed on plant shoots at different rates between 1.25 and 6.0% of the recommended dosage (i.e., 0.39 and 1.89 mM glyphosate isopropylamine salt). Glyphosate applications significantly decreased root and shoot dry matter production and chlorophyll concentrations of young leaves and shoot tips. The basal parts of the youngest leaves and shoot tips were severely chlorotic. These effects became apparent within 48 h after the glyphosate spray. Glyphosate also caused substantial decreases in leaf concentration of Fe and Mn while the concentration of Zn and Cu was less affected. In short-term uptake experiments with radiolabeled Fe (59Fe), Mn (54Mn), and Zn (65Zn), root uptake of 59Fe and 54Mn was significantly reduced in 12 and 24 h after application of 6% of the recommended dosage of glyphosate, respectively. Glyphosate resulted in almost complete inhibition of root-to-shoot translocation of 59Fe within 12 h and 54Mn within 24 h after application. These results suggest that glyphosate residues or drift may result in severe impairments in Fe and Mn nutrition of nontarget plants, possibly due to the formation of poorly soluble glyphosate-metal complexes in plant tissues and/or rhizosphere interactions.     

Bran Characteristics and Bread‐Baking Quality of Whole Grain Wheat Flour

Variations in physical and compositional bran characteristics among different sources and classes of wheat and their association with bread‐baking quality of whole grain wheat flour (WWF) were investigated with bran obtained from Quadrumat milling of 12 U.S. wheat varieties and Bühler milling of six Korean wheat varieties. Bran was characterized for composition including protein, fat, ash, dietary fiber, phenolics, and phytate. U.S. soft and club wheat brans were lower in insoluble dietary fiber (IDF) and phytate content (40.7–44.7% and 10.3–17.1 mg of phytate/g of bran, respectively) compared with U.S. hard wheat bran (46.0–51.3% and 16.5–22.2 mg of phytate/g of bran, respectively). Bran of various wheat varieties was blended with a hard red spring wheat flour at a ratio of 1:4 to prepare WWFs for determination of dough properties and bread‐baking quality. WWFs with U.S. hard wheat bran generally exhibited higher dough water absorption and longer dough mixing time, and they produced smaller loaf volume of bread than WWFs of U.S. soft and club wheat bran. WWFs of two U.S. hard wheat varieties (ID3735 and Scarlet) produced much smaller loaves of bread (<573 mL) than those of other U.S. hard wheat varieties (>625 mL). IDF content, phytate content, and water retention capacity of bran exhibited significant relationships with loaf volume of WWF bread, whereas no relationship was observed between protein content of bran and loaf volume of bread. It appears that U.S. soft and club wheat bran, probably owing to relatively low IDF and phytate contents, has smaller negative effects on mixing properties of WWF dough and loaf volume of bread than U.S. hard wheat bran.     

干旱及复水条件下草甘膦对抗草甘膦大豆幼苗渗透调节物质和莽草酸含量的影响

为探明干旱胁迫及复水条件下不同剂量草甘膦对抗草甘膦大豆(RR1)幼苗叶片渗透调节物质、莽草酸(shikimic acid, SA)含量及根系活力的影响,采用盆栽试验,在大豆的第3复叶期进行水分胁迫5d和除草剂草甘膦处理,研究RR1幼苗叶片可溶性蛋白(soluble protein, SP)、可溶性糖(soluble sugar, SS)、游离脯氨酸(free praline, FP)、莽草酸(shikimic acid, SA)含量和根系活力(RA)的变化。结果表明,干旱胁迫前期RR1叶片的SP含量随草甘膦剂量的增加呈先升高后降低趋势,0.46kg/hm2叶片SP的含量最高,胁迫后期SP含量随草甘膦剂量的增加而降低;SS、FP和SA含量随草甘膦剂量的增加和胁迫时间的延长而增加,RA随草甘膦剂量的增加和胁迫时间的延长而降低。复水12d后,不同剂量草甘膦处理的各指标均有所恢复。干旱条件下,经草甘膦处理的RR1叶片的SP含量和RA低于草甘膦在正常水分条件下的处理,而SS、FP和SA含量相反。相关性分析表明,FP和SA含量与草甘膦剂量的相关关系最明显;而SS和SA含量与干旱胁迫时间的相关关系最明显。说明正常水分条件下,草甘膦对RR1幼苗造成的伤害经过一段时间后有所缓解;干旱胁迫加剧了草甘膦对RR1幼苗叶片渗透调节物质、莽草酸含量和根系活力的影响。抗草甘膦大豆主要通过积累FP、SS和SA对草甘膦和干旱胁迫做出响应。     

Effect of Gaseous Acetic Acid on Dough Rheological and Breadmaking Properties

Breads baked from wheat flours (protein contents 14.1–16.5% at 14.0% mb) that were pretreated with 2–3 mL of gaseous acetic acid per kg of wheat flour, showed maximum bread height and specific volume (cm³/g). Flour-water suspension and the crumb pH values were gradually decreased with increased amounts of acetic acid. Gas generation and dough expansion tests with bread dough showed that the addition of the same amount of acetic acid, which achieved maximum specific volume, also showed the highest rate of gas generation and dough expansion. However, increasing acetic acid decreased these values. Scanning electron microscope (Cryo-SEM) observation showed that the bread dough made from the same acetic acid-treated flour indicated continuum and no cracks in the dough matrix. Evaluation of mixograms showed the decrease of mixing stability with increased acetic acid levels. Viscosity and water binding capacity of flour-water suspensions were sharply increased by the addition of acetic acid at pH 5.0–3.5.     

Contribution of Sourdough Lactobacilli,Yeast, and Cereal Enzymes to the Generation of Amino Acids in Dough Relevant for Bread Flavor

The amino acid release was determined in wheat doughs supplied with salt, acid, dithiothreitol, or starter cultures to evaluate the relevance of the amino acid concentration on bread flavor. Wheat flour proteinases almost linearly released amino acids and the highest activity of wheat flour proteinases was found in acidified and reduced doughs. The effects of starter cultures on amino acid concentrations depended on their composition. Yeasts exhibited a high demand for amino acids, however, the total amino acid concentrations were not markedly affected by lactic acid bacteria. The individual amino acid contents were determined by the pH during fermentation and microbial metabolism. The formation of proline was favored by values higher than pH 5.5, whereas release of phenylalanine, leucine and cysteine mainly occurred at lower pH. Ornithine was found only in doughs fermented with Lactobacillus pontis. To determine effects of the amino acid concentration on bread aroma, fermented doughs were evaluated in baking experiments. An increased intensity of bread flavor was obtained by preferments prepared with lactic acid bacteria. The roasty note of wheat bread crust could be markedly enhanced by L. pontis. This results support the assumption that flavor of wheat bread is enhanced by increasing the concentration of free amino acids and especially ornithine in dough.     

Iron-Enriched Bread with Karkade (Hibiscus sabdariffa) and Wheat Flour

Karkade (Hibiscus sabdariffa) was blended with wheat flour to make bread. When 0.5% Karkade was blended with wheat flour, maximum bread height and specific volume (cm³/g) were obtained (pH 4.8–5.0); these properties gradually deteriorated with increased Karkade. The pH of the bread crumb decreased with increased Karkade, reaching pH 3.35 when blended with 10% Karkade. The pH of Karkade alone was 2.5, which was adjusted to ≈5.0 by the addition of alkali just before blending with wheat flour and making bread. Control of the Karkade pH resulted in bread height and specific volume recovering to the original optimal levels. In addition, the deep reddish purple color (513 nm) of the bread crumb changed to a brownish color crumb. The Fe content was 0.14 mg of Fe/gram of dry crumb, or 6.22 mg of Fe/60 g of fresh bread when 5% Karkade was blended with wheat flour.     

Influence of Soil Moisture on Root Colonization of Glyphosate‐Treated Soybean by Fusarium Species

Abstract

The widespread use of glyphosate‐resistant (GR) cropping systems may impact rhizosphere microbial associations and crop productivity. It was previously reported that glyphosate accumulation in the rhizosphere may stimulate colonization of soybean [Glycine max (L.) Merr.] roots by soilborne Fusarium. Field studies often reveal inconsistent root colonization by Fusarium, especially during growing seasons characterized by contrasting rainfall patterns. Therefore, this study was conducted to determine the impact of different soil moisture contents on root colonization of glyphosate‐treated soybean by Fusarium species. Glyphosate (0.84 kg ae ha^?1) was applied to greenhouse‐grown glyphosate‐resistant (GR) soybean at the two to three trifoliate-leaf (V2–V3) growth stage growing in a Mexico silt loam at 27%, 13%, and 10% soil moisture contents. Soil and plant samples were sampled periodically after herbicide application and selectively cultured for Fusarium. Highest Fusarium colonization was associated with the glyphosate treatment, with maximum levels occurring at the highest soil moisture level. Thus, glyphosate interactions with root colonization by Fusarium in glyphosate‐resistant soybean are greatly influenced by soil moisture content.     

Glyphosate-resistant and -susceptible soybean (Glycine max) and canola (Brassica napus) dose response and metabolism relationships with glyphosate

Experiments were conducted to determine (1) dose response of glyphosate-resistant (GR) and -susceptible (non-GR) soybean [Glycine max (L.) Merr.] and canola (Brassica napus L.) to glyphosate, (2) if differential metabolism of glyphosate to aminomethyl phosphonic acid (AMPA) is the underlying mechanism for differential resistance to glyphosate among GR soybean varieties, and (3) the extent of metabolism of glyphosate to AMPA in GR canola and to correlate metabolism to injury from AMPA. GR50 (glyphosate dose required to cause a 50% reduction in plant dry weight) values for GR (Asgrow 4603RR) and non-GR (HBKC 5025) soybean were 22.8 kg ae ha-1 and 0.47 kg ha-1, respectively, with GR soybean exhibiting a 49-fold level of resistance to glyphosate as compared to non-GR soybean. Differential reduction in chlorophyll by glyphosate was observed between GR soybean varieties, but there were no differences in shoot fresh weight reduction. No significant differences were found between GR varieties in metabolism of glyphosate to AMPA, and in shikimate levels. These results indicate that GR soybean varieties were able to outgrow the initial injury from glyphosate, which was previously caused at least in part by AMPA. GR50 values for GR (Hyola 514RR) and non-GR (Hyola 440) canola were 14.1 and 0.30 kg ha-1, respectively, with GR canola exhibiting a 47-fold level of resistance to glyphosate when compared to non-GR canola. Glyphosate did not cause reduction in chlorophyll content and shoot fresh weight in GR canola, unlike GR soybean. Less glyphosate (per unit leaf weight) was recovered in glyphosate-treated GR canola as compared to glyphosate-treated GR soybean. External application of AMPA caused similar injury in both GR and non-GR canola. The presence of a bacterial glyphosate oxidoreductase gene in GR canola contributes to breakdown of glyphosate to AMPA. However, the AMPA from glyphosate breakdown could have been metabolized to nonphytotoxic metabolites before causing injury to GR canola. Injury in GR and non-GR canola from exogenous application of AMPA was similar.