The use of genetically modified or native microorganisms and plants to degrade or remove pollutants has emerged as a powerful technology for in situ remediation. An understanding of the genetic basis of the mechanisms of how microorganisms and plants biodegrade pollutants and how they interact with the environment is important for successful implementation of this technology. Recent studies have demonstrated that microbes and transgenic plants produce pesticide-degradaing enzymes that can mineralize different groups of pesticides and their metabolites with greater efficiency. This review describes the most recent progress in biotechnological approaches for enhancing the capability of microorganisms and plants through the characterization and transfer of pesticide-degrading genes, induction of catabolic pathways, and display of cell surface enzymes.

Bioremediation and Phytoremediation of Pesticides: Recent Advances

�SUMMARY As photosynthesis is the basic process during which light energy is absorbed and converted into organic matter, the importance of the plant pigment chlorophyll (a and b forms) as an intermediary in transformation of the absorbed solar energy and its activity in the process of photosynthesis and synthesis of organic substances in plants are crucial Therefore, this paper provides an overview of methods for monitoring the optical activity of chlorophyll molecules and methods (non-destructive and destructive) for quantification of chlorophyll in plants These methods are used to estimate the effects of different stress factors (abiotic, biotic and xenobiotic) on the efficiency of photosynthesis and bioproductivity, aiming to assess the impact that these limiting factors have on the yield of various cultivars Also, those methods for analysis of chlorophyll optical activity and/or content are appropriate for assessing the reaction of weed species to different agricultural practices (mineral nutrition, treatment by herbicides, etc) and studies of different aspects of weed ecophysiology and their influence on crop harvest

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Chlorophyll as a measure of plant health: agroecological aspects.

Fomesafen, saflufenacil, and sulfentrazone had similar parameters for their mass spectrometry analysis, all being analyzed in negative mode with similar ionization energies. Flumioxazin was analyzed in positive mode using different ionization temperatures and voltage energies, and a larger injection volume (10 µl compared with 2–5 µl) due to lower liquid chromatography–mass spectrometry (LC-MS) detector response. Quantitative limits of detection in soil were < 5 parts per billion by weight for all herbicides. The field study was conducted three times (2010, 2011, 2012) with four blocks of each treatment each year. Herbicide concentrations over time were based on field samples that were later extracted and quantified using the described LC-MS procedures. Data were examined using a simple first-order (SFO) equation with each year-by-herbicide treatment combination regressed using SigmaPlot version 12.5 to determine regression parameters. The SFO rate constant was used to determine a half life, or D...

https://bioone.org/journals/weed-science/volume-62/issue-4/WS-D-13-00183.1/Dissipation-of-Fomesafen-Saflufenacil-Sulfentrazone-and-Flumioxazin-from-a-Tennessee/10.1614/WS-D-13-00183.1.pdf

Dissipation of Fomesafen, Saflufenacil, Sulfentrazone, and Flumioxazin from a Tennessee Soil under Field Conditions

Pesticide-contaminated fields can be found worldwide due to excessive use of insecticides, herbicides and fungicides. Many of the pesticides that were once used intensively are now forbidden and have been shown to have deleterious health effects. Plants, bacteria and fungi have been shown to possess pesticide-degrading capacities, which can be applied in the successful remediation of contaminated fields and water. This article will first provide an overview of the different types of pesticides, their application and their key characteristics, followed by an analysis of their behaviour in the environment. Pesticides that are introduced into the environment seldom stay where they were applied. A complex system of transport, transfer and transformation of pesticides throughout different environmental compartments often takes place. These processes all influence the possible remediation of the pesticide-contaminated media. We will then review several possible remediation strategies that are currently available. Bioremediation is the first technology that is reviewed. With bioremediation, the focus is on the remediation of pesticides by microorganisms in bulk soil, without the aid or presence of plants. Second, plant-associated remediation is discussed. When focussing on plant-associated remediation, a distinction has to be made between rhizoremediation in the rhizosphere and phytoremediation within the plant tissues. While rhizoremediation and phytoremediation processes are possible solely with the use of plants, many of these processes are optimized by associations between plants and microorganisms. Plants and bacteria or fungi often live in a symbiotic relationship that aids them in surviving contaminated environments, as well as with the degradation of the contaminants they encounter. In the last part of the review, we discuss the advantages and disadvantages of “natural” remediation strategies as compared to more classical industrial approaches.

Bio- and Phytoremediation of Pesticide-Contaminated Environments: A Review

Effectiveness of glyphosate and imazamox on the control of the invasive cordgrass Spartina densiflora.

Flumioxazin is an herbicide registered for use in soybean and peanut. However, few published papers concerning the soil persistence of flumioxazin are available. Therefore, laboratory studies were initiated to determine the half-life (t(1/2)) of flumioxazin in Greenville sandy clay loam and Tifton loamy sand soils when incubated at 15 and 25 degrees C. Results indicated that temperature had little effect on flumioxazin persistence. The t(1/2) for the Greenville soil was 17.9 and 16.0 days while the Tifton soil was 13.6 and 12.9 days, at 15 and 25 degrees C, respectively. These data correspond to the greater clay content of the Greenville soil (32%) as compared to the Tifton soil (2%). Therefore, the Greenville soil had greater soil adsorption and less flumioxazin was generally available to be degraded by soil microorganisms. In soils that were heat treated to reduce microbe populations, 99% of initial flumioxazin was accounted for after 16 days. Mineralization of flumioxazin, measured as 14CO2 evolution, was also greater in the Tifton soil (2.2% after 64 days) than in the Greenville soil (2.0% after 64 days). From these data, it was concluded that microbes were the most influential factor concerning the degradation of flumioxazin.

Flumioxazin soil persistence and mineralization in laboratory experiments.

Sulfentrazone is a herbicide that has been observed to injure crops in an unpredictable manner. Therefore, experiments were conducted to determine whether root absorption of sulfentrazone was dependent on the pH of the rooting medium. Studies were initiated to examine sulfentrazone uptake of whole plants from soil and hydroponic solution, as well of excised roots in solution. These experiments demonstrated that transpiration decreased as soil pH decreased and herbicide rate increased; it was our intention to use this measure as a description of herbicide injury. Likewise, plants grown for 24 h in 14C-sulfentrazone hydroponic solution accumulated a greater herbicide concentration in roots as solution pH decreased below 6.5. This trend of increased absorption with reduced solution pH was again demonstrated when excised cotton roots were placed for durations of 10 to 120 min in hydroponic solution containing 14C-sulfentrazone. However, when excised roots were placed in solution containing the weak a...

Sulfentrazone absorption by plant roots increases as soil or solution pH decreases

Experiments were initiated to determine the amount of time required for postemergence herbicides to render yellow nutsedge physiologically noncompetitive. The rate of net CO2 assimilation (AN) was chosen as the response variable to describe competitiveness. Specifically, the time required after herbicide treatment for AN to drop to 50% of that of the untreated control (AN50) was determined. AN50 values for halosulfuron, imazapic, glyphosate, and MSMA were 1.6, 2.1, 3.2, and 3.3 d, respectively. An AN50 value was not calculated for bentazon because AN rapidly decreased below 50% but recovered to > 50% by 9 d after treatment (DAT). Stomatal conductance to water vapor (gs) declined similarly with AN over time for halosulfuron, imazapic, and glyphosate treatments. However, gs of MSMA-treated plants was near 95% of the untreated control, whereas AN declined to 35% 11 DAT. At 11 DAT, all aboveground biomass was removed, and plants were returned to the greenhouse, and regrowth was determined after an ad...

Duration of yellow nutsedge (Cyperus esculentus) competitiveness after herbicide treatment

Greenhouse studies were initiated to determine the duration of time after herbicide treatment required to render johnsongrass physiologically noncompetitive. Nicosulfuron, imazapic, clethodim, and glyphosate were applied to rhizomatous johnsongrass at 35, 70, 140, and 840 g ai ha−1, respectively. Net carbon assimilation, stomatal conductance, chlorophyll meter readings, and maximum (dark adapted) efficiency of photosystem II were measured. Net carbon assimilation (AN) was assumed to be the best indicator of johnsongrass competitiveness. Johnsongrass was considered to be physiologically noncompetitive when AN declined below 50% of that of nontreated check. From these data, it was concluded that glyphosate rendered johnsongrass noncompetitive most readily, 4.3 d after treatment, whereas no differences were detected between nicosulfuron, imazapic, or clethodim throughout the experiment. Stomatal conductance (gs) was highly correlated to AN and was determined to be an adequate substitute for AN when ...

The effect of selected herbicides on CO2 assimilation, chlorophyll fluorescence, and stomatal conductance in johnsongrass (Sorghum halepense L)

Three herbicides were compared for their ability to reduce both carbon fixation and soil water depletion by yellow nutsedge in a growth chamber study. Whole-plant CO2 exchange and water use were measured for 11 d after herbicide application. MSMA reduced carbon assimilation relative to the untreated control 1 d after treatment, and by 5 d after treatment respiration exceeded carbon assimilation during the photoperiod; however, MSMA had no significant effect on whole-plant water use during the measurement period. Halosulfuron reduced gross carbon assimilation to 30% of the pretreatment rate by the end of the experiment, but in contrast to MSMA it also strongly suppressed water use. Mesotrione never reduced carbon assimilation below 59% of the pretreatment rate and had no measurable effect on water use. Halosulfuron and MSMA reduced shoot regrowth to between 0 and 5% of the control, whereas mesotrione treatment allowed some 58% regrowth. These results indicate that whereas both MSMA and halosulfuro...

Jason A. Ferrell

Papers

Flumioxazin soil persistence and mineralization in laboratory experiments.

Sulfentrazone absorption by plant roots increases as soil or solution pH decreases

Duration of yellow nutsedge (Cyperus esculentus) competitiveness after herbicide treatment

The effect of selected herbicides on CO2 assimilation, chlorophyll fluorescence, and stomatal conductance in johnsongrass (Sorghum halepense L)

Effects of three herbicides on whole-plant carbon fixation and water use by yellow nutsedge (Cyperus esculentus)