First published online July 18, 2002; 10.1104/pp.002659
Plant Physiol, August 2002, Vol. 129, pp. 1872-1879
Cadmium-Induced Sulfate Uptake in Maize
Roots1
Fabio F.
Nocito,
Livia
Pirovano,
Maurizio
Cocucci, and
Gian Attilio
Sacchi*
Dipartimento di Produzione Vegetale, Università degli Studi
di Milano, Via Celoria 2, 20133 Milano, Italy
The effect of cadmium (Cd) on high-affinity sulfate
transport of maize (Zea mays) roots was studied and
related to the changes in the levels of sulfate and nonprotein thiols
during Cd-induced phytochelatin (PC) biosynthesis. Ten micromolar
CdCl2 in the nutrient solution induced a 100% increase in
sulfate uptake by roots. This was not observed either for potassium or
phosphate uptake, suggesting a specific effect of Cd2+ on
sulfate transport. The higher sulfate uptake was not dependent on a
change in the proton motive force that energizes it. In fact, in
Cd-treated plants, the transmembrane electric potential difference of
root cortical cells was only slightly more negative than in the
controls, the external pH did not change, and the activity of the
plasma membrane H+-ATPase did not increase. Kinetics
analysis showed that in the range of the high-affinity sulfate
transport systems, 10 to 250 µM, Cd exposure did not
influence the Km value (about 20 µM), whereas it doubled the
Vmax value with respect to the control. Northern-blot analysis showed that Cd-induced sulfate uptake was related to a higher level of mRNA encoding for a putative high-affinity sulfate transporter in roots. Cd-induced sulfate uptake was associated to both a decrease in the contents of sulfate and glutathione and
synthesis of a large amount of PCs. These results suggest that
Cd-induced sulfate uptake depends on a pretranslational regulation of
the high-affinity sulfate transporter gene and that this
response is necessary for sustaining the higher sulfur demand during PC biosynthesis.
1
This work was supported by the National Research
Council of Italy (Progetto Finalizzato Biotecnologie, Subproject 2, Line 2.1. and CNR-Agenzia 2000, code CNRG00857B).
*
Corresponding author; e-mail gianattilio.sacchi{at}unimi.it; fax
39-02-50316525.
© 2002 American Society of Plant Physiologists
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