Herbicide Clomazone Research Articles

Effect of herbicide clomazone on photosynthetic processes in primary barley ( Hordeum vulgare L.) leaves

The effect of pre-emergently applied herbicide clomazone on the photosynthetic apparatus of primary barley leaves ( Hordeum vulgare L.) was studied. Clomazone application caused a reduction in chlorophyll ( a+ b) and carotenoid levels that was accompanied by a decline in the content of light harvesting complexes as judged from the increasing chlorophyll a/ b ratio. The pigment reduction also resulted in changes in 77 K chlorophyll fluorescence emission spectra indicating lower chlorophyll (Chl) fluorescence reabsorption and absence of the long-wavelength emission forms of photosystem I. The maximal photochemical yield of photosystem II (PSII) and the reoxidation kinetics of the primary quinone acceptor Q A − were not significantly influenced by clomazone. A higher initial slope of Chl fluorescence rise in the Chl fluorescence induction kinetic indicated an increased delivery of excitations to PSII. Simultaneously, analysis of the Chl fluorescence quenching revealed that clomazone reduced function of the electron transport chain behind PSII. The decrease in the saturation rates of CO 2 assimilation paralleled the decrease of the Chl content and has been suggested to be caused by a suppressed number of the electron transport chains in the thylakoid membranes or by their decreased functionality. The obtained results are discussed in view of physiological similarity of the clomazone effect with changes of photosynthetic apparatus during photoadaptation.

Monitoring of the herbicide clomazone in environmental water samples by solid-phase extraction and high-performance liquid chromatography with ultraviolet detection

Evaluation of a simple and rapid method for determination of clomazone in environmental water samples, by high-performance liquid chromatography with ultraviolet detection, is described. After solid-phase extraction with C18 extraction cartridges clomazone was separated on a C18 column with 65∶35 (v/v) methanol-water, pH 4.0, as mobile phase at a flow-rate of 1.0 mL min−1. After optimization of the extraction and separation conditions, the method was used for determination of clomazone residues in rivers and agricultural waters of the central region of the Rio Grande do Sul province. The results revealed that clomazone persists in agricultural water at least for 130 days, and was present in 90% of the river water samples analyzed.

Response of Several Transplanted Pepper Cultivars to Variable Rates and Methods of Application of Clomazone

Field studies were conducted to evaluate the tolerance of several pepper (Capsicum annuum L.) cultivars to the herbicide clomazone. Peppers tested included the bell cultivars Yolo Wonder and Jupiter; the banana cultivar Sweet Banana; and the pungent cultivars Jalapeno and Red Chili. Treatments were clomazone at 0.56 or 1.12 kg·ha-1 a.i. applied either preplant incorporated (PPI), pretransplant (PRE-T), or posttransplant (POS-T) on the day of transplanting, plus a nontreated control. Clomazone at 1.12 kg·ha-1 a.i. PPI and PRE-T significantly injured (bleaching or chlorosis of foliage) `Sweet Banana' (40% and 20%, respectively) and `Red Chili' (30% and 18%, respectively) in 1993 in early-season evaluations, but this injury was transient and did not significantly affect total fruit number or yield. Injury to any cultivar from POS-T clomazone at 0.56 and 1.12 kg·ha-1 a.i. was nonsignificant. Overall, tolerance to clomazone was excellent for all treatments and across all cultivars. Yield was not reduced significantly by any treatment. Chemical names used: 2-[(2-chlorophenyl) methyl]-4, 4-dimethyl-3-isoxazolidinone (clomazone).

Properties and inhibition of the first two enzymes of the non-mevalonate pathway of isoprenoid biosynthesis

Enzymes of the 1-deoxy-D-xylulose 5-phosphate/2-C-methylerythritol 4-phosphate (DOXP/MEP) pathway are targets for new herbicides and antibacterial drugs. Until now, no inhibitors for the DOXP synthase have been known of. We show that one of the breakdown products of the herbicide clomazone affects the DOXP synthase. One inhibitor of the non-mevalonate pathway, fosmidomycin, blocks the DOXP reductoisomerase (DXR) of plants and bacteria. The I(50) values of plants are, however, higher than those found for the DXR of Escherichia coli. The DXR of plants, isolated from barley seedlings, shows a pH optimum of 8.1, which is typical for enzymes active in the chloroplast stroma.

Factors controlling degradation of pesticides in soil

Rates of pesticide degradation in soil exhibit a high degree of variability, the sources of which are usually unclear. Combining data from incubations performed using a range of soil properties and environmental conditions has resulted in greater understanding of factors controlling such degradation. The herbicides clomazone, flumetsulam, atrazine, and cloransulam-methyl, as well as the former insecticide naphthalene offer examples of degradation kinetics controlled by coupling competing processes which may in turn be regulated separately by environmental conditions and soil properties. The processes of degradation and volatilization appear to compete for clomazone in solution; sorbed clomazone is degraded only after the solution phase is depleted. Similarly, volatilization of naphthalene is enhanced when degradation has been inhibited by high nutrient levels. Degradation of the herbicide flumetsulam has been shown to be regulated by sorption, even though the compound has a relatively low affinity for the soil. The fate pathway for cloransulam-methyl shifts from mineralization to formation of metabolities, bound residues and physically occluded material as temperature increases. Atrazine degradation in soil may be controlled in part by the presence of inorganic nitrogen, as the herbicide appears to be used as a nitrogen source by micro-organisms. New insight gained from measurement of multiple fate processes is demonstrated by these examples.

Risk assessment of the herbicide Clomazone to aquatic life

Clomazone (2-(2-chlorophenyl)methyl-4.4-dimethyl-3-isoxazolidinone) is a post emergence herbicide widely used in rice fields in Rio Grande do Sul (Brazil) with high activity against Gramineae at the recommended application rate(AR).of 700g/ha. The herbicide input into the aquatic ecosystem may occur by aerial application or water drainage. The presence of this chemical in the water may affect non-target organisms leading to impairments in the aquatic food chain. Studies were conducted in this work to evaluate the risk of Clomazone using the estimated mean affective concentration (EC50) for the microalgae Selenastrum capricornutum(96h), the duckweed Lemna valdiviana(96h) and the crustacean Daphnia similis(48h). The EC50 values were 11.2; 31.7 and 13.8 mg/l, respectively. According to the obtained data, and considering a direct input of the herbicide in a 10cm column water, the estimated maximum application rate that doesn't cause acute effects is 5.3 AR for S. capricornutum, 6.5 AR for D. similis and 15.0 AR for L. valdiviana. The estimated maximum application rate that doesn't cause chronic effects is 2.0 AR for D. similis, 1.6 AR for S. capricornutum and 4.5 AR for L. valviana.

Microbial Transformations of Clomazone

Common soil fungi and bacteria were screened for their abilities to biotransform the herbicide clomazone (2-[(2-chlorophenyl)methyl]-4,4-dimethyl-3-isoxazolidinone) into metabolites. Preparative-scale incubations were conducted with Aspergillus niger (UI-X172) and Cunninghamella echinulata (NRRL-3655) to obtain metabolites in sufficient quantities for spectral and chromatographic identification. HPLC analyses were used to assess the capacities of 41 microorganisms to metabolize the herbicide. Based on comparisons with authentic standard compounds and on the structures of metabolites ascertained by 1H NMR and mass spectrometry, major microbial transformation reactions involved hydroxylation at the 5-methylene carbon of the isoxazolidone ring, hydroxylation of a methyl group on the oxazolidone ring, and aromatic hydroxylation at position 3‘. Minor metabolic routes included dihydroxylations of clomazone on the aromatic ring, cleavage of the isoxazolidone N−C bond, or complete removal of the isoxazolidone rin...

Growth kinetics of a Pseudomonas sp. in the presence of the herbicide Clomazone

Growth kinetics of a Pseudomonas sp. in the presence of the herbicide Clomazone

Influence of clomazone herbicide on postharvest quality of processing squash and pumpkin

Certain cultivars of processing pumpkins and squash, such as Golden Delicious and Butternut squash, are more sensitive to application of clomazone (Command herbicide) than others, resulting in paler coloration of fruit tissues-an undesirable condition for food processors. The objective of this research was to evaluate the influence of clomazone on fruit color retention over time in six processing squash and pumpkin cultivars that exhibited various degrees of clomazone sensitivity. Color retention was monitored by total carotenoid content after curing. Relative levels of fatty acids and peroxidase (POD) and lipoxygenase (LOX) enzyme activities, associated with membrane and pigment integrity in higher plants, were assayed. Total carotenoid content of treated tissue varied, with Golden Delicious and Butternut squash significantly affected by herbicide treatment. Treatments of clomazone resulted in increased POD activity in Turk's Turban and Buttercup squash. No difference was observed for LOX activity in treated or control samples.

Clomazone sorption in soil: Incubation time, temperature, and soil moisture effects.

Sorption-desorption of the herbicide clomazone in a silty clay loam soil was evaluated for time, temperature, and moisture dependence. In unsaturated soil, clomazone sorption peaked at different times depending on incubation temperature. Soil moisture had little effect on clomazone sorption. The apparent K d increased (2.4-fold at 5 °C and 4.1-fold at 35 °C) throughout the 84-day incubation period. Clomazone extractable with water in 15 min decreased with incubation time, while that recovered between 15 min and 24 h was essentially constant. Desorption kinetics were well characterized with a simple radial diffusion model by adjusting a single parameter (concentration of the labile pool). Batch equilibrium sorption isotherms (saturated soil) were temperature independent (5-35 °C). The data indicate that the time-dependent sorption of clomazone in unsaturated soil is controlled by a temperature-dependent process. Clomazone losses from solution explained much of the increase in apparent K d over time.

RESPONSE OF SWEETPOTATOES TO WINTER COVER CROPS

Rye, wheat, hairy vetch, ryegrass, and Austrian winterpea were evaluated for effects on weed control and sweetpotato production. Sweetpotatoes were transplanted into these cover crops after the cover crops had been killed with glyphosate and mowed. One-half of each plot was treated with clomazone herbicide and one-half was not treated. Plots with rye residues contained fewer goosegrass, rice flatsedge, ground cherry, and smooth pigweed plants than other cover crop plots. Sweetpotato plant vigor was greatest in the rye plots. Goosegrass, crabgrass, groundcherry, and eclipta were controlled in cover crop plots treated with clomazone. Sweetpotato plant vigor was better in the plots treated with clomazone than in plots with a cover crop only. Highest yields of no. 1 grade and total marketable sweetpotatoes were in rye and ryegrass cover crop plots, with or without clomazone. Sweetpotatoes grown in Austrian winterpea plots without clomazone produced the lowest yields. There was an increase in yield of sweetpotatoes in all cover crop plots treated with clomazone.

Metabolism of clomazone herbicide in soybean

The metabolism of 2-[(2-chlorophenyl) methyl]-4,4-dimethyl-3-isoxazolidinone (clomazone) was studied in soybean plants grown in the greenhouse using 14C-radiolabeled clomazone at 1.1 and 2.2 kg of ai/ha. Isolation and identification of clomazone metabolites from soybean plants at 30 and 60 days after treatment indicated that the major metabolic processes included dealkylation of the parent chemical at the alkylamide linkage and conjugation of the resulting chlorobenzyl moiety to form its corresponding glycoside(s). Other minor metabolic routes included monohydroxylation of clomazone on either the aromatic or the isoxazolidinone moieties with subsequent formation of their corresponding glycosides. Additional polar metabolites that may result either from extensive degradation or from amino acid conjugations of parent compound or its intermediate metabolites were also observed.

Herbicide Clomazone Does Not Inhibit In Vitro Geranylgeranyl Synthesis from Mevalonate

Clomazone reduced the chlorophyll and carotenoid contents of spinach (Spinacia oleracea L.), barley (Hordeum vulgare L.), velvetleaf (Abutilon theophrasti Medik.), and soybean (Glycine max L. Merr.) seedlings. The order of species sensitivity was velvetleaf > spinach > barley > soybean. Clomazone (100 micromolar) did not affect the in vitro activities of spinach isopentenyl pyrophosphate isomerase or prenyl transferase. Clomazone also did not affect the synthesis of isopentenyl pyrophosphate from mevalonic acid. Thus, clomazone had no direct in vitro effect on the synthesis of geranylgeranyl pyrophosphate from mevalonic acid. Greening seedlings of both soybean and velvetleaf metabolized clomazone. No qualitative differences in the metabolites were detected between soybean and velvetleaf. Thus, differential metabolism of clomazone to a toxic chemical that inhibits terpenoid synthesis is unlikely. Clomazone has either a mode of action not yet identified or a metabolite that is selective in that it is much more active in sensitive than tolerant species.

Pretreatment with bleaching herbicides alleviates the light-induced inhibition of maize 3-hydroxy-3-methylgutaryl-coenzyme A reductase activity

Etiolated seedlings of maize ( Zea mays L., var. ‘Dekalb XL72AA’) contain high levels of the enzyme 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR, EC 1.1.1.34).The influence of pretreatments with several herbicides known to interfere with plant isoprenoid synthesis on the light-induced inhibition of maize microsomal HMGR activity was examined. Pretreatment with the bleaching herbicides clomazone, norflurazon, fluridone, and acifluorfen (Na-salt) stimulated by four- to sevenfold the in vivo activity of microsomal HMGR extracted from 5-day-old maize seedlings grown in a 24-hr photoperiod with strong light (600 μmol/m 2/sec). Pretreatment with the growth-retarding herbicides EPTC and metolachlor did not affect the in vivo activity of microsomal HMGR extracted from maize seedlings grown under the same conditions. The in vivo activity of maize microsomal HMGR was not stimulated by any of the four bleaching herbicides when herbicide-treated maize seedlings were grown under continuous dark conditions. When herbicidetreated maize seedlings were germinated and grown in a 6-hr photoperiod with weak light (40 μmol/m 2/sec), the only herbicide that bleached maize seedlings and stimulated the in vivo activity of their microsomal HMGR was clomazone. None of the bleaching herbicides examined in this study exhibited any direct effects on the in vitro activity of microsomal HMGR extracted from etiolated maize seedlings. Mevinolin, a highly competitive inhibitor of HMGR, inhibited the in vitro activity of microsomal HMGR extracted from etiolated maize seedlings. These results suggest that the light-induced inhibition of maize microsomal HMGR activity may be indirect, resulting from the direct influence of light on chloroplast morphogenesis, a differentiation process disrupted by bleaching herbicides.

Clomazone Causes Accumulation of Sesquiterpenoids in Cotton (Gossypium hirsutumL.)

The herbicide clomazone caused ultrastructural damage to etioplasts of cotton cotyledons. Etioplast envelopes were irregular, prothylakoids were absent or irregular, stroma density was low, and there were abnormal stromal vesicles. Further damage occurred upon exposure to light. Clomazone greatly slowed the conversion of chlorophyllide to chlorophyll in cotton, suggesting that phytol synthesis was affected. Neither synthesis of protochlorophyllide nor phototransformation of protochlorophyllide to chlorophyllide was affected by clomazone. Clomazone completely inhibited carotenoid synthesis without an accumulation of phytoene. However, the sesquiterpenoids hemigossypol and the dimeric sesquiterpenoid gossypol accumulated in greater amounts in clomazone-treated than in control tissues. These results indicate that this herbicide inhibits synthesis of terpenoids after the formation of farnesyl pyrophosphate.

Development of an enzyme-linked immunosorbent assay for the detection of the herbicide clomazone

An enzyme-linked immunosorbent assay (ELISA) for clomazone, the active ingredient in the soybean herbicide Command, was developed. The ELISA system proved to be a fast, sensitive, and accurate method of clomazone detection. The assay was not affected by soil type; however, soil extracts did influence detection sensitivity. The assay was specific for clomazone and did not detect the soybean herbicides metribuzin, metolachlor, or trifluralin

Interactions of the Bleaching Herbicide Clomazone with Reduced Glutathione and Other Thiols

The reactivity of the bleaching herbicide clomazone with reduced glutathione (GSH) was studied under in vitro conditions. Clomazone at 1.3 mM and GSH at 100 mM were reacted in a phosphate buffer (pH 8.8) at 25 °C for 3 days. The resulting synthetic product was identified as a GS-conjugate of clomazone by means of TLC, HPLC, and mass spectrometry (chemical ionization) procedures. Exogenous application of 0.5 mM of GSH and cysteine reduced significantly the bleaching effect of clomazone on leaf disks of velvetleaf (Abutilon theophrasti Medik.). Mercaptoethanol was not effective in antagonizing the bleaching effect of clomazone on velvetleaf leaf disks. These results show that clomazone can react with selected thiol compounds under in vitro conditions. The conjugation of clomazone with GSH may be involved in the metabolic detoxication of this herbicide in plants.

Uptake and Metabolism of Clomazone in Tolerant-Soybean and Susceptible-Cotton Photomixotrophic Cell Suspension Cultures

Studies were conducted to determine the uptake and metabolism of the pigment synthesis inhibiting herbicide clomazone in tolerant-soybean (Glycine max [L.] Merr. cv Corsoy) and susceptible-cotton (Gossypium hirsutum [L.] cv Stoneville 825) photomixotrophic cell suspensions. Soybean and cotton on a whole plant level are tolerant and susceptible to clomazone, respectively. Preliminary studies indicated that I(50) values for growth, chlorophyll (Chl), beta-carotene, and lutein were, respectively, >22, 14, 19, and 23 times greater for the soybean cell line (SB-M) 8 days after treatment (DAT) compared to the cotton cell line (COT-M) 16 DAT. Differences in [(14)C]clomazone uptake cannot account for selectivity since there were significantly greater levels of clomazone absorbed by the SB-M cells compared to the COT-M cells for each treatment. The percentage of absorbed clomazone converted to more polar metabolite(s) was significantly greater by the SB-M cells relative to COT-M cells at 6 and 24 hours after treatment, however, only small differences existed between the cell lines by 48 hours after treatment. Nearly identical levels of parental clomazone was recovered from both cell lines for all treatments. A pooled metabolite fraction isolated from SB-M cells had no effect on the leaf pigment content of susceptible velvetleaf (Abutilon theophrasti Medic.) or soybean seedlings. Conversely, a pooled metabolite fraction from COT-M cells reduced the leaf Chl content of velvetleaf. Soybean tolerance to clomazone appears to be due to differential metabolism (bioactivation) and/or differences at the site of action.

Growth and physiological responses of normal, dwarf, and albino corn ( Zea mays) to clomazone treatments

The effects of the bleaching herbicide clomazone (2-[(2-chlorophenyl)methyl]-4,4-dimethyl-3-isoxazolidinone) on the growth of selected mutants of corn ( Zea mays L.) were evaluated. A normal hybrid (“Dekalb XL67”), a gibberellin-deficient dwarf-5 mutant, and a chlorophyll- and carotenoid-deficient albino ( lw 3 ) mutant of corn were exposed to clomazone applied preemergence at rates of 0.0, 0.3, 0.6, and 1.1 kg/ha under greenhouse conditions. Normal corn was very sensitive to clomazone treatments and was severely bleached. Shoot height, shoot dry weight, and chlorophyll content of normal corn were strongly inhibited by all application rates of clomazone. The effects of combined treatments of clomazone and the growth retardant CCC on the growth of normal corn were additive or synergistic. The clomazone induced retardation of the longitudinal growth of normal corn was reversed by exogenously applied gibberellin (GA 3). The dwarf-5 mutant exhibited a greater tolerance to clomazone than normal corn. Clomazone caused a slight chlorosis and reduced the longitudinal growth of this mutant only when applied at the highest rate of 1.1 kg/ha. The short-lived growth of the lethal albino mutant of corn was not affected significantly by clomazone. Normal and dwarf-5 corn responded quite differently when treated with the bleaching herbicide norflurazon. In contrast to the results obtained with clomazone, both normal and dwarf-5 corn were bleached severely by all rates of norflurazon but their shoot heights were not affected by this herbicide. Norflurazon reduced shoot dry weights of normal corn, but not of the dwarf-5 mutant. These results support previously published reports suggesting that clomazone acts by a new mechanism of bleaching action which is different than that of norflurazon. The lesser sensitivity of the gibberellin-deficient dwarf-5 mutant to clomazone and the reversal of clomazone-induced effects on normal corn by exogenous gibberellin suggest a secondary action of this herbicide on gibberellin biosynthesis.