The metabolic response of plants to exogenous supply and bioaccumulation of trivalent chromium (Cr(3+) ) was investigated. Pre-rooted young hybrid willows (Salix matsudana Koidz x alba L.) were exposed to hydroponic solution spiked with CrCl(3) at 24.0 degrees C +/- 1 degrees C for 192 hours. Various physiologic parameters of the plants were monitored to determine toxicity from Cr exposure. The transpiration rate of willows exposed to 2.5 mg Cr/L was 49% higher than that of the untreated control plants, but it was decreased by 17% when exposed to 30.0 mg Cr/L. Significant decrease (> or =20%) of soluble protein in young leaves of willows was detected in the treatment group with > or =7.5 mg Cr/L. The measured chlorophyll contents in leaves of treated plants varied with the dose of Cr, but a linear correlation could not be established. The contents of chlorophyll in leaves of willows exposed to > or =7.5 mg Cr/L were higher than that of the untreated plants but lower at 30.0 mg Cr/L. Superoxide dismutase activity (SOD) in leaves between the treated and untreated willows did not show any significant difference, but activities of both catalase (CAT) and peroxidase (POD) in leaf cells of all treated plants were higher than those in the untreated willows. The correlation between the concentration of Cr and CAT activity in leaf cells was the highest of all toxicity assays (R ( 2 ) = 0.9096), indicating that CAT activity was most sensitive to the change in Cr(3+) doses compared with the other selected parameters. Results from the Cr uptake study showed that significant removal of Cr from hydroponic solution was observed in the presence of hybrid willows without showing detectable phytotoxicity, even at high does of Cr. More than 90% of the applied Cr(3+) was removed from the aqueous solution by willows at concentrations up to 7.5 mg Cr/L. Approximately 70% of the initial Cr was recovered in the plant materials. At the low-Cr(3+) treatment (2.5 mg Cr/L), Cr accumulation by willow materials was the greatest (92%) in roots and the lowest (0.2%) in leaves, whereas the greatest (66%) was in stems and the lowest (0.1%) in leaves of willows exposed to 30.0 mg Cr/L. The correlation between applied Cr(3+) (mg Cr/L) and Cr (mug Cr/g fresh weight [fw]) accumulated in plant materials was significant. The bioaccumulation kinetics of Cr by hybrid willows can be described by a typical saturation curve. Results also indicated that translocation of Cr from roots to shoots was possible. It is to conclude that hybrid willows have great potential as bioremediation technology in the removal of chromium (Cr(3+)) from contaminated effluents and sediments.
Cyanide is a simple nitrogenous compound that arises from both anthropogenic and natural sources. Plants vary considerably in their physiological and biochemical responses to different species of exogenous cyanides from reduced growth to inhibition on enzymatic activities. Also, great differences in uptake, assimilation and toxicity between free cyanide and iron cyanide have been observed. Unlike botanical uptake of free cyanide chiefly achieved by simple diffusion, iron cyanides have long been considered membrane impermeable and a protein-mediated uptake mode has been proposed. Biological fate of cyanides in plant materials is highly dependent on speciation of cyanides present. Natural development of degradation of free cyanide in plants is very obvious, where the b-cyanoalanine pathway has been widely distributed in higher plants and the production of asparagine and aspartate associated with cyanide assimilation is suggestive. Because phytodissociation of iron cyanides into free cyanide in plant materials is not a mandatory process involved in phytoassimilation, plants probably metabolized them through an undiscovered degradation pathway rather than the b-cyanoalanine pathway. Available information shows phytoassimilation of endogenous cyanide into nitrogen metabolism; however, additional efforts to fully elucidate presence of essential enzymes involved and their proteomic or DNA expression quantitatively are needed to prove and clarify phyto-benefits of assimilation of exogenous cyanide in plant nutrition.
The ability of maize to remove iron cyanides has important implications on the vegetation management of environmental contamination.
Metabolic responses to hexavalent chromium (Cr(6+)) stress and the uptake and translocation of Cr(6+ )were investigated using pre-rooted hybrid willows (Salix matsudana Koidz x Salix alba L.) exposed to hydroponic solution spiked with K(2)CrO(4) at 24.0 +/- 1 degrees C for 192 h. Various physiological parameters of the plants were monitored to determine toxicity from Cr(6+ )exposure. At Cr(6+) treatments of
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