Showing papers by "Ilya Raskin published in 1995"

Phytoremediation: A Novel Strategy for the Removal of Toxic Metals from the Environment Using Plants

Abstract: Toxic metal pollution of waters and soils is a major environmental problem, and most conventional remediation approaches do not provide acceptable solutions. The use of specially selected and engineered metal-accumulating plants for environmental clean-up is an emerging technology called phytoremediation. Three subsets of this technology are applicable to toxic metal remediation: (1) Phytoextraction--the use of metal-accumulating plants to remove toxic metals from soil; (2) Rhizofiltration--the use of plant roots to remove toxic metals from polluted waters; and (3) Phytostabilization--the use of plants to eliminate the bioavailability of toxic metals in soils. Biological mechanisms of toxic metal uptake, translocation and resistance as well as strategies for improving phytoremediation are also discussed.

Phytoextraction: The Use of Plants To Remove Heavy Metals from Soils

Abstract: A small number of wild plants which grow on metal contaminated soil accumulate large amounts of heavy metals in their roots and shoots This property may be exploited for soil reclamation if an easily cultivated, high biomass crop plant able to accumulate heavy metals is identified Therefore, the ability of various crop plants to accumulate Pb in shoots and roots was compared While all crop Brassicas tested accumulated Pb, some cultivars of Brassica juncea (L) Czern showed a strong ability to accumulate Pb in roots and to transport Pb to the shoots (1083 mg Pb/g DW in the roots and 345 mg Pb/g DW in the shoots) B juncea was also able to concentrate Cr{sup -6}, Cd, Ni, Zn, and Cu in the shoots 58, 52, 31, 17, and 7 fold, respectively, from a substrate containing sulfates and phosphates as fertilizers The high metal accumulation by some cultivars of B juncea suggests that these plants may be used to clean up toxic metal-contaminated sites in a process termed phytoextraction

Mechanisms of Cadmium Mobility and Accumulation in Indian Mustard

Abstract: Indian mustard (Brassica juncea L.), a high biomass crop plant, accumulated substantial amounts of cadmium, with bioaccumulation coefficients (concentration of Cd in dry plant tissue/concentration in solution) of up to 1100 in shoots and 6700 in roots at nonphytotoxic concentrations of Cd (0.1 [mu]g/mL) in solution. This was associated with a rapid accumulation of phytochelatins in the root, where the majority of the Cd was coordinated with sulfur ligands, probably as a Cd-S4 complex, as demonstrated by x-ray absorption spectroscopy. In contrast, Cd moving in the xylem sap was coordinated predominantly with oxygen or nitrogen ligands. Cd concentrations in the xylem sap and the rate of Cd accumulation in the leaves displayed similar saturation kinetics, suggesting that the process of Cd transport from solution through the root and into the xylem is mediated by a saturable transport system(s). However, Cd translocation to the shoot appeared to be driven by transpiration, since ABA dramatically reduced Cd accumulation in leaves. Within leaves, Cd was preferentially accumulated in trichomes on the leaf surface, and this may be a possible detoxification mechanism.

Rhizofiltration: The Use of Plants to Remove Heavy Metals from Aqueous Streams

Abstract: Heavy metal pollution of water is a major environmental problem facing the modern world. Rhizofiltration - the use of plant roots to remove heavy metals from water is an emerging environmental clean-up technology. Roots of many hydroponically grown terrestrial plants e.g. Indian mustard, sunflower (Hefianthus annuus L.) and various grasses effectively removed toxic metals such as CU{sup -2}, Cd{sup +2}Cr{sup +6}, Ni{sup +2}Pb{sup +2} and Zn{sup +2} from aqueous solutions. Roots of B. juncea concentrated these metals 131 to 563-fold (on a DW basis) above initial solution concentrations. Pb removal was based on tissue absorption and on root-mediated Pb precipitation in the form of insoluble inorganic compounds, mainly Pb phosphate. At high Pb concentrations precipitation played a progressively more important role in Pb removal than tissue absorption, which saturated at approximately 100 {mu}g Pb/g DW root. Dried roots were much less effective than live roots in accumulating Pb and in removing Pb from the solution.

Hydrogen Peroxide Stimulates Salicylic Acid Biosynthesis in Tobacco

Abstract: Hydrogen peroxide induced the accumulation of free benzoic acid (BA) and salicylic acid (SA) in tobacco (Nicotiana tabacum L. cv Xanthi-nc) leaves. Six hours after infiltration with 300 mM H2O2, the levels of BA and SA in leaves increased 5-fold over the levels detected in control leaves. The accumulation of BA and SA was preceded by the rapid activation of benzoic acid 2-hydroxylase (BA2H) in the H2O2-infiltrated tissues. This enzyme catalyzes the formation of SA from BA. Enzyme activation could be reproduced in vitro by addition of H2O2 or cumene hydroperoxide to the assay mixture. H2O2 was most effective in vitro when applied at 6 mM. In vitro activation of BA2H by peroxides was inhibited by the catalase inhibitor 3-amino-1,2,4-triazole. We suggest that H2O2 activates SA biosynthesis via two mechanisms. First, H2O2 stimulates BA2H activity directly or via the formation of its substrate, molecular oxygen, in a catalase-mediated reaction. Second, higher BA levels induce the accumulation of BA2H protein in the cells and provide more substrate for this enzyme.

Salicylic Acid in Rice (Biosynthesis, Conjugation, and Possible Role).

Abstract: Salicylic acid (SA) is a natural inducer of disease resistance in some dicotyledonous plants Rice seedlings (Oryza sativa L) had the highest levels of SA among all plants tested for SA content (between 001 and 3719 [mu]g/g fresh weight) The second leaf of rice seedlings had slightly lower SA levels than any younger leaves To investigate the role of SA in rice disease resistance, we examined the levels of SA in rice (cv M-201) after inoculation with bacterial and fungal pathogens SA levels did not increase after inoculation with either the avirulent pathogen Pseudomonas syringae D20 or with the rice pathogens Magnaporthe grisea, the causal agent of rice blast, and Rhizoctonia solani, the causal agent of sheath blight However, leaf SA levels in 28 rice varieties showed a correlation with generalized blast resistance, indicating that SA may play a role as a constitutive defense compound Biosynthesis and metabolism of SA in rice was studied and compared to that of tobacco Rice shoots converted [14C]cinnamic acid to SA and the lignin precursors p-coumaric and ferulic acids, whereas [14C]benzoic acid was readily converted to SA The data suggest that in rice, as in tobacco, SA is synthesized from cinnamic acid via benzoic acid In rice shoots, SA is largely present as a free acid; however, exogenously supplied SA was converted to [beta]-O-D-glucosylSA by an SA-inducible glucosyltransferase (SA-GTase) A 7-fold induction of SA-GTase activity was observed after 6 h of feeding 1 mM SA Both rice roots and shoots showed similar patterns of SA-GTase induction by SA, with maximal induction after feeding with 1 mM SA

Biosynthesis and metabolism of salicylic acid.

Abstract: Pathways of salicylic acid (SA) biosynthesis and metabolism in tobacco have been recently identified. SA, an endogenous regulator of disease resistance, is a product of phenylpropanoid metabolism formed via decarboxylation of trans-cinnamic acid to benzoic acid and its subsequent 2-hydroxylation to SA. In tobacco mosaic virus-inoculated tobacco leaves, newly synthesized SA is rapidly metabolized to SA O-beta-D-glucoside and methyl salicylate. Two key enzymes involved in SA biosynthesis and metabolism: benzoic acid 2-hydroxylase, which converts benzoic acid to SA, and UDPglucose:SA glucosyltransferase (EC 2.4.1.35), which catalyzes conversion of SA to SA glucoside have been partially purified and characterized. Progress in enzymology and molecular biology of SA biosynthesis and metabolism will provide a better understanding of signal transduction pathway involved in plant disease resistance.

Is Salicylic Acid a Translocated Signal of Systemic Acquired Resistance in Tobacco

Abstract: Salicylic acid (SA) is a likely endogenous signal in the development of systemic acquired resistance (SAR) in some dicotyledonous plants In tobacco mosaic virus (TMV)-resistant Xanthi-nc tobacco, SA levels increase systemically following the inoculation of a single leaf with TMV To determine the extent to which systemic increases in SA result from SA export from the inoculated leaf, SA produced in TMV-inoculated or healthy leaves was noninvasively labeled with 18O2 Spatial and temporal distribution of 18O-SA indicated that most of the SA detected in the healthy tissues was synthesized in the inoculated leaf No significant increase in the activity of benzoic acid 2-hydroxylase, the last enzyme involved in SA biosynthesis, was detected in upper uninoculated leaves, although the basal level of enzyme activity was relatively high No increases in SA level, pathogenesis-related PR-1 gene expression, or TMV resistance in the upper uninoculated leaf were observed if the TMV-inoculated leaf was detached up to 60 hr after inoculation Apart from the inoculated tissues, the highest increase in SA was observed in the leaf located directly above the inoculated leaf The systemic SA increase observed during SAR may be explained by phloem transport of SA from the inoculation sites

Benzoic acid 2-hydroxylase, a soluble oxygenase from tobacco, catalyzes salicylic acid biosynthesis.

Abstract: Benzoic acid 2-hydroxylase (BA2H) catalyzes the biosynthesis of salicylic acid from benzoic acid. The enzyme has been partially purified and characterized as a soluble protein of 160 kDa. High-efficiency in vivo labeling of salicylic acid with 18O2 suggested that BA2H is an oxygenase that specifically hydroxylates the ortho position of benzoic acid. The enzyme was strongly induced by either tobacco mosaic virus inoculation or benzoic acid infiltration of tobacco leaves and it was inhibited by CO and other inhibitors of cytochrome P450 hydroxylases. The BA2H activity was immunodepleted by antibodies raised against SU2, a soluble cytochrome P450 from Streptomyces griseolus. The anti-SU2 antibodies immunoprecipitated a radiolabeled polypeptide of around 160 kDa from the soluble protein extracts of L-[35S]-methionine-fed tobacco leaves. Purified BA2H showed CO-difference spectra with a maximum at 457 nm. These data suggest that BA2H belongs to a novel class of soluble, high molecular weight cytochrome P450 enzymes.

Chilling-Induced Heat Evolution in Plants.

Abstract: Increases in respiration, particularly via the alternative pathway, are observed in response to chilling. These increases result in increased heat evolution. We have measured increases in heat evolution in response to chilling in a number of plant species using a microcalorimeter. After 8 h of exposure to 8[deg]C, heat evolution in a variety of chilling-sensitive species increased 47 to 98%. No increase in heat evolution was seen with the extremely chilling-sensitive ornamental Episcia cupreata Hook. Heat evolution increased only 7 to 22% in the chilling-resistant species. Increases in heat evolution were observed when plants were chilled in constant light or in the dark, but not when plants were chilled at high humidity. Increased capacity to produce respiratory heat after exposure to chilling temperatures may contribute to the cold-acclimation process.

Microbial isolates promote phytoremediation

Abstract: Methods and compositions or enhancing metal uptake of plants, such as members of the family Brassicaceae, comprise treating the roots, plants, seeds, and/or soil in which the plants are grown, with metal-uptake altering microorganisms, preferably of the bacterial genus Pseudomonas and Bacillus.

Jasmonates, Salicylic acid and Brassinosteroids

Abstract: Until recently jasmonic acid (JA) and its fragrant methyl ester, methyl jasmonate (MeJA), had been studied only modestly since their discovery in plants over 30 years ago. Early research focused primarily on their potential role in plant growth and development. However, after jasmonate was shown to increase the expression of genes involved in plant defense, there was a surge in activity aimed at clarifying the function of these potentially important signaling molecules. Although considerable work remains, increasing evidence supports the hypothesis that jasmonate is involved in signaling stress responses in plants.

Biosynthesis, Conjugation, and Possible Role

Abstract: Salicylic acid (SA) is a natural inducer of disease resistance in some dicotyledonous plants. Rice seedlings (Oryza sativa L.) had the highest levels of SA among all plants tested for SA content (between 0.01 and 37.19 ,ug/g fresh weight). The second leaf of rice seedlings had slightly lower SA levels than any younger leaves. To investigate the role of SA in rice disease resistance, we examined the levels of SA in rice (cv M-201) after inoculation with bacterial and fungal pathogens. SA levels did not increase after inoculation with either the avirulent pathogen Pseudomonas syringae D20 or with the rice pathogens Magnaporthe grisea, the causal agent of rice blast, and Rhizoctonia solani, the causal agent of sheath blight. However, leaf SA levels in 28 rice varieties showed a correlation with generalized blast resistance, indicating that SA may play a role as a constitutive defense compound. Biosynthesis and metabolism of SA in rice was studied and compared to that of tobacco. Rice shoots converted ['4C]cinnamic acid to SA and the lignin precursors p-coumaric and ferulic acids, whereas ['4Clbenzoic acid was readily converted to SA. The data suggest that in rice, as in tobacco, SA is synthesized from cinnamic acid via benzoic acid. In rice shoots, SA is largely present as a free acid; however, exogenously supplied SA was converted to P-0-D-glucosylSA by an SA-inducible glucosyltransferase (SA-GTase). A 7-fold induction of SA-GTase activity was observed after 6 h of feeding 1 mm SA. Both rice roots and shoots showed similar patterns of SA-GTase induction by SA, with maximal induction after feeding with 1 mm SA.