Acropetal Translocation Research Articles

Uptake, Acropetal Translocation, and Enantioselectivity of Perfluorooctane Sulfonate in Maize Coexisting with Copper.

Plant uptake and translocation of perfluorooctane sulfonate (PFOS) are critical for food safety and raise major concerns. However, those processes are associated with many undisclosed mechanisms, especially when PFOS coexist with heavy metals. In this study, we investigated the effect of copper (Cu) on PFOS distribution in maize tissues by assessing the PFOS concentration and enantioselectivity. The presence of <100 μmol/L Cu exerted a limited effect on PFOS bioaccumulation, while >100 μmol/L Cu damaged the root cell membrane and increased root permeability, resulting in a higher PFOS concentration in roots. The suppression of acropetal translocation might be attributed to Cu inhibition of carrier proteins. The enantiomer fraction (EF) of 1m-PFOS at <100 μmol/L Cu was higher than that in a commercial product (0.5). Racemic PFOS was detected at >100 μmol/L Cu in roots and the EF variation changed from positive to negative in shoots. These EF results evidenced the existence of a protein-mediated uptake pathway. Besides, this study indicated the challenge of chiral signature application in PFOS source identification, given the effects of heavy metals and plants on PFOS enantioselectivity. The findings provide insight into PFOS bioaccumulation in plants cocontaminated with Cu and will facilitate environmental risk assessment.

Uptake and translocation of perfluoroalkyl acids with different carbon chain lengths (C2-C8) in wheat (Triticum acstivnm L.) under the effect of copper exposure.

The co-contamination by perfluoroalkyl acids (PFAAs) and heavy metals (HMs) is ubiquitous in the surface environment subjected to sewage irrigation and land application of sludge. However, the joint effects of HMs and PFAAs on plant roots are not well clarified. This study explored the root uptake and acropetal translocation behaviors of C2-C8 PFAAs by wheat (Triticum acstivnm L.) under the co-exposure of copper (Cu). The underlying uptake mechanisms of PFAAs were verified in a defective root system. The results showed that excessive Cu (100-400μmol/L) damaged the cell membrane of wheat root to increase electrolytic leakage. In the defective root system, the root concentrations of PFAAs decreased by 6%-73% and the decrease rates were negatively associated with the carbon chain length of PFAAs. Along with the decrease in root concentrations of PFAAs, the amount of ultrashort-chain (C2-C3) and short-chain (C4-C6) PFAAs translocated to the shoot also decreased by 45%-84%. In contrast, the acropetal translocation of long-chain (C8) PFAAs, perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), was enhanced under Cu exposure due to the increase in root permeability as observed by increased electrolytic leakage. The shoot concentrations of PFOA and PFOS under Cu exposure were up to 5.5 and 11 times higher than those in the control, respectively. These results suggested that PFOA and PFOS could enter wheat root more easily through the breaks caused by Cu exposure and thereby their acropetal transportation to shoot was enhanced. Therefore, the risk of plant accumulation of long-chain PFAAs can be potentially underestimated if without considering the co-contamination with HMs in the environment.

Interaction between Xanthomonas citri pv. viticola and its alternative natural host, Senna obtusifolia, and species in the family Amaranthaceae

Alternative hosts play an important role on the survival of plant pathogenic bacteria. They represent sources of inoculum for new infections; therefore, the identification of potential alternative hosts and the study of their interaction with plant pathogens are essential for the development of effective disease management strategies. The objective of this study was to investigate the interaction between Xanthomonas citri pv. viticola (Xcv), the grapevine bacterial canker (GBC) pathogen, and its alternative host, Senna obtusifolia, and species in the family Amaranthaceae (Amaranthus spinosus, A. cruentus, Chenopodium giganteum, and C. quinoa), for a better understanding of the host range of this pathogen and epidemiology of GBC. Pathogenicity tests showed that all species developed symptoms after inoculation of Xcv. The dynamics of the leaf population was evaluated up to 20 days after inoculation (DAI). In all plant species, it was observed an increase of the total population of Xcv after inoculation. Xcv also showed the ability to survive epiphytically in high populations in S. obtusifolia leaves, after 20 DAI. The ability to invade plant tissues systemically was evaluated by stem inoculation and subsequent detection by specific BIO-PCR. In S. obtusifolia, acropetal and basipetal movement was evaluated by collecting stem fragments at 1, 5, 10, and 15 cm from the inoculation site (IS) at 14 and 20 DAI. In Amaranthaceae plants, only the acropetal translocation was evaluated at 5 cm from IS at 21 DAI. Xcv movement in S. obtusifolia was detected in both directions, at 15 and 10 cm, above and below the IS, respectively. In plants of the family Amaranthaceae, the pathogen was detected in all tissue samples evaluated. The results indicated that Xcv colonized systemically all plant species evaluated and could potentially infect a wider host range than previously known.

Reducing phenanthrene uptake and translocation, and accumulation in the seeds by overexpressing OsNRT2.3b in rice

The uptake and accumulation of polycyclic aromatic hydrocarbons (PAHs) in crops have gained much attention due to their toxicity to humans. Nitrogen (N) is an essential element for plant growth and has also been implicated in the acquisition and acropetal translocation of PAHs. OsNRT2.3b encodes a nitrate (NO3−) transporter that is involved in the acquisition and mobilization of N in rice. Here, we investigated whether overexpression of OsNRT2.3b would exert any mitigating influence on the uptake and translocation of phenanthrene (Phe, a model PAH) in transgenic rice (Oryza sativa). The wild-type seedlings exhibited a reduction in plant height, primary root length, and shoot biomass when grown hydroponically in a medium supplemented with Phe. Acquisition of Phe by the roots and its subsequent translocation to shoots increased concomitantly with an increase in Phe concentration in the medium and duration of the treatment. OsNRT2.3b-overexpressing lines (Ox-6 and Ox-8) were generated independently. Compared with the wild-type, the concentration of Phe in Ox-6 and Ox-8 were significantly lower in the roots (47%–54%) and shoots (22%–31%) grown hydroponically with Phe (1 mg/L). Further, the wild-type and Ox lines were grown to maturity in a pot soil under Phe conditions and the concentrations of Phe and total N were assayed in the culms and flag leaves. Compared with the wild-type, in Ox lines the concentration of total N significantly increased in the culms (288%–366%) and flag leaves (12%–25%), while that of Phe significantly reduced in the culms (25%–28%) and flag leaves (18%–21%). The results revealed an antagonistic correlation between the concentration of total N and Phe. The concentration of Phe was also significantly lower (29%–38%) in the seeds of Ox lines than the wild-type. The study highlighted the efficacy of overexpressing OsNRT2.3b in mitigating the Phe toxicity by attenuating its acquisition, mobilization, and allocation to the seeds.

High Nitrogen and Phosphorous Acquisition by Belowground Parts of Caulerpa prolifera (Chlorophyta) Contribute to the Species' Rapid Spread in Ria Formosa Lagoon, Southern Portugal.

Despite worldwide proliferation of the genus Caulerpa and subsequent effects on benthic communities, little is known about the nutritional physiology of the Caulerpales. Here, we investigated the uptake rates of ammonium, nitrate, amino acids,and phosphate through the fronds and rhizoids+stolon, the internal translocation of nitrogen, and developed a nitrogen budget for the rapidly spreading Caulerpa prolifera in Ria Formosa lagoon, southern Portugal. Caulerpaprolifera acquired nutrients by both aboveground and belowground parts at similar rates, except nitrate, for which fronds showed 2-fold higher uptake rates. Ammonium was the preferential nitrogen source (81% of the total nitrogen acquisition), and amino acids, which accounted for a significant fraction of total N acquisition (19%), were taken up at faster rates than nitrate. Basipetal translocation of 15 N incorporated as ammonium was nearly 3-fold higher than acropetal translocation, whereas 15 N translocation as nitrate and amino acids was smaller but equal in either direction. The estimated total nitrogen acquisition by C.prolifera was 689 μmol · m-2 ·h-1 , whereas the total nitrogen requirement for growth was 672μmol·m-2 ·h-1 . The uptake of ammonium and amino acids by belowground parts accounted for the larger fraction of the total nitrogen acquisition of C.prolifera and is sufficient to satisfy the species nitrogen requirements for growth. This may be one reason explaining the fast spreading of the seaweed in the bare sediments of Ria Formosa where it does not have any macrophyte competitors and the concentration of nutrients is high.

Acropetal translocation of phenanthrene in wheat seedlings: Xylem or phloem pathway?

Due to the potential toxicity of polycyclic aromatic hydrocarbons (PAHs) to humans, the uptake and translocation of PAHs in food crops have gained much attention. However, it is still unclear whether phloem participates in the acropetal translocation of PAHs in plants. Herein, the evidence for acropetal translocation of phenanthrene (a model PAH) via phloem is firstly tested. Wheat (Triticum aestivum L.) new leaves contain significantly higher phenanthrene concentration than old leaves (P < 0.05), and the inhibitory effect on phenanthrene translocation is stronger in old leaves after abscisic acid and polyvinyl alcohol (two common transpiration inhibitors) application. Phenanthrene concentration in xylem sap is slightly higher than in phloem sap. Ring-girdling treatment can significantly reduce phenanthrene concentration in castor bean (Ricinus communis L.) leaves. Two-photon fluorescence microscope images indicate a xylem-to-phloem and acropetal phloem translocation of phenanthrene in castor bean stem. Therefore, phloem is involved in the acropetal translocation of phenanthrene in wheat seedlings, especially when the xylem is not mature enough in scattered vascular bundle plants. Our results provide a deeper understanding of PAH translocation in plants, which have significant implications for food safety and phytoremediation enhancement of PAH-contaminated soil and water.

Mixture toxicity and uptake of 1-butyl-3-methylimidazolium bromide and cadmium co-contaminants in water by perennial ryegrass (Lolium perenne L.)

Ionic liquids, a kind of emerging and persistent organic contaminants, always coexist with heavy metals in aquatic and terrestrial environments. However, the feasibility of phytoremediation to remove ionic liquids and heavy metals co-contaminants is still unclear. Thus, in this study, the hydroponic experiment was conducted to investigate the combined effect of 1-butyl-3-methylimidazolium bromide ([C4mim]+Br−) and cadmium (Cd2+) on growth and physiological indictors of perennial ryegrass, together with their uptake and translocation by plants. Results show that the exposure of ryegrass to [C4mim]+ and Cd2+ mixture significantly inhibited the biomass growth and affected the photosynthetic pigments contents in leaves. The increases of lipid peroxidation and catalase, peroxidase activity were also observed under the co-exposure experiments. The mixture toxicity of [C4mim]+ and Cd2+ to ryegrass growth showed an additive effect predicted by concentration addition and independent action. [C4mim]+ uptake and acropetal translocation by ryegrass were significantly inhibited with dosing Cd2+. In contrast, [C4mim]+ had no obvious effect on Cd2+ uptake by ryegrass, while enhanced Cd2+ translocation from roots to shoots occurred with increasing [C4mim]+ dosages. These results indicate that the co-contamination of ionic liquids and heavy metals would affect their fates during phytoremediation.

Uptake pathway and accumulation of polycyclic aromatic hydrocarbons in spinach affected by warming in enclosed soil/water-air-plant microcosms.

The partition of polycyclic aromatic hydrocarbons (PAHs) among water-soil-air is temperature-dependent. Thus, we hypothesized that climate warming will affect the accumulation and uptake pathway of PAHs in plants. To test this hypothesis, enclosed soil/water-air-plant microcosm experiments were conducted to investigate the impact of warming on the uptake and accumulation of four PAHs in spinach (Spinacia oleracea L.). The results showed that root uptake was the predominant pathway and its contribution increased with temperature due to the promoted acropetal translocation. Owing to the increase in freely dissolved concentrations of PAHs in soil pore water, the four PAH concentrations in roots increased by 60.8-111.5% when temperature elevated from 15/10 to 21/16 °C. A model was established to describe the relationship between bioconcentration factor of PAHs in root and temperature. Compared with 15/10 °C, the PAH concentrations in leaves at both 18/13 and 21/16 °C elevated due to the increase in PAH concentrations in air, while slightly decreased when temperature elevated from 18/13 to 21/16 °C because the PAH concentrations in air decreased, resulting from accelerated biodegradation of PAHs in topsoil. This study suggests that warming will generally enhance the PAH accumulation in plant, but the effect will differ among different plant tissues.

Nitrogen acquisition and resource allocation strategies in temperate seagrass Zostera nigricaulis: Uptake, assimilation and translocation processes

The dominant seagrass in Port Phillip Bay (PPB), Australia, Zostera nigricaulis, declined between 2000 and 2011, coinciding with the ‘Millennium drought’ that ended in 2009. These seagrasses are nitrogen-limited, underpinning the need to develop nitrogen budgets for better ecosystem management. Environmentally realistic measurements of specific uptake rates and resource allocation were undertaken to develop nitrogen budgets and test the hypothesis that the above-ground and below-ground compartments are able to re-mobilise ammonium and nitrate through uptake, translocation and assimilation to adapt to varying levels of nitrogen in the ecosystem. Uptake of 15N labelled ammonium and nitrate by above- and below-ground seagrass biomass, epiphytes and phytoplankton was quantified in chambers in situ. Preferential uptake of ammonium over nitrate was observed, where the uptake rate for nitrate was about one sixth of that for ammonium. Epiphytes and phytoplankton also registered an increased affinity for ammonium over nitrate. Translocation experiments demonstrated the uptake by both the above-ground and below-ground biomass, respectively from the water column and pore water, and subsequent translocation to the opposite compartment. Acropetal translocation (below- to above-ground biomass) was more prevalent than basipetal translocation. This is a unique outcome given basipetal translocation has been widely reported for Zostera by other researchers.

Rhizospheric effects on atrazine speciation and degradation in laterite soils of Pennisetum alopecuroides (L.) Spreng.

Atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine) is a worldwide-used herbicide and often detected in agricultural soils and groundwater at concentrations above the permitted limit, because of its high mobility, persistence, and massive application. This study applied pot experiments to investigate the atrazine contents and speciation during the phytoremediation process by Pennisetum alopecuroides (L.) Spreng. in laterite soils. From the change of the total atrazine and bioavailable atrazine measured by diffusive gradients in thin film (DGT), P. alopecuroides significantly improved atrazine degradation efficiency from 15.22 to 51.46%, attributing to the increasing bioavailable atrazine in rhizosphere. Only a small amount of atrazine was taken up by P. alopecuroides root and the acropetal translocation from roots to shoots was limited. The atrazine speciation was significantly different between rhizosphere and non-rhizosphere, attributing to the declining pH and organic matters in rhizosphere. The relationship between pH and soil-bound/humus-fixed atrazine illustrated the pH-dependant release of the atrazine from soils and the competition between humus adsorption and uptake by P. alopecuroides. The present study reveals the important roles of soil pH and organic matters in atrazine speciation and availability in laterite soils, and provides new insights in the rhizospheric effects on effective phytoremediation of atrazine.

Reflection of Stereoselectivity during the Uptake and Acropetal Translocation of Chiral PCBs in Plants in the Presence of Copper.

Plant uptake and acropetal translocation of polychlorinated biphenyls (PCBs) is a major concern, with many uncertainties, especially when plants are exposed to coexisting PCBs and metals. Studying atropisomer selectivity behavior is a well-proven method for identifying the biotransformation process of chiral PCBs in plants. This study investigated the uptake, translocation, and stereoselectivity of PCB95 and PCB136 (3 μg/L in hydroponics and 200 μg/kg in pot experiment) by monocot corn and dicot sunflower after copper (Cu) exposure (50 μmol/L in hydroponics and 400 mg/kg in pot experiment). Cu exposure led to significantly increased PCBs accumulation in roots and enhanced their acropetal translocation from roots to shoots, attributed to Cu-induced root damage. In the absence of Cu, the first-eluting enantiomer of PCB95 and second-eluting enantiomer of PCB136 were preferentially enriched in the shoots and roots of both the monocot and the dicot, and the enantioselectivity of chiral PCBs was more pronounced in shoots than in roots. Cu exposure significantly reduced the stereoselectivity of PCB95 and PCB136 in the defective root system, implying that PCB95 and PCB136 uptake into roots after Cu exposure changed from active biotransformation to passive diffusion. Our findings suggest that the ecological risk of PCB95 and PCB136 uptake and accumulation in plants is underestimated at sites cocontaminated with metals and PCBs and, for the first time, reveal the mechanism associated with the uptake and biotransformation of chiral PCBs in plants after exposure to both heavy metals and chiral PCBs.

Uptake and translocation of polycyclic aromatic hydrocarbons (PAHs) and heavy metals by maize from soil irrigated with wastewater

By investigating the uptake of 16 priority polycyclic aromatic hydrocarbons (PAHs) and five heavy metals from soils to maize at the farmlands with industrial wastewater irrigation, this study revealed the effects of heavy metals on PAHs uptake in terms of co-contamination. The results of 15 investigated soils showed medium contamination level and the vertical PAHs distribution in soils indicated that 2–3 rings PAHs with low octanol-water partition coefficient (log Kow < 4.5) were easier to transport in soils, causing a great potential risk immigrating to the groundwater. The 3-ring PAHs were most likely to be taken up by maize roots whereas 2- and 4–6 ring PAHs had the lower likelihood. The translocation of PAHs in maize tissues has positive relationship with log Kow less than 4.5, while negatively correlated otherwise. Redundancy analysis indicated the unexpected results that, except for soil PAHs concentration, the PAHs translocation by maize was reduced by Pb uptake, but not significantly affected by soil organic matters, pH or the other four heavy metals (Cr, Cu, Ni and Zn). This study for the first time provides the restricted factors of PAHs and heavy metal acropetal translocation by maize when they co-exist at wastewater irrigation sites.

Uptake, translocation, and metabolism of hydroxylated and methoxylated polychlorinated biphenyls in maize, wheat, and rice.

Hydroxylated polychlorinated biphenyls (OH-PCBs) have been found in the environment with high toxicity. Recently, methoxylated polychlorinated biphenyls (MeO-PCBs) were identified as new pollutants and detected in sewage sludge. This study presents a detailed investigation on the uptake, translocation, and metabolism of OH-PCBs and MeO-PCBs in typical crops including maize, wheat, and rice. The interconversion between OH-PCBs and MeO-PCBs were observed. Demethylation of MeO-PCBs was favored over methylation of OH-PCBs. The metabolites were mainly generated in the roots and then translocated to the shoots. Analog-specific differences showed that the accumulation amounts of MeO-PCBs were higher than those of OH-PCBs in the crops. The translocation abilities followed this order: 3'-OH-CB-65 > 4'-OH-CB-101 > 3'-MeO-CB-65 > 4'-MeO-CB-101. The conversion rates were generally higher for 4'-OH-CB-101 than 3'-OH-CB-65 and higher for 4'-MeO-CB-101 than 3'-MeO-CB-65. Interspecies variability among the crops was also observed. The amounts of metabolites and acropetal translocation inside the plants were the greatest for maize. However, the concentration of compounds normalized by the mass of corresponding plant tissue was highest in wheat. These findings provide valuable information for a better understanding of the phytoaccumulation and phytotransformation of OH-PCBs and MeO-PCBs.

Silicon-enhanced oxalate exudation contributes to alleviation of cadmium toxicity in wheat

Cadmium (Cd) contamination is a threat to agricultural plant production. Silicon (Si) supply to Cd-stressed plants is known to ameliorate growth by decreasing the concentrations of Cd in plant tissues. To elucidate the underlying mechanism in wheat, hydroponic experiments were conducted under Cd stressed conditions in the presence or absence of Si, with special emphasis on root morphology, root exudation of oxalate and Cd allocation. We found that Si supply decreased Cd accumulation in plant, which resulted in better plant growth. Further studies of subcellular distribution showed that Si did not accelerate Cd accumulation into cell walls or vacuoles. Since acropetal translocation of Cd was not affected regardless of Si addition as well, we reason the Si-related decrease in leaf Cd concentrations was based on exclusion at the root side. This effect can be traced back to oxalate exudation by roots. In this study, the ability to exude oxalate through the root apex in Cd-stressed plants was weakened, while Si addition recovered the ability, thus reducing Cd uptake by roots. To our knowledge, we showed the first time that Si decreases Cd uptake by the increase of root oxalate exudation as an avoidance mechanism. Meanwhile, we also found Si supply increased total number of root tips which might facilitate root oxalate exudation.

Neonicotinoid insecticide systemicity in soybean plants and its effect on brown stink bugs

ABSTRACT During the application of pesticides on soybean fields, a vertical deposition gradient of the product can occur throughout the canopy, resulting in difficulties for controlling stink bugs that are in the middle and lower thirds of plants. This study aimed at evaluating the systemicity of thiamethoxam insecticide in different soybean phenological stages, using brown stink bugs as bioindicators of the pesticide efficacy. The study combined product application sites (lower, middle and upper third) and stink bugs infestation areas at five soybean phenological stages (R2, R3, R4, R5.2 and R6). For the R2 and R5.2 stages, plants presented acropetal translocation of the product, being the effect more evident in the R2 stage. For the R3, R4 and R6 stages, the product translocation was not sufficient for controlling the stink bugs. In all stages, for treatments with direct exposure (same infestation and spraying place), stink bugs were satisfactorily controlled.

Uptake Pathway, Translocation, and Isomerization of Hexabromocyclododecane Diastereoisomers by Wheat in Closed Chambers

To study the uptake pathways of 3 main hexabromocyclododecane diastereoisomers (α-, β-, and γ-HBCDs) in wheat, four closed chambers were designed to expose wheat to HBCDs via air and/or soil for 4 weeks. The results showed that HBCDs could be absorbed by wheat both via root from soil and via leaf from air. The Rt values (ratio of HBCDs from root-to-leaf translocation to the total accumulation in leaves) ranging from 14.4 to 29.8% suggested that acropetal translocation within wheat was limited. A negative linear relationship was found between log Rt and log Kow of the HBCD diastereoisomers (p < 0.05). The bioconcentration factors (BCFs, (μg/g wheat tissues)/(μg/g soil)) were in the order α- > β- > γ-HBCD in wheat roots and stems, being negatively related to their Kow values. No such correlation was found in leaves, where the HBCDs came mainly from air distribution. The results of enantiomeric fractions indicated that the (-)-enantiomer of α- and γ-HBCDs and the (+)-β-enantiomer were selectively accumulated. Furthermore, β- and γ-HBCDs were transformed to α-HBCD in the wheat, with 0.309-4.80% and 0.920-8.40% bioisomerization efficiencies at the end of the experiment, respectively, being the highest in leaves. Additionally, no isomerization product from α-HBCD was found.

Could Uptake and Acropetal Translocation of PBDEs by Corn Be Enhanced Following Cu Exposure? Evidence from a Root Damage Experiment.

Cocontamination by heavy metals and persistent organic pollutants (POPs) is ubiquitous in the environment. Fate of POPs within soil/water-plant system is a significant concern and an area where much uncertainty still exists when plants suffered cotoxicity from POPs and metals. This study investigated the fate of polybrominated diphenyl ethers (PBDEs) when copper (Cu) was present within the soil/water-plant system using pot and hydroponic experiments. The presence of Cu was found to induce damage to the root cell membranes of corn (Zea mays L. cv. Nongda 108) with increasing concentration in both shoots and roots. The PBDE congeners BDE209 and BDE47 in shoots were also enhanced with the increasing electrolytic leakage from root, attributed to Cu damage, and the highest shoot BDE209 and BDE47 levels were observed under the highest Cu dosage. In addition, positive correlations were observed between the PBDE content of corn shoots and the electrolytic leakage of corn roots. These results indicated that within a defective root system, more PBDEs will penetrate the roots and are acropetally translocated in the shoots. The potential ecological risk associated with the translocation and accumulation of POPs into plant shoots needs careful reconsideration in media cocontaminated with metals and POPs, whereas often ignored or underestimated in environmental risk assessments.

Uptake, translocation and biotransformation kinetics of BDE-47, 6-OH-BDE-47 and 6-MeO-BDE-47 in maize (Zea mays L.)

This study presents a detailed kinetic investigation on the uptake, acropetal translocation and transformation of BDE-47, 6-OH-BDE-47 and 6-MeO-BDE-47 in maize (Zea mays L.) by hydroponic exposure. Root uptake followed the order: BDE-47 > 6-MeO-BDE-47 > 6-OH-BDE-47, while 6-OH-BDE-47 was the most prone to acropetal translocation. Debromination rates of BDE-47 were 1.31 and 1.46 times greater than the hydroxylation and methoxylation rates, respectively. Transformation from BDE-47 to lower brominated OH/MeO-PBDEs occurred mainly through debromination first followed by hydroxylation or methoxylation. There was no transformation from 6-OH-BDE-47 or 6-MeO-BDE-47 to PBDEs. Methylation rate of 6-OH-BDE-47 was twice as high as that of 6-MeO-BDE-47 hydroxylation, indicating methylation of 6-OH-BDE-47 was easier and more rapid than hydroxylation of 6-MeO-BDE-47. Debromination and isomerization were potential metabolic pathways for 6-OH-BDE-47 and 6-MeO-BDE-47 in maize. This study provides important information for better understanding the mechanism on plant uptake and transformation of PBDEs.

Physiological Basis for Triazine Herbicide Tolerance in Bermudagrass, Seashore Paspalum, and Zoysiagrass

ABSTRACTAtrazine and simazine control weeds in warm‐season turfgrasses, but excessive injury limits applications to sensitive species. The objective of this research was to evaluate the physiological basis for differential tolerances of bermudagrass (Cynodon dactylon (L.) Pers.), seashore paspalum (Paspalum vaginatum Sw.), and zoysiagrass (Zoysia japonica Steud.) to atrazine and simazine. In greenhouse experiments, hierarchical shoot mass reductions from the nontreated by species were: seashore paspalum &gt; bermudagrass &gt; zoysiagrass for atrazine and seashore paspalum &gt; bermudagrass = zoysiagrass for simazine. Atrazine and simazine treatments to soil only or foliar plus soil reduced shoot mass similarly, averaging 45% from nontreated, while foliar‐only treatments reduced shoot mass 22% from the nontreated. Species rank for root absorption of both herbicides after 48 h from high to low was seashore paspalum &gt; bermudagrass &gt; zoysiagrass. All species had acropetal translocation of 14C‐atrazine and 14C‐simazine, but bermudagrass and zoysiagrass translocated ∼10% more 14C than seashore paspalum after 48 h. Hierarchical species rank for nonmetabolized 14C‐atrazine translocation to shoots after 8 h from high to low was seashore paspalum &gt; bermudagrass &gt; zoysiagrass. All species metabolized 14C‐atrazine to hydroxyatrazine and two unidentified metabolites in root and shoots. All species metabolized simazine to hydroxysimazine and two other metabolites in shoots. Seashore paspalum had less total metabolism of 14C‐simazine than bermudagrass and zoysiagrass and produced fewer metabolites in roots. Results suggest bermudagrass and seashore paspalum susceptibility to atrazine is associated with greater absorption and translocation of the parent herbicide to shoots than zoysiagrass. Seashore paspalum susceptibility to injury from simazine is associated with differences in absorption and metabolism from tolerant turfgrasses bermudagrass and zoysiagrass.

Dithiopyr Controls Common Lespedeza (Kummerowia striata) in Bermudagrass

Common lespedeza is a problematic summer annual weed in bermudagrass lawns, with limited PRE herbicides available for control. Dithiopyr is a pyridine herbicide primarily used for PRE grassy weed control but has shown potential efficacy for controlling annual legumes. The objectives of this research were to evaluate efficacy and behavior of dithiopyr in common lespedeza. In a 3-yr field experiment, sequential dithiopyr applications at 0.42 or 0.56 kg ai ha−1beginning in late winter and single applications of dithiopyr at 0.56 kg ai ha−1in spring controlled common lespedeza ≥ 88%. Single and sequential applications of indaziflam at 0.035 and 0.053 kg ai ha−1provided poor control (&lt; 70%) of common lespedeza by late summer. In laboratory experiments, bermudagrass and common lespedeza had similar foliar absorption of14C-dithiopyr, averaging 10% of the14C applied, and both species retained &gt; 80% of14C in the treated leaf at 72 h after treatment (HAT). Common lespedeza translocated 6 times more root-absorbed14C to shoots than bermudagrass and had 2.8 times greater absorption (Bq mg−1) at 72 HAT. In metabolism experiments, parent herbicide levels measured ≥ 84% of extracted14C in both species at 1, 3, and 7 d after treatment. Overall, dithiopyr effectively controls common lespedeza in bermudagrass as a PRE treatment in spring. Susceptibility of common lespedeza to dithiopyr is associated with acropetal translocation and greater herbicide concentrations compared with a tolerant species, bermudagrass.