Lettuce Root Elongation Research Articles

Chemical stabilization of medical waste fly ash using chelating agent and phosphates: Heavy metals and ecotoxicity evaluation.

Chemical stabilization of heavy metals in medical waste fly ash has been carried out using the following compounds: a chelating agent (Ashnite S803), a commercial acidic phosphoric acid solution (Ashnite R303) as well as basic one (Ashnite R201). In order to predict the leachability of heavy metals, Japanese Leaching Test (JLT-13) procedure was applied to the stabilized fly ash products. An ecotoxicity assessment of the stabilized fly ash products leachate and the unstabilized fly ash leachate was conducted using a battery of bioassays based on lettuce root elongation inhibition, Daphnia magna mortality and Vibrio fischeri photoinhibition. The results showed that the three stabilizing agents were able to significantly decrease (ANOVA, P < 0.05) the concentration of heavy metals in the leachates. Although the leachate from both stabilized and unstabilized fly ash were very toxic to lettuce and daphnids, the incorporation of these stabilizing agents diminished significantly (ANOVA, P < 0.05) the toxicity of the leachates towards the three tested organisms. Pearson correlation analysis was used to analyze the strength of the relationship between chemical elements concentration in the leachate and bioassays results. Most of the heavy metals in the leachate were significantly correlated (ANOVA, P < 0.05) with the toxicity values of the bioassays. However, the correlation was not found between the concentration of dissolved organic carbon (DOC) and the toxicity effect of the leachate to the tested organisms.

Effects of functionalized and nonfunctionalized single‐walled carbon nanotubes on root elongation of select crop species

Single-walled carbon nanotubes have many potential beneficial uses, with additional applications constantly being investigated. Their unique properties, however, create a potential concern regarding toxicity, not only in humans and animals but also in plants. To help develop protocols to determine the effects of nanotubes on plants, we conducted a pilot study on the effects of functionalized and nonfunctionalized single-walled carbon nanotubes on root elongation of six crop species (cabbage, carrot, cucumber, lettuce, onion, and tomato) routinely used in phytotoxicity testing. Nanotubes were functionalized with poly-3-aminobenzenesulfonic acid. Root growth was measured at 0, 24, and 48 h following exposure. Scanning-electron microscopy was used to evaluate potential uptake of carbon nanotubes and to observe the interaction of nanotubes with the root surface. In general, nonfunctionalized carbon nanotubes affected root length more than functionalized nanotubes. Nonfunctionalized nanotubes inhibited root elongation in tomato and enhanced root elongation in onion and cucumber. Functionalized nanotubes inhibited root elongation in lettuce. Cabbage and carrots were not affected by either form of nanotubes. Effects observed following exposure to carbon nanotubes tended to be more pronounced at 24 h than at 48 h. Microscopy images showed the presence of nanotube sheets on the root surfaces, but no visible uptake of nanotubes was observed.

Bioaugmentation and biostimulation effects on PAH dissipation and soil ecotoxicity under controlled conditions

The degradation of spiked anthracene (ANT), pyrene (PYR) and benzo[ a]pyrene (B[ a]P) in soil (3000 mg ∑ 3 PAHs kg −1 dry soil) was studied in aerobically incubated microcosms for 120 d. The applied treatments aimed at enhancing PAH removal from the heavily contaminated soils are: (i) bioaugmentation by adding aged PAH-contaminated soil (ACS) containing activated indigenous degraders; and (ii) combined bioaugmentation/biostimulation by incorporating sewage sludge compost (SSC) and decaying rice straw (DRS). The adopted treatments produced higher PAH dissipation rates than those observed in unamended PAH-spiked soils, especially for ANT and PYR in the presence of DRS or ACS (>96%). However, B[ a]P was the most recalcitrant hydrocarbon to biodegradation. Extracellular enzyme investigation revealed the existence of ligninolytic activities in all soil treatments, including control but no relationship could be found with PAH dissipation. The ecotoxicological assessment indicated that regardless of applied treatment, PAH-spiked soils were chronically lethal to ostracod Heterocypris incongruens and confirmed the sensitivity of the microcrustacean to the concomitant presence of these three hydrocarbons. Lettuce root elongation inhibition was correlated with PAH level but the presence of SSC conferred a strong phytotoxic capacity to PAH-spiked soils. DRS amendment may constitute a cost-effective alternative for hydrocarbon bioremediation as it has impacted positively on soil microbial activity and enhanced PAH removal with no apparent changes in soil physico-chemical properties.

Effects of anthracene, pyrene and benzo[ a]pyrene spiking and sewage sludge compost amendment on soil ecotoxicity during a bioremediation process

The fate of spiked anthracene, pyrene and benzo[ a]pyrene in soil with or without sewage sludge compost was assessed during a 6-month bioremediation process simulating landfarming. Bioassays and physico-chemical analyses were employed to monitor toxicity change in soil samples and elutriates through ten sampling campaigns. Pearson product–moment correlation coefficient was determined to measure the strength of relationship between bioassays and physico-chemical analyses. The PAH dissipation in soil was enhanced after the first water addition, and the remaining amounts at the end of the experiment were positively correlated to the number of benzene rings and the presence of sewage sludge compost. Toxicity of soil elutriates to Daphnia magna was evident at early stages, originating exclusively from sewage sludge compost amendment. The lettuce root elongation was continuously inhibited by elutriates for all the treatments including control soil, probably due to high salinity or to unaddressed leachable phytotoxic compounds that were present in the experimental soil. The newly developed direct solid-phase chronic toxicity test using ostracod ( Heterocypris incongruens) succeeded in evaluating the soil-bound PAH toxicity, as PAHs could not be detected in elutriates.

Phytotoxicity and Detoxification of Fresh Coir Dust and Coconut Shell

Phytotoxicity and detoxification of fresh coir dust and milled coconut shell were studied using lettuce bioassay, phytotoxin analysis and incubation with liming and other amendments at different temperatures. Fresh coir dust and fresh fine coconut shell severely inhibited root elongation of lettuce. The phytotoxicity was attributed to the phenolic compounds in the substrates and the higher concentration of water-soluble phenolic compounds in the finer substrates aggravated the phytotoxicity. The critical concentration of phenolic compounds toxic to lettuce root growth was found to be about 2 mg L−1. Fresh coir dust and coconut shell could be detoxified by incubation. Liming and elevated incubation temperature significantly increased the processes of detoxification.

Synergism of polygodial and trans-cinnamic acid on inhibition of root elongation in lettuce seedling growth bioassays.

A bicyclic sesquiterpene dialdehyde, polygodial did not inhibit root elongation up to a concentration of 12.5 microg/ml in a lettuce seedling assay: trans-Cinnamic acid inhibited the elongation by 50% at 1.2 microg/ml (8.1 microM). The inhibitory activity of trans-cinnamic acid was enhanced 17-fold when used in combination with 6.25 microg/ml (26.5 microM) of polygodial. A decrease in the pH of the medium was observed during normal seedling growth, indicating transport of protons from the cells by a plasma membrane H+-ATPase. The inhibitory effect of trans-cinnamic acid on the elongation was reduced to some extent in 2 mM phosphate buffer (pH 7.0) during seedling growth. Although polygodial did not inhibit the activity of H+-ATPase in the plasma membrane fraction of roots in normally growing seedlings, a decrease in activity was found in the fraction obtained from seedlings incubated with 20 microg/ml of polygodial. These results suggest that polygodial functions synergistically with trans-cinnamic acid in the inhibition of root elongation via restriction of proton transport from the cytoplasm of germinated cells.

Assessment of toxicity reduction after metal removal in bioleached sewage sludge

Sewage sludge can be applied to land to supply and recycle organic matter and nutrients. Trace elements in sludge, however, may accumulate in the soil with repeated sludge applications. Reducing metal content may therefore reduce the adverse effects of sludge application. The objective of this study was to evaluate the efficiency of bioleaching technology in reducing metal content and toxicity as measured by a battery of terrestrial and liquid-phase bioassays. Sludge–soil mixtures simulating the application of sludge to land were tested by means of terrestrial bioassays, barley ( Hordeum vulgare L.) seed germination (5 d) and sprout growth (14 d), lettuce ( Lactuca sativa) seed germination (5 d), and worm ( Eisenia andrei) mortality (14 d). Liquid-phase bioassays, Microtox ® ( Vibrio fischeri, 15 min), lettuce root elongation ( L. sativa, 5 d), cladoceran mortality ( Daphnia magna, 48 h), and SOS Chromotest ( Escherichia coli) were used after elutriation of the sludge. Comparison of the bioassay results (except for D. magna) before and after treatment demonstrated that this bioleaching process reduced both sludge toxicity and metal content. In addition, lower Cu and Zn concentrations found in barley sprouts following treatment supported the assumption that the bioleaching process, by decreasing metal content and bioavailability, reduced sewage sludge toxicity. This study also emphasized the interest of using ecotoxicological bioassays for testing biosolids. In particular, the terrestrial bioassays after simulation of land application and the Microtox ® test after sludge elutriation proved to be the most appropriate procedures.

Purification of alginate oligosaccharides with root growth-promoting activity toward lettuce.

Sodium alginate was degraded by alginate lyase from Corynebacterium sp., and the product was purified by an ultrafiltration (UF) membrane module. The UF treatment was carried out at a transmembrane pressure of 0.15 MPa and a flow velocity of 0.6 m/s in the cross-flow mode, and non-degraded alginate was almost completely removed. The alginate oligosaccharide obtained was a mixture of di- to octasaccharides and had promoting activity toward lettuce root elongation (about 2-fold compared with the control) in the concentration range of 200-3000 microg/ml. The effect of the degree of polymerization on this activity was examined by using each oligosaccharide fractionated by gel chromatography. The tri-, tetra-, penta- and hexasaccharides were each found to have root growth-promoting activity in a lettuce bioassay.

Procedure to Screen Illicit Discharge of Toxic Substances in Septic Sludge Received at a Wastewater Treatment Plant

This paper presents an integrative approach, using toxicological and chemical analyses, to screen toxic and illegal substances that could be added to the septic sludge transported by a tanker truck to the wastewater treatment plant of the Montreal Urban Community (MUC). Microtox, lettuce root elongation, and a bacterial respiration test were used to establish the toxicity range of a normal sludge and the determination of threshold limit criteria. Septic sludge samples were spiked with different types and amounts of contaminants (copper, zinc, phenol, industrial sludge). Conservative criteria were applied to detect abnormal toxicity with great reliability while avoiding false positives (i.e., detecting abnormal toxicity in nonspiked sludge). Taken individually, toxicity tests using Microtox were revealed to be the least discriminating toxicological method (efficiency of 45% when the ratio of the IC50values is considered), whereas lettuce root elongation was relatively the most efficient (80% of spiked samples). As a whole, the battery of toxicity tests detected at least 93% of the spiked sludge samples. This procedure is also very efficient, i.e., easy to apply, cost effective, and rapid. In certain cases, an abnormal toxicity level can be determined within a few hours, whereas a septic sludge can be classified as normal within 5 days.

Use of plant and earthworm bioassays to evaluate remediation of soil from a site contaminated with polychlorinated biphenyls

AbstractSoil from a site heavily contaminated with polychlorinated biphenyls (PCBs) was treated with a pilot‐scale, solvent extraction technology. Bioassays in earthworms and plants were used to examine the efficacy of the remediation process for reducing the toxicity of the soil. The earthworm toxicity bioassays were the 14‐d survival test and 21‐d reproduction test, using Lumbricus terrestris and Eisenia fetida andrei. The plant bioassays included phytotoxicity tests for seed germination and root elongation in lettuce and oats, and a genotoxicity test (anaphase aberrations) in Allium cepa (common onion). Although the PCB content of the soil was reduced by 99% (below the remediation goal), toxicity to earthworm reproduction remained essentially unchanged following remediation. Furthermore, phytotoxicity and genotoxicity were higher for the remediated soil compared to the untreated soil. The toxicity remaining after treatment appeared to be due to residual solvent introduced during the remediation process, and/or to heavy metals or other inorganic contaminants not removed by the treatment. Mixture studies involving isopropanol and known toxicants indicated possible synergistic effects of the extraction solvent and soil contaminants. The toxicity in plants was essentially eliminated by a postremediation, water‐rinsing step. These results demonstrate a need for including toxicity measurements in the evaluation of technologies used in hazardous waste site remediations, and illustrate the potential value of such measurements for making modifications to remediation processes.

Automated Recording of Lettuce Root Elongation as Affected by Auxin and Acid pH in A New Rhizometer with Minimum Mechanical Contact to Roots

Automated Recording of Lettuce Root Elongation as Affected by Auxin and Acid pH in A New Rhizometer with Minimum Mechanical Contact to Roots

Roots of Sorghum Exude Hydrophobic Droplets Containing Biologically Active Components1

Roots of Sorghum are known to exude materials that exhibit allelochemical activity, but the compounds identified do not completely account for the observed species‐specific allelochemical activities. The purpose of this investigation was to characterize both water‐soluble and water‐insoluble exudates from roots of sorghum [Sorghum bicolor (L.) Moench] seedlings grown in petri dishes. Hydrophilic exudates included phenols, protein, and 3‐deoxyanthocyanidin derivatives. Hydrophobic droplets, exuded from root hairs, tested positively for phenols and lipids. These hydrophobic exudates strongly inhibit (85%) root elongation in lettuce (Lactuca sativa cv. Great Lakes) seedlings, but do not affect that of corn (Zea mays L. cv. B73Ht), nor the germination of either of these plants. Associated with these hydrophobic droplets are novel quinones, yet unidentified. The results indicate that these hydrophobic exudate droplets contain components that may have species‐specific biological activities.

Changes in biological activity of sodium humate as induced by the mercury discharge tube radiation

The study was concerned with the effects of irradiation of the sodium humate on its biological activity, which was assessed by the elongation of the hypocotyl and root in young plants of lettuce (Lactuca sativa L. cv. Rapid and cv. Smaragd) growing in the solution of the tested preparation. It was found that its stimulative action on hypocotyl and root elongation in lettuce was changed due to irradiation. However, the degree was dependent on concentration; stimulation mostly decreased, only at some higher concentrations did it increase. Further, experiments showed that there was some interaction between the irradiation of the humate and the cultivar used for testing, but none between the irradiation and the light exposure of plants during the test. The response of the experimental plants to the concentration of the humate depends on the light exposure.

Inhibition of Lettuce Seed Germination and Root Elongation by Derivatives of Auxin and Reversal by Derivatives of Cycocel

AbstractLettuce seed germination or lettuce root elongation after germination in water was inhibited by 5.7 × 10‐6M indoleacetic acid (IAA) and designated other IAA derivatives. These IAA‐inhibited growth responses were reversed by 10‐5 to 10‐6M Cycocel, (2‐chloroethyl) trimethylammonium chloride, which alone was without effect. Only those Cycocel analogs, which have previously been shown to be active as plant growth retardants, were effective in reversing IAA inhibition of germination or root elongation. These results are consistent with the concept that Cycocel at low concentrations acts as an auxin antagonist. However. Cycocel did not reverse the inhibitory effects from indole‐3‐propionic acid or indole‐3‐butyric acid.

Light‐controlled Cycocel Reversal of Coumarin Inhibition of Lettuce Seed Germination and Root Growth

AbstractLettuce seed germination or lettuce root elongation after germination in water was inhibited by coumarin and these inhibitions were reversed by Cycocel. 2.53 × 103 M Cycocel reversed the inhibition of seed germination by 6.8 × 104 M coumarin. and 6.32 × lO−4 M Cycocel reversed the inhibition of root elongation by 3.4 × 103 M coumarin. No other analogs of Cycocel reversed these coumarin induced inhibitions of growth. Cycocel reversal of coumarin inhibition of lettuce seed germination occurred in red light but not in far‐red light or darkness. The red‐far‐red system was photoreversible. Cycocel and kinetin appear to act similarly in reversing coumarin inhibition of germination. Gibberellin A3 and IAA were unable to reverse these coumarin induced inhibitions. A common mechanism is suggested for Cycocel reversal of coumarin and lAA inhibition of growth.