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Published on May 12, 2006; 10.1104/pp.105.076240

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Received December 23, 2005
Returned for revision March 13, 2006
Accepted May 2, 2006

Heavy metal stress and sulfate uptake in maize (Zea mays L.) roots

Fabio F Nocito , Clarissa Lancilli , Barbara Crema , Pierre Fourcroy , Jean-Claude Davidian , and Gian Attilio Sacchi *

Dipartimento di Produzione Vegetale, Università degli Studi di Milano, Via Celoria 2, 20133 Milano, Italy; Biochimie & Physiologie Moléculaire des Plantes, Institut National de la Recherche Agronomique (Unité 386), Centre National de la Recherche Scientifique (UMR 5004), Ecole Nationale Supérieure Agronomique de Montpellier, Université Montpellier 2, Place Viala, 34060 Montpellier, cedex 1, France

* Corresponding author; email: gianattilio.sacchi{at}unimi.it.

ZmST1;1, a putative high-affinity sulfate transporter gene expressed in maize (Zea mays L.) roots, was functionally characterized and its expression patterns were analyzed in roots of plants exposed to different heavy metals (Cd, Zn and Cu) interfering with thiol metabolism. The ZmST1;1 cDNA was expressed in the Saccharomyces cerevisiae sulfate transporter mutant CP154-7A. Kinetic analysis of sulfate uptake isotherm, determined on complemented yeast cells, revealed that ZmST1;1 has a high affinity for sulfate (Km value of 14.6 ± 0.4 µM). Cd, Zn and Cu exposure increased both ZmST1;1 expression and root sulfate uptake capacity. The metal-induced sulfate uptakes were accompanied by deep alterations in both thiol metabolism and levels of compounds, such as reduced glutathione (GSH), probably involved as signals in sulfate uptake modulation. Cd and Zn exposure strongly increased the level of non protein thiols (NPTs) of the roots, indicating the induction of additional sinks for reduced sulfur, but differently affected root GSH contents, that decreased or increased following Cd or Zn stress respectively. Moreover, during Cd stress a clear relation between the ZmST1;1 mRNA abundance increment and the entity of the GSH decrement was impossible to evince. Conversely, Cu stress did not affect NPT levels, but resulted in a deep contraction of GSH pools. Our data suggest that during heavy metal stress sulfate uptake by roots may be controlled by both GSH-dependent or -independent signalling pathways. Finally some evidences suggesting that root sulfate availability in Cd stressed plants may limit GSH biosynthesis and thus Cd tolerance are discussed.




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