Copper-binding proteins and copper tolerance in Pisam sativum L. |
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Authors: | J M Palma J Yáñez M Gómez L A del Río |
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Institution: | (1) Unidad de Bioquimica Vegetal, Estación Experimental del Zaidín, C.S.I.C., Apdo. 419, E-18080 Granada, Spain |
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Abstract: | The effect of high nutrient levels of copper on the low-molecular-weight copper-proteins of leaves from plants of two cultivars of Pisum sativum L., with different sensitivity to copper, was investigated. Gel-filtration chromatography of leaf extracts from Cu-tolerant and Cu-sensitive plants grown with 1 M Cu(II), showed the presence of only two copper peaks (I and II), but growth of plants with 240 M Cu(II) induced two additional copper fractions (III and IV). Fractions II and III were purified by solvent extraction, gel-filtration and ion-exchange chromatography, and their molecular weights, subunit sizes, absorption spectra, metalprotein stoichiometry and amino-acid contents were determined. Fraction II was a polypeptide of Mr 15000 composed of a single chain. The purification of fraction III produced a copper-containing fraction (III-1) of Mr 3700, and a copper-protein (III-2) with an Mr, by sodium dodecyl sulfate-urea-polyacrylamide gel electrophoresis, of 66000. The metal contents of fractions III-1 and III-2 were higher in Cu-tolerant than in Cu-sensitive plants. On the basis of amino-acid analyses, fraction III-1 appeared to be complexes of Cu(II)-poly-isoleucine and Cu(II)-poly-leucine. The results rule out the existence, in pea leaves, of any protein similar to either animal metallothioneins or to any of the low-molecularweight metal-binding proteins or peptides described in other plants and reported to be involved in metal tolerance. In the mechanism of copper tolerance at the leaf level, fractions III-1 (Mr 3700), III-2 (Mr 66000), and IV (Mr 2000) appear to have a role, fraction IV being specifically induced in the tolerant cultivar by Cu(II). Fractions III-1 and III-2 could participate in a different mechanism, adaptive in character, involving an enhanced capacity to bind copper in Cu-tolerant plants.Abbreviations DEAE
diethylaminoethyl
- Mr
relative molecular mass
- SDS
sodium dodecyl sulfate
- PAGE
polyacrylamide-gel electrophoresis
J.M. Palma was the recipient of a research fellowship from the Caja General de Ahorros y Monte de Piedad de Granada and CSIC. We are grateful to Dr. J. Moreno-Carretero, R + D Department, UNIASA, Granada, for conducting the amino-acid analyses. This work was supported by grant 603/275 from CAICYT-CSIC (Spain). |
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Keywords: | Copper-binding protein (characterization) Copper sensitivity tolerance Metal toxicity Pisum (copper tolerance) |
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