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Root Elongation (root + elongation)
Selected AbstractsIdentification of hydroxyl copper toxicity to barley (Hordeum vulgare) root elongation in solution cultureENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2009Xuedong Wang Abstract The effect of pH on the acute toxicity of Cu to barley (Hordeum vulgare) root elongation was investigated in solution culture. The results showed that the median effective concentrations (EC50s; i.e., the concentration that reduced root elongation by 50% based on free Cu2+ activity) were not significantly different in the low-pH range from 4.5 to 6.5, but in the high-pH range from 7.0 to 8.0, a significant effect of pH on EC50s was found. The nonlinear relationship between EC50 and H+ activity in the present study indicated that the increased toxicity with increasing pH in solution may not be caused by decreasing H+ competition. When we take account of CuOH+ activities, a good linear relationship (r2 > 0.97) between the ratio of CuOH+ activity to free Cu2+ activity and acute Cu toxicity to barley root elongation was achieved, which indicated that the observed toxicity in the high-pH range may be caused by CuOH+ plus free Cu2+ in solution. Linear-regression analysis suggested CuOH+ had a greater binding affinity than Cu2+ at the biotic ligand sites. The logistic dose,response curve showed that expressing the Cu dose as Cu2+ + 2.92·CuOH+ improved the data fit significantly compared to consideration of the free Cu2+ activity only. Thus, our results suggest CuOH+ was highly toxic to barley root elongation. The enhanced toxicity of CuOH+ therefore needs to be considered when modeling the effect of pH on Cu toxicity to barley for exposures having pH greater than 6.5. [source] Effects of functionalized and nonfunctionalized single-walled carbon nanotubes on root elongation of select crop species,,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 9 2008Jaclyn E. Cañas Abstract 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-aminoben-zenesulfonic 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. [source] The significance of organic-anion exudation for the aluminum resistance of primary triticale derived from wheat and rye parents differing in aluminum resistanceJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 4 2008Angelika Stass Abstract Eight primary octoploid triticale genotypes (xTriticosecale Wittmack) derived from four wheat cultivars (Triticum aestivum L.) and two rye inbred lines (Secale cereale L.) differing in aluminum (Al) resistance were investigated with respect to their response to Al supply. Aluminum-induced inhibition of root elongation (48 h, 25 µM Al supply), callose formation, and the accumulation of Al in root tips (4 h, 25 µM Al supply) were used as parameters to assess Al resistance. Using these parameters, the existing information on Al resistance of the wheat and rye cultivars was generally confirmed. The triticale cultivars showed a wide range of Al resistance amongst the Al-sensitive wheat and the Al-resistant rye cultivars. The rye parents and the Al-resistant wheat parent Carazinho were characterized by Al-induced exudation particularly of citrate but also of malate from whole root systems of 14 d old seedlings (8 h, 50 µM Al supply). Regression analysis revealed that the degree of Al resistance of the triticale genotypes was closely related to the Al-induced citrate exudation, which was mainly controlled by the Al resistance of the wheat parent. [source] Citrate exudation from white lupin induced by phosphorus deficiency differs from that induced by aluminumNEW PHYTOLOGIST, Issue 3 2007B. L. Wang Summary ,,Both phosphorus (P) deficiency and aluminum (Al) toxicity induce root exudation of carboxylates, but the relationship between these two effects is not fully understood. Here, carboxylate exudation induced by Al in Lupinus albus (white lupin) was characterized and compared with that induced by P deficiency. ,,Aluminum treatments were applied to whole root systems or selected root zones of plants with limited (1 µm) or sufficient (50 µm) P supply. ,,Aluminum stimulated citrate efflux after 1,2 h; this response was not mimicked by a similar trivalent cation, La3+. P deficiency triggered citrate release from mature cluster roots, whereas Al stimulated citrate exudation from the 5- to 10-mm subapical root zones of lateral roots and from mature and senescent cluster roots. Al-induced citrate exudation was inhibited by P limitation at the seedling stage, but was stimulated at later growth stages. Citrate exudation was sensitive to anion-channel blockers. Al treatments did not affect primary root elongation, but inhibited the elongation of lateral roots. ,,The data demonstrate differential patterns of citrate exudation in L. albus, depending on root zone, developmental stage, P nutritional status and Al stress. These findings are discussed in terms of possible functions and underlying mechanisms. [source] Effect of boron on the expression of aluminium toxicity in Phaseolus vulgarisPHYSIOLOGIA PLANTARUM, Issue 2 2007Angelika Stass The interaction of boron (B) and aluminium (Al) was investigated in 5-day-old seedlings of soybean cv. Maple Arrow. Al treatment inhibited root elongation and callose formation in root tips particularly after 4-h Al treatment. After 10 and 24 h, both parameters indicated increasing recovery from Al stress. B deficiency aggravated Al toxicity compared with B sufficiency. B deficiency did lead to an increase in unmethylated pectin in the first 3 mm of the root tip. This increase in potential binding sites is reflected in generally higher Al contents in root tips of B-deficient plants. A fractionated extraction of Al from the root tips showed that citrate-exchangeable and non-exchangeable Al steeply increased up to 4 h, but then decreased after 10- and 24-h Al treatment faster in B-sufficient than in B-deficient plants. This decrease of Al contents can be explained by an Al-enhanced release of citrate from the root tips after 10-h Al treatment. However, the citrate exudation rate was the same (after 10 h) or even lower (after 24 h) in B-sufficient plants and thus cannot explain the faster decrease in Al contents of the root tips compared with the B-deficient plants. We, therefore, propose that under B deficiency, Al is more strongly bound by the pectic network of the cell wall of the root tips, which delays or prevents the recovery from initial Al stress through exudation of citrate, and thus explains the greater Al sensitivity of B-deficient common bean roots. [source] The mechanism of boron tolerance for maintenance of root growth in barley (Hordeum vulgare L.)PLANT CELL & ENVIRONMENT, Issue 8 2007EUN-YOUNG CHOI ABSTRACT Cultivar differences in root elongation under B toxic conditions were observed in barley (Hordeum vulgare L.). A significant increase in the length and width of the root meristematic zone (RMZ) was observed in Sahara 3771 (B tolerant) when it was grown under excessive B concentration, compared to when grown at adequate B supply. This coincided with an increase in cell width and cell numbers in the meristematic zone (MZ), whereas a significant decrease in the length and no significant effect on the width of the MZ was observed in Clipper (B intolerant) when it was grown under excessive B supply. This was accompanied by a decrease in cell numbers, but an increase in the length and width of individual cells present along the MZ. Excessive B concentrations led to a significantly lower osmotic potential within the cell sap of the root tip in SloopVic (B tolerant) and Sahara 3771, while the opposite was observed in Clipper. Enhanced sugar levels in the root tips of SloopVic were observed between 48 and 96 h after excess B was applied. This coincided with an increase in the root elongation rate and with a 2.7-fold increase in sucrose level within mature leaf tissue. A significant decrease in reducing sugar levels was observed in the root tips of Clipper under excessive B concentrations. This coincided with significantly lower root elongation rates and lower sucrose levels in leaf tissues. Results indicate a B tolerance mechanism associated with a complex control of sucrose levels between leaf and root tip that assist in maintaining root growth under B toxicity. [source] Ethylene regulates lateral root formation and auxin transport in Arabidopsis thalianaTHE PLANT JOURNAL, Issue 2 2008Sangeeta Negi Summary Lateral root branching is a genetically defined and environmentally regulated process. Auxin is required for lateral root formation, and mutants that are altered in auxin synthesis, transport or signaling often have lateral root defects. Crosstalk between auxin and ethylene in root elongation has been demonstrated, but interactions between these hormones in the regulation of Arabidopsis lateral root formation are not well characterized. This study utilized Arabidopsis mutants altered in ethylene signaling and synthesis to explore the role of ethylene in lateral root formation. We find that enhanced ethylene synthesis or signaling, through the eto1-1 and ctr1-1 mutations, or through the application of 1-aminocyclopropane-1-carboxylic acid (ACC), negatively impacts lateral root formation, and is reversible by treatment with the ethylene antagonist, silver nitrate. In contrast, mutations that block ethylene responses, etr1-3 and ein2-5, enhance root formation and render it insensitive to the effect of ACC, even though these mutants have reduced root elongation at high ACC doses. ACC treatments or the eto1-1 mutation significantly enhance radiolabeled indole-3-acetic acid (IAA) transport in both the acropetal and the basipetal directions. ein2-5 and etr1-3 have less acropetal IAA transport, and transport is no longer regulated by ACC. DR5-GUS reporter expression is also altered by ACC treatment, which is consistent with transport differences. The aux1-7 mutant, which has a defect in an IAA influx protein, is insensitive to the ethylene inhibition of root formation. aux1-7 also has ACC-insensitive acropetal and basipetal IAA transport, as well as altered DR5-GUS expression, which is consistent with ethylene altering AUX1-mediated IAA uptake, and thereby blocking lateral root formation. [source] The Arabidopsis her1 mutant implicates GABA in E -2-hexenal responsivenessTHE PLANT JOURNAL, Issue 2 2008Rossana Mirabella Summary When wounded or attacked by herbivores or pathogens, plants produce a blend of six-carbon alcohols, aldehydes and esters, known as C6-volatiles. Undamaged plants, when exposed to C6-volatiles, respond by inducing defense-related genes and secondary metabolites, suggesting that C6-volatiles can act as signaling molecules regulating plant defense responses. However, to date, the molecular mechanisms by which plants perceive and respond to these volatiles are unknown. To elucidate such mechanisms, we decided to isolate Arabidopsis thaliana mutants in which responses to C6-volatiles were altered. We observed that treatment of Arabidopsis seedlings with the C6-volatile E -2-hexenal inhibits root elongation. Among C6-volatiles this response is specific to E -2-hexenal, and is not dependent on ethylene, jasmonic and salicylic acid. Using this bioassay, we isolated 18 E -2-hexenal-response (her) mutants that showed sustained root growth after E -2-hexenal treatment. Here, we focused on the molecular characterization of one of these mutants, her1. Microarray and map-based cloning revealed that her1 encodes a ,-amino butyric acid transaminase (GABA-TP), an enzyme that degrades GABA. As a consequence of the mutation, her1 plants accumulate high GABA levels in all their organs. Based on the observation that E -2-hexenal treatment induces GABA accumulation, and that high GABA levels confer resistance to E -2-hexenal, we propose a role for GABA in mediating E -2-hexenal responses. [source] N -Glucosyl-1H -indole Derivatives from Cortinarius brunneus (Basidiomycetes)CHEMISTRY & BIODIVERSITY, Issue 4 2008Axel Teichert Abstract Two new N -glucosylated indole alkaloids were isolated from fruiting bodies of the basidiomycete Cortinarius brunneus (Pers.) Fr. The structures were elucidated by means of the spectroscopic data. Additionally, the very recently reported compounds N- 1 -,- glucopyranosyl-3-(carboxymethyl)-1H -indole (3) and N- 1 -,- glucopyranosyl-3-(2-methoxy-2-oxoethyl)-1H -indole (4) could be detected. Compound 3 is the N -glucoside of the plant-growth regulator 1H -indole-3-acetic acid (IAA), but, in contrast, it does not exhibit auxin-like activity in an Arabidopsis thaliana tap root elongation assay. [source] Structure Elucidation and Phytotoxicity of Ecdysteroids from Chenopodium albumCHEMISTRY & BIODIVERSITY, Issue 4 2005Marina DellaGreca The leaves of Chenopodium album were infused in H2O/MeOH. The extract treated with cold acetone gave heavy precipitation, which was removed by centrifugation. Solid material was fractionated into acidic and neutral fractions. The acidic material was subjected to different silica-gel column chromatographies, and then it was purified by reversed-phase HPLC to afford four known ecdysteroids and the new 3,,14, -dihydroxy-5, -pregn-7-ene-2,6,20-trione that were characterized by extensive spectroscopic investigation, especially by 1D- and 2D-NMR. Their effects on germination and growth of Lactuca sativa L. have been studied. The results are reported as percentage differences of germination, root elongation and shoot elongation, from the control at concentrations ranging from 10,4 to 10,7,M. [source] Chenoalbicin, a Novel Cinnamic Acid Amide Alkaloid from Chenopodium albumCHEMISTRY & BIODIVERSITY, Issue 10 2004Francesca Cutillo The roots of Chenopodium album were infused in MeOH, and the extract was partitioned between AcOEt and H2O. AcOEt-Soluble material was subjected to different silica-gel column chromatographies and then purified by reverse-phase HPLC to afford a new cinnamic acid amide alkaloid as a racemic mixture. The new compound, named chenoalbicin (1), was characterized by extensive spectroscopic investigation, especially 1D and 2D NMR spectroscopy. Its effects on the germination and growth of Lactuca sativa L. has been studied. The results are reported as percentage differences of germination, root elongation, and shoot elongation from the control at concentrations ranging from 10,4 to 10,7,M. [source] | ||||||||||