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Plant and Cell Physiology Advance Access originally published online on January 30, 2008
Plant and Cell Physiology 2008 49(3):362-374; doi:10.1093/pcp/pcn013
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© The Author 2008. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org

Increase in Ascorbate–Glutathione Metabolism as Local and Precocious Systemic Responses Induced by Cadmium in Durum Wheat Plants

Annalisa Paradiso1, Rosalia Berardino1, Maria C. de Pinto1, Luigi Sanità di Toppi2, Maria M. Storelli3, Franca Tommasi1 and Laura De Gara1,4,*

1Dipartimento di Biologia e Patologia Vegetale, Università degli Studi di Bari, Via E. Orabona, 4, 70125 Bari, Italy
2Dipartimento di Biologia Evolutiva e Funzionale, Università di Parma, Viale G.P. Usberti, 11/A, 43100 Parma, Italy
3Dipartimento Farmaco-Biologico, Università degli Studi di Bari, Strada Prov.le per Casamassima Km 3, 70010, Valenzano (Ba), Italy
4Centro Interdipartimentale di Ricerche Biomediche, Università Campus Bio-Medico, Via Alvaro del Portillo 21, 00128 Roma, Italy

*Corresponding author: E-mail, degara{at}botanica.uniba.it; Fax, +39.080.5443553.


  Abstract

Durum wheat plants (Triticum durum cv Creso) were grown in the presence of cadmium (0–40 µM) and analysed after 3 and 7 d for their growth, oxidative stress markers, phytochelatins, and enzymes and metabolites of the ascorbate (ASC)–glutathione (GSH) cycle. Cd exposure produced a dose-dependent inhibition of growth in both roots and leaves. Lipid peroxidation, protein oxidation and the decrease in the ascorbate redox state indicate the presence of oxidative stress in the roots, where H2O2 overproduction and phytochelatin synthesis also occurred. The activity of the ASC–GSH cycle enzymes significantly increased in roots. Consistently, a dose-dependent accumulation of Cd was evident in these organs. On the other hand, no oxidative stress symptoms or phytochelatin synthesis occurred in the leaves; where, at least during the time of our analysis, the levels of Cd remained irrelevant. In spite of this, enzymes of the ASC–GSH cycle significantly increased their activity in the leaves. When ASC biosynthesis was enhanced, by feeding plants with its last precursor, L-galactono-{gamma}-lactone (GL), Cd uptake was not affected. On the other hand, the oxidative stress induced in the roots by the heavy metal was alleviated. GL treatment also inhibited the Cd-dependent phytochelatin biosynthesis. These results suggest that different strategies can successfully cope with heavy metal toxicity. The changes that occurred in the ASC–GSH cycle enzymes of the leaves also suggest that the whole plant improved its antioxidant defense, even in those parts which had not yet been reached by Cd. This precocious increase in the enzymes of the ASC–GSH cycle further highlight the tight regulation and the relevance of this cycle in the defense against heavy metals.

Keywords: Ascorbate–glutathione cycle - Cadmium - L-Galactono-{gamma}-lactone - Hydrogen peroxide - Oxidative stress - Phytochelatins

Abbreviations: ANOVA, analysis of variance; APX, ascorbate peroxidase; ASC, ascorbate; BSA, bovine seum albumin; DHA, dehydroascorbate; DHAR, dehydroascorbate reductase; DHR123, dihydrorhodamine 123; DNPH, 2,4-dinitrophenylhydrazine; GL, L-galactono-{gamma}-lactone; GR, glutathione reductase; GSH, glutathione; PC, phytochelatin; MDA, monodehydroascorbate; MDAR, monodehydroascorbate reductase; ROS, reactive oxygen species; TBA, thiobarbituric acid.

(Received November 19, 2007; Accepted January 19, 2008)
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