Arabidopsis response to copper is mediated by density and root exudates: Evidence that plant density and toxic soils can shape plant communities.

PREMISE: Plants grown at high densities show increased tolerance to heavy metals for reasons that are not clear. A potential explanation is the release of citrate by plant roots, which binds metals and prevents uptake. Thus, pooled exudates at high plant densities might increase tolerance. We tested this exclusion facilitation hypothesis using mutants of Arabidopsis thaliana defective in citrate exudation. METHODS: Wild type Arabidopsis and two allelic mutants for the Ferric Reductase Defective 3 (FRD3) gene were grown at four densities and watered with copper sulfate at four concentrations. Plants were harvested before bolting and dried. Shoot biomass was measured, and shoot material and soil were digested in nitric acid. Copper contents were determined by atomic absorption. RESULTS: In the highest-copper treatment, density-dependent reduction in toxicity was observed in the wild type but not in FRD3 mutants. For both mutants, copper concentrations per gram biomass were up to seven times higher than for wild type plants, depending on density and copper treatment. In all genotypes, total copper accumulation was greater at higher plant densities. Plant size variation increased with density and copper treatment because of heterogeneous distribution of copper throughout the soil. CONCLUSIONS: These results support the hypothesis that citrate exudation is responsible for density-dependent reductions in toxicity of metals. Density-dependent copper uptake and growth in contaminated soils underscores the importance of density in ecotoxicological testing. In soils with a heterogeneous distribution of contaminants, competition for nontoxic soil regions may drive size hierarchies and determine competitive outcomes.

Metal exposures from source materials for artisanal aluminum cookware.

Artisanal aluminum cookware releases lead and other metals that pose significant health risk for people in low and middle-income countries. Cookware is made from recycled engine and electronic appliance parts, cans, and other materials. We obtained fourteen custom-made pots from Ghana, produced from seven different scrap aluminum sources. We sought to determine whether avoiding certain source materials could reduce leaching of metals. Cooking was simulated using dilute acetic acid and palm oil. Aluminum released from all pots exceeded recommended guidelines. Variable amounts of lead, cadmium, chromium, nickel and other metals were leached, with the most lead coming from auto radiators and mixed metals. Pots made from engine blocks did not yield detectable amounts of lead. All pots released potentially harmful concentrations of two or more metals. Selective scrap aluminum sourcing for recycled cookware does not avoid metal contamination of food, although some sources may release lower concentrations of certain metals.

Buyer beware: Inexpensive, high cadmium jewelry can pose severe health risks.

The use of cadmium to produce inexpensive jewelry has recently been documented. Governments have adopted varying standards, with US states focused on either total cadmium content or extractable cadmium from children's jewelry, while the European Union has adopted a limit of 100 mg/kg cadmium for all jewelry. This study evaluated 80 items purchased at a discount jewelry store. The objective was to determine prevalence of cadmium in this jewelry, the amount of cadmium released by simulated mouthing or ingestion, and to confirm previous reports that damage to jewelry can increase cadmium release. Finally, a modified toxicity characteristic leaching procedure (TCLP) assessed the potential for jewelry to release cadmium after disposal. Thirty-two (40%) items showed detectable cadmium by X-ray fluorescence. Nine high­cadmium pendants and rings with cadmium content ranging from 31.3 to 89.2% were subjected to extractions simulating mouthing or ingestion. Seven of nine items extracted in dilute saline to simulate mouthing released more than the US recommended maximum of 18 micrograms. Damaged jewelry released more cadmium for most items tested, with one ring yielding an average of 10,600 micrograms. Two pendants small enough to be swallowed were tested using dilute HCl to simulate ingestion. While one pendant did not release cadmium in excess of the US recommended maximum of 200 micrograms even when damaged, the other released an average of 63,100 micrograms after being damaged. Fourteen of fifteen samples of two high cadmium charms extracted using a modified TCLP extraction exceeded the 1.0 mg/L TCLP limit for cadmium, averaging 13.1 and 9.6 mg/L respectively for the two charms. These results demonstrate that high­cadmium jewelry may pose a serious hazard if mouthed or ingested, and that regulatory standards that do not take into account the potential for increased release of cadmium resulting from damage to jewelry electroplating are inadequate.

Plant Density and Rhizosphere Chemistry: Does Marigold Root Exudate Composition Respond to Intra- and Interspecific Competition?

The development of techniques to non-destructively monitor allelochemical dynamics in soil using polydimethylsiloxane (PDMS) microtubing (silicone tubing microextraction, or STME) provides a means to test important ecological hypotheses regarding the roles of these compounds in plant-plant interactions. The objective of this study was to investigate the impact of intra- and interspecific competition on the exudation of thiophenes by marigolds (Tagetes patula L.). Marigolds were grown at a density of 1, 3 and 5 plants in pots (8.75 × 8.75 cm) containing two STME samplers. An additional treatment included one marigold surrounded by four velvetleaf (Abutilon theophrasti L.) plants. Marigold roots released two primary thiophenes, 3-buten-1-ynyl)-2,2'-bithienyl and α-terthienyl, which are readily absorbed by silicone microtubing. Thiophene exudation was monitored over the period 15-36 days after planting, at 2-5 day intervals. At the end of the study, root and soil samples were also analyzed for thiophene content. Thiophene production per plant increased over time, and thiophene release was strongly correlated with plant size. These results indicate that thiophene release in this study was passively controlled by resource availability. However, poor growth of velvetleaf plants competing with marigold suggests that thiophenes negatively influenced velvetleaf growth. This study, then, provides indirect evidence that thiophene exudation is insensitive to neighbor identity but differentially effective in inhibiting the growth of heterospecific neighbors.

Metal exposures from aluminum cookware: An unrecognized public health risk in developing countries.

Removing lead from gasoline has resulted in decreases in blood lead levels in most of the world, but blood lead levels remain elevated in low and middle-income countries compared to more developed countries. Several reasons for this difference have been investigated, but few studies have examined the potential contribution from locally-made aluminum cookware. In a previous study of cookware from a single African country, Cameroon, artisanal aluminum cookware that is made from scrap metal released significant quantities of lead. In this study, 42 intact aluminum cookware items from ten developing countries were tested for their potential to release lead and other metals during cooking. Fifteen items released ≥1 microgram of lead per serving (250mL) when tested by boiling with dilute acetic acid for 2h. One pot, from Viet Nam, released 33, 1126 and 1426 micrograms per serving in successive tests. Ten samples released >1 microgram of cadmium per serving, and fifteen items released >1 microgram of arsenic per serving. The mean exposure estimate for aluminum was 125mg per serving, more than six times the World Health Organization's Provisional Tolerable Weekly Intake of 20mg/day for a 70kg adult, and 40 of 42 items tested exceeded this level. We conducted preliminary assessments of three potential methods to reduce metal leaching from this cookware. Coating the cookware reduced aluminum exposure per serving by >98%, and similar reductions were seen for other metals as well. Potential exposure to metals by corrosion during cooking may pose a significant and largely unrecognized public health risk which deserves urgent attention.

Identification and localization of bioactive naphthoquinones in the roots and rhizosphere of Paterson's curse (Echium plantagineum), a noxious invader.

Bioactive plant secondary products are frequently the drivers of complex rhizosphere interactions, including those with other plants, herbivores and microbiota. These chemically diverse molecules typically accumulate in a highly regulated manner in specialized plant tissues and organelles. We studied the production and localization of bioactive naphthoquinones (NQs) in the roots of Echium plantagineum, an invasive endemic weed in Australia. Roots of E. plantagineum produced red-coloured NQs in the periderm of primary and secondary roots, while seedling root hairs exuded NQs in copious quantities. Confocal imaging and microspectrofluorimetry confirmed that bioactive NQs were deposited in the outer layer of periderm cells in mature roots, resulting in red colouration. Intracellular examination revealed that periderm cells contained numerous small red vesicles for storage and intracellular transport of shikonins, followed by subsequent extracellular deposition. Periderm and root hair extracts of field- and phytotron-grown plants were analysed by UHPLC/Q-ToF MS (ultra high pressure liquid chromatography coupled to quadrupole time of flight mass spectrometry) and contained more than nine individual NQs, with dimethylacrylshikonin, and phytotoxic shikonin, deoxyshikonin and acetylshikonin predominating. In seedlings, shikonins were first found 48h following germination in the root-hypocotyl junction, as well as in root hair exudates. In contrast, the root cortices of both seedling and mature root tissues were devoid of NQs. SPRE (solid phase root zone extraction) microprobes strategically placed in soil surrounding living E. plantagineum plants successfully extracted significant levels of bioactive shikonins from living roots, rhizosphere and bulk soil surrounding roots. These findings suggest important roles for accumulation of shikonins in the root periderm and subsequent rhizodeposition in plant defence, interference, and invasion success.

Lead exposure from aluminum cookware in Cameroon.

Blood lead levels have decreased following the removal of lead from gasoline in most of the world. However, numerous recent studies provide evidence that elevated blood lead levels persist in many low and middle-income countries around the world at much higher prevalence than in the more developed countries. One potential source of lead exposure that has not been widely investigated is the leaching of lead from artisanal aluminum cookware, which is commonly used in the developing world. Twenty-nine samples of aluminum cookware and utensils manufactured by local artisans in Cameroon were collected and analyzed for their potential to release lead during cooking. Source materials for this cookware included scrap metal such as engine parts, radiators, cans, and construction materials. The lead content of this cookware is relatively low (<1000 ppm by X-ray fluorescence), however significant amounts of lead, as well as aluminum and cadmium were released from many of the samples using dilute acetic acid extractions at boiling and ambient temperatures. Potential exposures to lead per serving were estimated to be as high as 260 µg, indicating that such cookware can pose a serious health hazard. We conclude that lead, aluminum and cadmium can migrate from this aluminum cookware during cooking and enter food at levels exceeding recommended public health guidelines. Our results support the need to regulate lead content of materials used to manufacture these pots. Artisanal aluminum cookware may be a major contributor to lead poisoning throughout the developing world. Testing of aluminum cookware in other developing countries is warranted.

Spatial and temporal dynamics of root exudation: how important is heterogeneity in allelopathic interactions?

Understanding allelopathy has been hindered by the lack of methods available to monitor the dynamics of allelochemicals in the soil. Previous work has demonstrated the feasibility of using polydimethylsiloxane (PDMS) microtubing (silicone tubing microextraction, or STME) to construct sampling devices to monitor the release of lipophilic allelochemicals from plant roots. The objective of this study was to use such sampling devices to intensively monitor thiophene fluxes beneath marigolds over several weeks to gain insight into the magnitude of temporal and spatial heterogeneity in these fluxes. Marigolds were grown in rhizoboxes (20.5 x 20.5 x 3.0 cm) with 16 individual STME samplers per box. Thiophene sampling and HPLC analysis began 45 days after planting. At the end of the study, roots around each sampler were analyzed by HPLC. Results confirmed the tremendous spatial and temporal heterogeneity in thiophene production seen in our previous studies. STME probes show that thiophene concentrations generally increase over time; however, these effects were sampling-port specific. When sampling ports were monitored at 12 h intervals, fluxes at each port ranged from 0 to 2,510 ng day(-1). Fluxes measured over daylight hr averaged 29 % higher than those measured overnight. Fluxes were less than 1 % on average of the total thiophene content of surrounding roots. While the importance of such heterogeneity, or "patchiness", in the root zone has been recognized for soil nutrients, the potential importance in allelopathic interactions has seldom been considered. The reasons for this variability are unclear, but are being investigated. Our results demonstrate that STME can be used as a tool to provide a more finely-resolved picture of allelochemical dynamics in the root zone than has previously been available.

Plant growth responses to inorganic environmental contaminants are density-dependent: experiments with copper sulfate, barley and lettuce.

The density-dependence of terrestrial plant-plant interactions in the presence of toxins has previously been explored using biodegradable compounds. We exposed barley and lettuce to four copper concentrations at four stand densities. We hypothesized that toxin effects would decrease and Cu uptake would increase at increasing plant densities. We analyzed toxin effects by (a) comparing plant biomasses and (b) using a recent regression model that has a separate parameter for the interaction of resource competition and toxin interference. Plant response to Cu was density-dependent in both experiments. Total Cu uptake by barley increased and the dose per plant decreased as plant density increased. This study is the first to demonstrate that plant density mediates plant response to metals in soil in a predictable way. This highlights the need to explore the mechanisms for and consequences of these effects, and to integrate the use of several plant densities into standard ecotoxicological testing.

Evidence does not support a role for gallic acid in Phragmites australis invasion success.

Gallic acid has been reported to be responsible for the invasive success of nonnative genotypes of Phragmites australis in North America. We have been unable to confirm previous reports of persistent high concentrations of gallic acid in the rhizosphere of invasive P. australis, and of high concentrations of gallic acid and gallotannins in P. australis rhizomes. The half-life of gallic acid in nonsterile P. australis soil was measured by aqueous extraction of soils and found to be less than 1 day at added concentrations up to 10,000 µg g(-1). Furthermore, extraction of P. australis soil collected in North Carolina showed no evidence of gallic acid, and extractions of both rhizomes and leaves of samples of four P. australis populations confirmed to be of invasive genotype show only trace amounts of gallic acid and/or gallotannins. The detection limits were less than 20 µg gallic acid g(-1) FW in the rhizome samples tested, which is approximately 0.015 % of the minimum amount of gallic acid expected based on previous reports. While the occurrence of high concentrations of gallic acid and gallotannins in some local populations of P. australis cannot be ruled out, our results indicate that exudation of gallic acid by P. australis cannot be a primary, general explanation for the invasive success of this species in North America.

Fungal superhighways: do common mycorrhizal networks enhance below ground communication?

In many natural communities communication between plants and other organisms below ground drives community dynamics. This communication is primarily through the release and detection of infochemicals, which must traverse the soil matrix to be effective. In this opinion article, we propose the Network Enhanced Bioactive Zone (NEBaZ) model, which posits that common mycorrhizal networks (CMNs) increase the bioactive zones of infochemicals by serving as superhighways directly connecting plants below ground. Here we argue that infochemical transport via CMNs allows for systemic defense signaling across plant populations and directed allelochemical delivery to target plants. Plant-animal interactions may also be facilitated by CMNs, suggesting that these fungal networks may be crucial components of many natural ecosystems.

The fungal fast lane: common mycorrhizal networks extend bioactive zones of allelochemicals in soils.

Allelopathy, a phenomenon where compounds produced by one plant limit the growth of surrounding plants, is a controversially discussed factor in plant-plant interactions with great significance for plant community structure. Common mycorrhizal networks (CMNs) form belowground networks that interconnect multiple plant species; yet these networks are typically ignored in studies of allelopathy. We tested the hypothesis that CMNs facilitate transport of allelochemicals from supplier to target plants, thereby affecting allelopathic interactions. We analyzed accumulation of a model allelopathic substance, the herbicide imazamox, and two allelopathic thiophenes released from Tagetes tenuifolia roots, by diffusion through soil and CMNs. We also conducted bioassays to determine how the accumulated substances affected plant growth. All compounds accumulated to greater levels in target soils with CMNs as opposed to soils without CMNs. This increased accumulation was associated with reduced growth of target plants in soils with CMNs. Our results show that CMNs support transfer of allelochemicals from supplier to target plants and thus lead to allelochemical accumulation at levels that could not be reached by diffusion through soil alone. We conclude that CMNs expand the bioactive zones of allelochemicals in natural environments, with significant implications for interspecies chemical interactions in plant communities.

Bioavailability of cadmium in inexpensive jewelry.

OBJECTIVES: We evaluated the bioavailability of Cd in 86 components of 57 jewelry items found to contain high levels of Cd (> 10,000 ppm) by X-ray fluorescence (XRF), using extractions that simulate mouthing or swallowing of jewelry items. METHODS: We screened jewelry for Cd content by XRF. Bioavailability was measured in two ways. Items were placed in saline solution at 37°C for 6 hr to simulate exposures from mouthing of jewelry items. Items were placed in dilute hydrochloric acid (HCl) at 37°C for 6-96 hr, simulating the worst-case scenario of a child swallowing a jewelry item. Damaged pieces of selected samples were also extracted by both methods to determine the effect of breaching the outer plating on bioavailability. Total Cd content of all items was determined by atomic absorption. RESULTS: The 6-hr saline extraction yielded as much as 2,200 µg Cd, and 24-hr dilute HCl extraction yielded a maximum of > 20,000 µg Cd. Leaching of Cd in dilute HCl increased linearly over 6-96 hr, indicating potential for increasing harm the longer an item remains in the stomach. Damage to jewelry by breaching the outer plating generally, but not always, increased Cd release. Bioavailability did not correlate directly with Cd content. CONCLUSIONS: These results indicate the potential for dangerous Cd exposures to children who wear, mouth, or accidentally swallow high-Cd jewelry items.

Constituents of Calamintha ashei: effects on Florida sandhill species.

Chemical constituents of the perennial shrub Calamintha ashei have been characterized as part of our investigation of the allelopathic properties of this plant. Besides the known monoterpenes, (+)-evodone, (-)-calaminthone and (+)-desacetylcalaminthone, fresh aerial parts of C. ashei provided six new menthofurans, two new germacrane sesquiterpenes, and the six, known flavonoids: 5-desmethoxynobiletin, 5-hydroxy-6,7,8,4'-tetramethoxyflavone, 5,4'-dihydroxy-6,7,8,3'-tetramethoxyflavone, thymonin, 5,4'-dihydroxy-6,7-dimethoxyflavone and 6-hydroxy-7,3'-dimethoxyluteolin. The structures of the new compounds were elucidated by spectroscopic methods and comparison of their 1H NMR spectra with those of structurally related compounds. The molecular structures of (+)-evodone, 5-desmethoxynobiletin (5-hydroxy-6,7,8,3',4'-pentamethoxyflavone) and the triacetate of thymonin (7,8,3'-trimethoxy-5,6,4'-triacetoxyflavone), were determined by single crystal X-ray diffraction. Saturated aqueous solutions of menthofuran, (+)-evodone, (-)-calaminthone, (+)-desacetylcalaminthone, 4alpha,5beta-diacetoxymenthofuran, as well as mixtures of (+)-evodone and (+)-desacetylcalaminthone inhibited the germination and root growth of Schizachyrium scoparium and Leptochloa dubia, two native Florida sandhill grasses, as well as Lactuca sativa. (+)-Evodone and (+)-desacetylcalaminthone were the most active. 5-Hydroxy-6,7,8,3',4'-pentamethoxyflavone and 5,4'-dihydroxy-6,7,8,3'-tetramethoxyflavone and mixtures of the two flavonoids in aqueous as well as in saturated aqueous solutions ofursolic acid were tested on the same species, but showed no significant activity.

Assessment of leaching potential of highly leaded jewelry.

Lead is a potent neurotoxin particularly toxic to young children, and in response to recent poisonings of children and high levels of lead contamination in children's jewelry, US regulatory standards for lead content in these items have become much more stringent. Parents are often advised to throw out suspect items in the trash. While household wastes are generally exempt from consideration as hazardous waste, the potential for leaching of hazardous quantities of lead from such items is unknown. A modified Toxicity Characteristic Leaching Procedure (TCLP), in which intact jewelry components were subjected to leaching, was used to evaluate the potential for leaching of lead from highly leaded jewelry. Of 62 jewelry components tested, 61 exceeded the US regulatory standard for lead of 5mg/L, and leachate lead concentrations averaged 1460 mg/L. Twenty-six of the component items tested yielded TCLP lead concentrations exceeding 1000 mg/L. These results demonstrate that highly leaded jewelry items may leach significant amounts of lead, and provide another reason to remove lead from these products. Furthermore, these results suggest that while the volume of such items in the municipal solid waste (MSW) stream is small, they have the potential to contribute significant quantities of lead to MSW leachates.

Direct and indirect effects of invasive plants on soil chemistry and ecosystem function.

Invasive plants have a multitude of impacts on plant communities through their direct and indirect effects on soil chemistry and ecosystem function. For example, plants modify the soil environment through root exudates that affect soil structure, and mobilize and/or chelate nutrients. The long-term impact of litter and root exudates can modify soil nutrient pools, and there is evidence that invasive plant species may alter nutrient cycles differently from native species. The effects of plants on ecosystem biogeochemistry may be caused by differences in leaf tissue nutrient stoichiometry or secondary metabolites, although evidence for the importance of allelochemicals in driving these processes is lacking. Some invasive species may gain a competitive advantage through the release of compounds or combinations of compounds that are unique to the invaded community­the "novel weapons hypothesis." Invasive plants also can exert profound impact on plant communities indirectly through the herbicides used to control them. Glyphosate, the most widely used herbicide in the world, often is used to help control invasive weeds, and generally is considered to have minimal environmental impacts. Most studies show little to no effect of glyphosate and other herbicides on soil microbial communities. However, herbicide applications can reduce or promote rhizobium nodulation and mycorrhiza formation. Herbicide drift can affect the growth of non-target plants, and glyphosate and other herbicides can impact significantly the secondary chemistry of plants at sublethal doses. In summary, the literature indicates that invasive species can alter the biogeochemistry of ecosystems, that secondary metabolites released by invasive species may play important roles in soil chemistry as well as plant-plant and plant-microbe interactions, and that the herbicides used to control invasive species can impact plant chemistry and ecosystems in ways that have yet to be fully explored.

Assessment of the phytotoxic potential of m-tyrosine in laboratory soil bioassays.

The significance of soil-allelochemical interactions was addressed in this paper through studies conducted with m-tyrosine, an amino acid analogue and a potent plant growth inhibitor, in a series of laboratory assays performed in field soil or growth media. The studies were performed as a basis for further evaluation of m-tyrosine activity in field soils containing living plant roots. Here, we examined the role of common soil amendments, including ammonium nitrate fertilizer and activated carbon, in overcoming plant growth inhibition in soils in a laboratory setting by using lettuce as a sensitive indicator of plant toxicity. The phytotoxicity of m-tyrosine was not influenced significantly by soil N amendment; however, when significant amounts of activated carbon were added to the soil medium, growth inhibition in treated lettuce seedlings was strongly reduced. Soil texture did not influence the bioavailability or activity of m-tyrosine, as activity in high organic growth media was similar to that of sand and soil mixtures. Similar to other purported allelochemicals, soil persistence of m-tyrosine was limited, with a predicted half life of less than 1 day in soil in a controlled laboratory setting. Rapid degradation of this molecule likely was due to microbial activity but degradation did not appear to be influenced significantly by soil N amendment. Given the observed activity of m-tyrosine in soil and growth media on seedling growth, potential may exist for development of m-tyrosine as a soil applied herbicide if formulations can be stabilized under soil conditions.

In situ silicone tube microextraction: a new method for undisturbed sampling of root-exuded thiophenes from marigold (Tagetes erecta L.) in soil.

The difficulties of monitoring allelochemical concentrations in soil and their dynamics over time have been a major barrier to testing hypotheses of allelopathic effects. Here, we evaluate three diffusive sampling strategies that employ polydimethylsiloxane (PDMS) sorbents to map the spatial distribution and temporal dynamics of root-exuded thiophenes from the African marigold, Tagetes erecta. Solid phase root zone extraction (SPRE) probes constructed by inserting stainless steel wire into PDMS tubing were used to monitor thiophene concentrations at various depths beneath marigolds growing in PVC pipes. PDMS sheets were used to map the distribution of thiophenes beneath marigolds grown in thin glass boxes. Concentrations of the two major marigold thiophenes measured by these two methods were extremely variable in both space and time. Dissection and analysis of roots indicated that distribution of thiophenes in marigold roots also was quite variable. A third approach used 1 m lengths of PDMS microtubing placed in marigold soil for repeated sampling of soil without disturbance of the roots. The two ends of the tubing remained out of the soil so that solvent could be washed through the tubing to collect samples for HPLC analysis. Unlike the other two methods, initial experiments with this approach show more uniformity of response, and suggest that soil concentrations of marigold thiophenes are affected greatly even by minimal disturbance of the soil. Silicone tube microextraction gave a linear response for alpha-terthienyl when maintained in soils spiked with 0-10 ppm of this thiophene. This method, which is experimentally simple and uses inexpensive materials, should be broadly applicable to the measurement of non-polar root exudates, and thus provides a means to test hypotheses about the role of root exudates in plant-plant and other interactions.

Dynamic root exudation of sorgoleone and its in planta mechanism of action.

The oily droplets exuded from the root hairs of sorghum are composed of a 1:1 ratio of sorgoleone and its lipid resorcinol analogue. The production of these droplets appears to be suppressed when c. 20 microg of exudate mg(-1) root dry weight accumulates at the tip of the root hairs. However, more exudate is produced following gentle washing of the roots with water, suggesting that the biosynthesis of lipid benzoquinones and resorcinols is a dynamic process. Sorgoleone interferes with several molecular target sites, including photosynthetic electron transport, in in vitro assays. However, the in planta mechanism of action of sorgoleone remains controversial because it is not clear whether this lipid benzoquinone exuding from the roots of sorghum is taken up by roots of the receiving plants and translocated to their foliage where it must enter the chloroplast and inhibit PSII in the thylakoid membrane. Experiments designed to test the in planta mode of action of sorgoleone demonstrated that it has no effect on the photosynthesis of older plants, but inhibits photosynthesis in germinating seedlings. Sorgoleone is not translocated acropetally in older plants, but can be absorbed through the hypocotyl and cotyledonary tissues. Therefore, the mode of action of sorgoleone may be the result of inhibition of photosynthesis in young seedlings in concert with inhibition of its other molecular target sites in older plants.

Lead contamination of inexpensive seasonal and holiday products.

Lead is a potent neurotoxin and because of this, the US regulatory limit for lead content of paint on items intended for children is 0.06% by weight. There were numerous recalls of name-brand toys in the United States for lead paint contamination during 2007. Most of these items were manufactured in China. Seasonal and holiday items are inexpensive and often directed specifically toward children, yet the use of lead paints in these products has not been widely recognized. The objective of this study was to determine the extent of lead contamination in this product category. Ninety-five samples were tested, including primarily Halloween and Easter products. Twelve of the products were found to contain lead in excess of the current US regulatory limit of 0.06% by weight for lead in paints on items intended for children. The high percentage of products found to be contaminated in this limited sampling implies that many more lead-painted items are being sold. These results suggest that the potential hazards of seasonal and holiday products deserve the attention of government agencies seeking to limit the exposure of children to lead.