Norflurazon Research Articles

COR15B expression is affected by chloroplast functionality and its role in response to salt stress in Arabidopsis thaliana

Cold-responsive (COR) genes participate in the response of plants to low-temperature stress. In this study, we isolated and characterized a cold-responsive and light-inducible gene COR15B from Arabidopsis thaliana. Chloroplast damage caused by mutations (albino mutants seca1, secy1, and tic20) or by a norflurazon (NF) treatment resulted in a reduction of COR15B transcription. A semi-quantitative RT-PCR analysis shows that COR15B was induced by the salt stress in an abscisic acid-dependent manner. An over-expression of COR15B in Arabidopsis resulted in transgenic lines more sensitive to the NaCl treatment than the wild type. However, COR15B knockdown did not significantly affect the sensitivity of the cor15b mutant to the salt stress. Furthermore, we found that the expression of COR15A, a homologous gene of COR15B, was significantly elevated in cor15b mutant plants. All these results suggest that plants acquire the ability to fully express COR15B only after development of functional chloroplasts. The expressional reprogramming and functional backup may exist between COR15 homologues in Arabidopsis.

1O2-Mediated and EXECUTER-Dependent Retrograde Plastid-to-Nucleus Signaling in Norflurazon-Treated Seedlings of Arabidopsis thaliana

Chloroplast development depends on the synthesis and import of a large number of nuclear-encoded proteins. The synthesis of some of these proteins is affected by the functional state of the plastid via a process known as retrograde signaling. Retrograde plastid-to-nucleus signaling has been often characterized in seedlings of Arabidopsis thaliana exposed to norflurazon (NF), an inhibitor of carotenoid biosynthesis. Results of this work suggested that, throughout seedling development, a factor is released from the plastid to the cytoplasm that indicates a perturbation of plastid homeostasis and represses nuclear genes required for normal chloroplast development. The identity of this factor is still under debate. Reactive oxygen species (ROS) were among the candidates discussed as possible retrograde signals in NF-treated plants. In the present work, this proposed role of ROS has been analyzed. In seedlings grown from the very beginning in the presence of NF, ROS-dependent signaling was not detectable, whereas, in seedlings first exposed to NF after light-dependent chloroplast formation had been completed, enhanced ROS production occurred and, among others, (1)O2-mediated and EXECUTER-dependent retrograde signaling was induced. Hence, depending on the developmental stage at which plants are exposed to NF, different retrograde signaling pathways may be activated, some of which are also active in non-treated plants under light stress.

Control of Carotenoid Gene Expression in Bixa orellana L. Leaves Treated with Norflurazon

Bixa orellana (annatto or lipstick tree) is a perennial tropical plant that stores and produces considerable quantities of the apocarotenoid bixin, a culturally and economically important pigment used worldwide. However, the mechanisms underlying the gene regulation and pigment accumulation of bixin and carotenoids in annatto remain unknown. Bixin is present in the different tissues of the plant, although this pigment is primarily accumulated in the seed coat. Thus, the leaves are useful organs for understanding carotenoid and bixin production, thereby facilitating the study of this pigment, which would otherwise be difficult in ligneous adult plants. To study the regulation of bixin synthesis and to determine which genes are important regulatory molecules at the transcription level, the herbicide norflurazon (NF) was used to block carotenoid synthesis and bixin concentrations in B. orellana leaves. The genes activated in the early stages of the carotenoid pathway are involved in lycopene production (dxs, psy and pds), and those induced in the later stages of the carotenoid pathway, such as β and e-lycopene cyclases and boccd1, were differentially expressed compared with the control. The expression of some genes was more susceptible to certain concentrations of NF, potentially reflecting the roles of these genes in carotenoid synthesis in B. orellana. These results suggest that apocarotenoids, such as bixin, are synthesized using alternative precursors through the actions of genes that have not yet been identified.

Characterization of the first tuber mustard calmodulin-like gene, BjAAR1, and its functions in responses to abiotic stress and abscisic acid in Arabidopsis

The first tuber mustard calmodulin-like (CML) gene BjAAR1 (Brassica juncea var. tumida Tsen et Lee Abiotic stress and Abscisic acid (ABA) Responsive gene 1) was cloned and characterized. The protein encoded by BjAAR1 contains four predicted Ca2+ binding sites (EF-hand motif) and its recombinant protein can bind Ca2+ in vitro. qRT-PCR showed that the expression level of BjAAR1 was rather high in non-swollen stem of tuber mustard and largely reduced in swollen stem. Expression of BjAAR1 enhanced ABA- and stress-induced gene expression in Arabidopsis (Arabidopsis thaliana). Transgenic plants also exhibited hypersensitivity to NaCl, mannitol, and ABA during the seed germination and post-germination stages. ABA biosynthesis inhibitor, norflurazon (NF), rescued hypersensitivity phenotype of transgenic plants to NaCl and mannitol, indicating that BjAAR1 functions in multiple abiotic stresses response through ABA-dependent process.

Adsorption of diuron, fluridone and norflurazon on single-walled and multi-walled carbon nanotubes

The sorption behaviors of diuron (DIU), fluridone (FLU) and norflurazon (NOR) by a single-walled carbon nanotube (SWCNT) and three multi-walled carbon nanotubes (MWCNT) samples including MWCNT10 (<10nm, outer diameter), MWCNT20 (10–20nm), and MWCNT40 (20–40nm) were investigated. All adsorption isotherms were nonlinear and were well fitted with the Freundlich model and Dubinin Ashtakhov (DA) model. The linear relationships between the organic carbon (OC)-normalized saturated adsorption capacity (Q0OC) and surface area (SA) suggest that SA is presumably responsible for the adsorption of DIU and NOR on CNTs. While FLU, DIU, and NOR OC-normalized distribution coefficients (logKOC) of CNTs increased with increasing their hydrophobicity (logKOW) and the positive relationships between the logKOW-normalized logKOC (i.e., logKOC/logKOW) of FLU, DIU, and NOR and their hydrogen bonding ability indicate that the adsorption of FLU, DIU and NOR was mainly controlled by the hydrophobic interaction and hydrogen bonding. The higher logKOC or Q0OC values of MWCNT10 and SWCNT relative to other large MWCNTs and carbonaceous adsorbents suggest that MWCNT10 has the potential to serve as an adsorbent used to reduce the mobility of herbicides in agricultural and environmental applications.

Plastid-signalling-mediated anthocyanin accumulation in mature Arabidopsis rosettes

Genetic and physiological studies have revealed evidences for multiple signaling pathways by which the plastid exerts retrograde control over photosynthesis-associated-nuclear-genes (PhANGs). Recently, more and more studies showed that plastid signals affected more cellular processes other than PhANGs repression. Previous reports indicated that the herbicide norflurazon (NF)-derived signals, sugar signals and plastid gene expression (PGE)-derived signals all regulated anthocyanin accumulation and early anthocyanin biosynthesis gene expression in newly-germinated seedlings. In the research, we found that these signals also work as well for anthocyanin biosynthesis genes in mature Arabidopsis seedlings. Sugar/PGE signals doubled leaf total anthocyanins within 48 h (accumulated at the base of petiole), while NF signals induced a little anthocyanin accumulation (about 30 % and invisible to the naked eye). The plastid hexokinase (pHXK) participates in sugar/PGE signalling, while the plastid Genomes uncoupled protein 1 (GUN1) and the nuclear ABA-insensitive transcription factor 4 (ABI4) are involved in both sugar/PGE signalling and NF-derived signalling.

Assessment of herbicide sorption by biochars and organic matter associated with soil and sediment

Sorption of two herbicides, fluridone (FLUN) and norflurazon (NORO), by two types of biochars, whole sediment, and various soil/sediment organic matter (OM) fractions including nonhydrolyzable carbon (NHC), black carbon (BC) and humic acid (HA) was examined. The single-point organic carbon (OC)-normalized distribution coefficients (KOC) of FLUN and NORO at low solution concentration (Ce=0.01SW, solubility) for HA, NHC, and BC were about 3, 14, and 24 times and 3, 16, and 36 times larger than their bulk sediments, respectively, indicating the importance of different OM fractions in herbicide sorption. This study revealed that aliphatic moieties of the hydrothermal biochars and aromatic moieties of NHC samples, respectively, were possibly responsible for herbicide sorption. The hydrothermal biochar and condensed OM (i.e., NHC and BC) showed relatively high or similar herbicide sorption efficiency compared to the thermal biochar, suggesting that the hydrothermal biochar may serve as an amendment for minimizing off-site herbicide movement.

A highly efficient rice green tissue protoplast system for transient gene expression and studying light/chloroplast-related processes

BackgroundPlant protoplasts, a proven physiological and versatile cell system, are widely used in high-throughput analysis and functional characterization of genes. Green protoplasts have been successfully used in investigations of plant signal transduction pathways related to hormones, metabolites and environmental challenges. In rice, protoplasts are commonly prepared from suspension cultured cells or etiolated seedlings, but only a few studies have explored the use of protoplasts from rice green tissue.ResultsHere, we report a simplified method for isolating protoplasts from normally cultivated young rice green tissue without the need for unnecessary chemicals and a vacuum device. Transfections of the generated protoplasts with plasmids of a wide range of sizes (4.5-13 kb) and co-transfections with multiple plasmids achieved impressively high efficiencies and allowed evaluations by 1) protein immunoblotting analysis, 2) subcellular localization assays, and 3) protein-protein interaction analysis by bimolecular fluorescence complementation (BiFC) and firefly luciferase complementation (FLC). Importantly, the rice green tissue protoplasts were photosynthetically active and sensitive to the retrograde plastid signaling inducer norflurazon (NF). Transient expression of the GFP-tagged light-related transcription factor OsGLK1 markedly upregulated transcript levels of the endogeneous photosynthetic genes OsLhcb1, OsLhcp, GADPH and RbcS, which were reduced to some extent by NF treatment in the rice green tissue protoplasts.ConclusionsWe show here a simplified and highly efficient transient gene expression system using photosynthetically active rice green tissue protoplasts and its broad applications in protein immunoblot, localization and protein-protein interaction assays. These rice green tissue protoplasts will be particularly useful in studies of light/chloroplast-related processes.

Sorption of fluorinated herbicides to plant biomass-derived biochars as a function of molecular structure

Biochars produced at different heat treatment temperatures (HTT) are molecularly distinct and thus expected to show variable sorbent characteristics. We investigated the difference in sorption behavior of norflurazon (NORO) and fluridone (FLUN) to biochars from wood and grass feedstocks produced at different HTT. Amorphous biochars (HTT=400°C) exhibited the highest sorption parameter (KOC) for the two herbicides, emphasizing the importance of amorphous structural arrangement of aromatic moieties in these chars. Negative correlation between biochar aromaticity and isotherm nonlinearity (n) suggests that the n values were related mainly to total aromatic C content, not to that in the individual phases. Sorption of FLUN and NORO to low-temperature biochars (HTT=400°C) was about 1100 times and 6400 times greater, respectively, than a sediment sample, confirming that applications of low-temperature biochars to arable soils may reduce the mobility of FLUN and NORO, thus preventing unwanted herbicide leaching and subsequent contamination of sensitive water bodies.

Heme synthesis by plastid ferrochelatase I regulates nuclear gene expression in plants.

Chloroplast signals regulate hundreds of nuclear genes during development and in response to stress, but little is known of the signals or signal transduction mechanisms of plastid-to-nucleus (retrograde) signaling. In Arabidopsis thaliana, genetic studies using norflurazon (NF), an inhibitor of carotenoid biosynthesis, have identified five GUN (genomes uncoupled) genes, implicating the tetrapyrrole pathway as a source of a retrograde signal. Loss of function of any of these GUN genes leads to increased expression of photosynthesis-associated nuclear genes (PhANGs) when chloroplast development has been blocked by NF. Here we present a new Arabidopsis gain-of-function mutant, gun6-1D, with a similar phenotype. The gun6-1D mutant overexpresses the conserved plastid ferrochelatase 1 (FC1, heme synthase). Genetic and biochemical experiments demonstrate that increased flux through the heme branch of the plastid tetrapyrrole biosynthetic pathway increases PhANG expression. The second conserved plant ferrochelatase, FC2, colocalizes with FC1, but FC2 activity is unable to increase PhANG expression in undeveloped plastids. These data suggest a model in which heme, specifically produced by FC1, may be used as a retrograde signal to coordinate PhANG expression with chloroplast development.

Transient accumulation of Mg-protoporphyrin IX regulates expression of PhANGs – New evidence for the signaling role of tetrapyrroles in mature Arabidopsis plants

Genetic and physiological studies have revealed evidence for multiple signaling pathways by which the plastid exerts retrograde control over photosynthesis associated nuclear genes (PhANGs). It has been proposed that the tetrapyrrole pathway intermediate Mg-protoporphyrin IX (Mg-proto IX) acts as the signaling molecule in the pathways and accumulates in the chloroplasts and cytosol of the cell after treatment with the herbicide Norflurazon (NF). However, the role of Mg-Proto IX in plastid signaling has been challenged by two recent reports. In this paper, new evidence is presented supporting Mg-Proto IX as a plastid-signaling molecule in mature Arabidopsis seedlings. Fluorescence HPLC and confocal microscope observation verified that a short-term (<96 h) NF treatment resulted in a large accumulation of Mg-Proto IX accompanying with Lhcb repression, whereas the long-term NF treatments caused marked changes of tetrapyrrole pools, while Lhcb expression was continuously repressed. These results may explain the discrepancies among different reports. Reactive oxygen species (ROS) eliminator treatments only partly reversed the NF-induced repression of Lhcb. Therefore, the NF generates both ROS signals and Mg-Proto IX signals. Furthermore, our data suggested that plastid signal transduction through plastid GUN1 protein is independent of tetrapyrrole export from the plastid.

‘happy on norflurazon’ (hon) mutations implicate perturbance of plastid homeostasis with activating stress acclimatization and changing nuclear gene expression in norflurazon‐treated seedlings

Various mutant screens have been undertaken to identify constituents involved in the transmission of signals from the plastid to the nucleus. Many of these screens have been performed using carotenoid-deficient plants grown in the presence of norflurazon (NF), an inhibitor of phytoene desaturase. NF-treated plants are bleached and suppress the expression of nuclear genes encoding chloroplast proteins. Several genomes uncoupled (gun) mutants have been isolated that de-repress the expression of these nuclear genes. In the present study, a genetic screen has been established that circumvents severe photo-oxidative stress in NF-treated plants. Under these modified screening conditions, happy on norflurazon (hon) mutants have been identified that, like gun mutants, de-repress expression of the Lhcb gene, encoding a light-harvesting chlorophyll protein, but, in contrast to wild-type and gun mutants, are green in the presence of NF. hon mutations disturb plastid protein homeostasis, thereby activating plastid signaling and inducing stress acclimatization. Rather than defining constituents of a retrograde signaling pathway specifically associated with the NF-induced suppression of nuclear gene expression, as proposed for gun, hon mutations affect Lhcb expression more indirectly prior to initiation of plastid signaling in NF-treated seedlings. They pre-condition seedlings by inducing stress acclimatization, thereby attenuating the impact of a subsequent NF treatment.

Production of [13C]‐lycopene from high lycopene tomato cell suspension cultures

The goal of this work was to use tomato cell suspension cultures treated with enzyme inhibitors and grown with [13C6]‐glucose as a carbon source to produce labeled carotenoids (CAR) for human metabolism research. To promote CAR accumulation, the high lycopene (LYC) tomato cell suspension line ‘Ailsa Craig’ hp‐1 was grown with carotenogenic enzyme inhibitors norflurazon (NORF), 2‐(4‐chlorophenyl‐thio) triethylamine (CPTA), both herbicides (BOTH), or neither (CONT). Significantly greater combined CAR [phytoene (PE), phytofluene (PF), and LYC] yields were obtained with the NORF, CPTA, and BOTH treatments (5.2 ± 0.7, 3.6 ± 0.4, 4.2 ± 0.4 mg/L, respectively) than CONT (0.3 ± 0.1 mg/L). Different PE, PF, and LYC profiles were obtained where CPTA led to 0.26 ± 0.02, 0.14 ± 0.02, and 3.18 ± 0.45 mg/L; NORF led to 4.96 ± 0.68, 0.20 ± 0.06, and 0.06 ± 0.02 mg/L; BOTH led to 2.98 ± 0.14, 0.18 ± 0.05, and 1.05 ± 0.36 mg/L; CONT led to 0.18 ± 0.09, 0.02 ± 0.00, and 0.06 ± 0.01 mg/L, respectively. To biolabel LYC the hp‐1 cell line was grown in medium containing 30 g/L [13C6]‐glucose and CPTA. LYC, PE, and PF yields from labeled cultures were 2.5 ± 0.1, 0.3 ± 0.0, 0.1 ± 0.0 mg/L, respectively. Mass isotopomer distribution analysis for LYC [13C]‐enrichment from a pilot labeling run was performed using LC‐MS/MS, and 82% of the LYC molecules had at least 34 of 40 carbons labeled, and the greatest percent (17%) was uniformly labeled. (NIH/NCI CA 112649‐01A1)

In‐depth analysis of the distinctive effects of norflurazon implies that tetrapyrrole biosynthesis, organellar gene expression and ABA cooperate in the GUN‐type of plastid signalling

Application of norflurazon (NF) damages plastids, induces photobleaching and represses expression of the nuclear LHCB1.2 gene encoding a light-harvesting protein. In genomes uncoupled (gun) mutants, LHCB1.2 expression is maintained in the presence of NF. The mutants gun2, gun4 and gun5 exhibit perturbations in tetrapyrrole biosynthesis, but gun1 is defective in organellar gene expression (OGE). How gun mutations affect nuclear gene expression (NGE) and why the signals elicited by the two types evoke the same response remains unknown. Here we show that the carotenoid biosynthesis inhibitors amitrole and flurochloridone can replace NF in gun assays, whereas novel tetrapyrrole pathway mutations do not provoke a gun phenotype. Changes in haem levels also do not account for LHCB1.2 derepression in NF-treated gun mutants. Pigment measurements indicated that gun mutants are not resistant to NF, but gun2, gun4 and gun5 retain low levels of lutein, as well as of neoxanthin and violaxanthin, the precursors of abscisic acid (ABA). This might explain the enhanced ABA sensitivity of gun4 and gun5 plants found in germination assays. Metabolite profiling and analyses of reactive oxygen species and cellular redox state failed to suggest a link between gun mutations and altered LHCB1.2 expression. However, in contrast to NF-treated wild-type plants, gun mutants retain to a marked extent the capability to express the plastome-encoded proteins AtpB and RbcL. This, together with the finding that application of ABA can partially restore LHCB1.2 expression in NF-treated wild-type plants, supports the view that tetrapyrrole, OGE and ABA signalling are interconnected.

Tetrapyrrole profiling in Arabidopsis seedlings reveals that retrograde plastid nuclear signaling is not due to Mg-protoporphyrin IX accumulation

Chloroplast biogenesis involves careful coordination of both plastid and nuclear gene expression, which is achieved in part by retrograde signaling from the chloroplast to the nucleus. This can be demonstrated by the fact that the herbicide, Norflurazon (NF), which causes bleaching of chloroplasts, prevents the light induction of photosynthesis-related genes in the nucleus. It has been proposed that the tetrapyrrole pathway intermediate Mg-protoporphyrin IX acts as the signaling molecule in this pathway and accumulates in the chloroplasts and cytosol of the cell after NF treatment. Here we present data that demonstrate that this model is too simplistic. We have developed a sensitive liquid chromatography-mass spectrometry (LC/MS) method to measure tetrapyrrole intermediates and have shown that no Mg-protoporphyrin IX, nor indeed any other chlorophyll-biosynthesis intermediate, can be detected in NF-treated plants under conditions in which nuclear gene expression is repressed. Conversely when endogenous Mg-protoporphyrin IX levels are artificially increased by supplementation with the tetrapyrrole precursor, 5-aminolevulinic acid, the expression of nuclear-encoded photosynthetic genes is induced, not repressed. We also demonstrate that NF-treatment leads to a strong down-regulation of tetrapyrrole biosynthesis genes, consistent with the absence of an accumulation of tetrapyrrole intermediates. Finally, there is no correlation between nuclear-gene expression and any of the chlorophyll biosynthetic intermediates over a range of growth conditions and treatments. Instead, it is possible that a perturbation of tetrapyrrole synthesis may lead to localized ROS production or an altered redox state of the plastid, which could mediate retrograde signaling.

Production of distinct carotenoid mixtures from tomato cell suspension cultures varies by herbicide treatment and variety used.

Tomato product consumption has been correlated with decreased chronic disease risk. Radiolabeled forms of tomato carotenoids are essential for tracking bioavailability, biodistribution, and metabolism in human and animal models; however, many of these compounds are not commercially available. In order to target specific compounds and efficiently produce mixtures of tomato carotenoids [phytoene (PE), phytofluene (PF), and lycopene (LYC)] for future radiolabeling, different herbicide treatments and tomato cell lines were investigated. Three herbicide treatments [norflurazon (NORF), 2‐(4‐chlorophenyl‐thio) triethylamine (CPTA), or NORF &amp; CPTA (COMBO)] were investigated with ‘VFNT Cherry’. CPTA treatment yielded primarily LYC (2.49 mg/L culture) followed by PE &amp; PF (0.30, 0.32 mg/L). NORF treatment yielded the greatest PE (1.00 mg/L) followed by PF (0.10 mg/L) and traces of LYC. COMBO treatment led to the best‐mixed yields of PE, PF, and LYC (1.09, 0.28, 1.45 mg/L). Five different cell lines (‘VFNT Cherry’, ‘Ailsa Craig’ hp‐1, ‘Ailsa Craig’ WT, ‘Manapal’ hp‐2, and ‘Manapal’ WT) were treated with CPTA and evaluated, and ‘VFNT Cherry’ and the ‘Ailsa Craig’ hp‐1 mutant accumulated the greatest LYC. Selected varieties and herbicide treatments will be applied for radiolabeled carotenoid generation for use in future animal and human trials. (Supported by NIH/NCI CA 112649‐01A1)

Effect of various cyclodextrins on photodegradation of a hydrophobic herbicide in aqueous suspensions of different soil colloidal components

This paper investigated the photochemical behaviour of the herbicide norflurazon (NFL) in the presence of different soil colloidal components and several cyclodextrins (CDs). The interaction of NFL with CDs yielded the formation of inclusion complexes at 1:1 stoichiometric ratio in solution, with an increase of the herbicide solubility. The irradiation of NFL aqueous solutions in the presence of CDs showed that the higher the formation constant of NFL–CD complexes ( K c) and their solubility, the higher their photocatalytic effects, following the CDs in the order: RAMEB > HPBCD > β-CD > α-CD > γ-CD. The presence of the different soil colloidal components in aqueous suspension provoked the reduction of the NFL photodegradation rate, due to a screening effect, especially when goethite and humic acids were present. No disappearance of NFL was detected in parallel studies carried out in the dark, except in the case of humic acids, where a 5% adsorption of the initial amount of NFL was adsorbed in the dark control. The presence of the different CDs in such systems showed an inductive photodegradation effect on the herbicide. This could be largely explained by the inclusion effects of CDs in catalyzing interactions between NFL and certain reactive radicals generated by the different colloidal components. Although this work was carried out at laboratory scale and therefore, has limited applications, it reveals that cyclodextrins increase solubilization of hydrophobic herbicides and could lead to their increased photodegradation. This could be a promising method for pesticide-contaminated water remediation. However, it is important to consider the effect of the soil colloidal components in the different aquatic systems and their concentrations, since they can alter the photodegradative effects of the cyclodextrins.

Differential antioxidant responses in catalase-deficient maize mutants exposed to norflurazon

Maize catalase (CAT) mutants lacking in CAT isozymes were used to investigate the response of CAT and superoxide dismutase (SOD) to norflurazon (NF) caused oxidative stress in 18-d post-pollination scutella. NF treatment caused an increase in malonyldialdehyde content, which is an indicator of oxidative stress, and a decrease in a content of photoprotectant carotenoids in the scutella. CAT activity decreased greatly with increasing NF concentration in standard maize line (W64A) and CAT-2 null mutant (WA10C), however, it remained relatively constant in CAT-2/CAT-3 double null mutant (WDN10). Cat1 transcript increased in the NF-treated scutella of W64A and WDN10, with a greater Cat1 transcript in WDN10, whereas Cat2 transcript decreased in the NF-treated scutella of all lines examined. In all lines, SOD activities were not changed noticeably at various NF concentrations. In the scutella of W64A, Sod4A decreased in response to NF but the other Sod transcript contents were unchanged. The CAT-deficient mutants reacted with raised transcripts of Sod1, Sod3, Sod4 or Sod4A.

Time-dependent sorption of norflurazon in four different soils: Use of β-cyclodextrin solutions for remediation of pesticide-contaminated soils

High pesticide concentrations in soil from spills or discharges can result in point-source contamination of ground and surface waters. Cost-effective technologies are needed for on-site treatment that meet clean-up goals and restore soil function. Remediation is particularly challenging when a mixture of pesticides is present. β-Cyclodextrins (BCD) solutions are employed to enhance the aqueous solubility of a hydrophobic organic compound. The interaction of norflurazon (NFL) with BCD yielded the formation of inclusion complexes at a 1:1 stoichiometric ratio in solution. The change of the sorption parameter K d as affected by the time, and desorption studies of NFL previously adsorbed on four different soils with different characteristics have been performed in the presence of 0.01 M BCD or 0.01 M Ca(NO 3) 2 acting as extractant solutions. NFL sorption increased with the residence time in soil, making it more resistant to be desorbed. Likewise, leaching experiments were performed in packed soil columns eluting initially with distilled water, with the aim to simulate the herbicide drainflow losses because of rainfall, approaching to a more realistic environment, and later with 0.01 M BCD solutions to extract the residual NFL bound. The results showed that removal efficiencies of the different flushing systems were significantly influenced by their affinity and selectivity for the contaminants in the soil matrix as well as BCD adsorption on soils, since this could act like a bridge between pesticide molecule and soil particles increasing the stay of NFL in soil. These results are further information to be in condition to predict the potential effect of the BCD solutions on soil chemical decontamination in the field situation assessing the likelihood for bioremediation of a pesticide contaminated-soil, since the increasing in hydrosolubility of the contaminants means the first step before microorganism uptaken.

Effect of the Simultaneous Addition of β-Cyclodextrin and the Herbicide Norflurazon on Its Adsorption and Movement in Soils

The effects of beta-cyclodextrin (BCD) on the sorption-desorption and transport processes of the herbicide norflurazon (NFL) in soils of different characteristics when both are applied simultaneously have been investigated. Adsorption-desorption studies of NFL on six soils of very different characteristics in the presence of BCD have been performed using a batch equilibration method and correlated to its mobility in homogeneous hand-packed soil columns. NFL determinations were undertaken by HPLC equipped with a diode array detector at a wavelength of 220 nm. BCD was also analyzed by HPLC with fluorimetric detection using a postcolumn reaction. The interaction of NFL with BCD yielded the formation of an inclusion complex in solution. When this complex is applied to soils, a large decrease in NFL adsorption capacity and an increase in its desorption were observed, due to the higher tendency of NFL-BCD complexes to remain in solution. The results obtained in adsorption and soil column experiments indicated that the influence of BCD on NFL mobility and availability depends on the different affinities of BCD to be sorbed on soils of different characteristics and on the concentration of BCD used. The lower the concentration of BCD added, the more tenaciously it adheres to the soil, and most of the BCD molecules would be adsorbed, providing a coating to soil particles that acts as a bridge between NFL and the soil surface, acting as an adsorbent and retarding the mobility of the herbicide. At higher concentrations of BCD, or in soils where its adsorption is very low, most of the BCD molecules are in the aqueous phase and NFL molecules tend to be complexed with BCD in solution, acting then as a solubilizing agent.