Full Length Research Paper

Calcium enhances cadmium tolerance and decreases cadmium accumulation in lettuce (Lactuca sativa)

Walid Zorrig^1,2*, Zaigham Shahzad^1,3, Chedly Abdelly² and Pierre Berthomieu¹

¹Biochimie and Physiologie Moléculaire des Plantes, Unité Mixte de Recherche CNRS-INRA-Université Montpellier II-Montpellier supagro, Place Viala, 34060 Montpellier Cédex 2, France.

²Laboratoire des Plantes Extrêmophiles, Centre de Biotechnologie, BP 901, Hammam-Lif 2050, Tunisie.

³Department of Plant Breeding and Genetics, University of Agriculture, Faisalabad, Pakistan.

*Corresponding author. E-mail: zorrigwalid@yahoo.fr. Tel : 00216 22 177 081. Fax: 00216 79 412 948.

Accepted 4 November, 2011

   Abstract

We aimed at characterizing mechanisms controlling cadmium accumulation in lettuce, which is a food crop showing one of the highest capacities to accumulate this toxic compound. In this study, plants from three lettuce varieties were grown for eight days on media supplemented or not with cadmium (15 µM CdCl₂) and containing different concentrations of calcium (0.5, 1, 2.5, 5 and 10 mM Ca(NO₃)₂). Our results show that exposure to cadmium resulted in biomass reduction. The biomass reduction was particularly high at 0.5 mM calcium but supplementation of the medium with increasing calcium concentrations alleviated the toxic effect of cadmium on the growth and water status of lettuce plants. The three lettuce varieties displayed different abilities to accumulate cadmium. Interestingly, increasing the calcium concentration in the medium resulted in a strong decrease in cadmium contents. These results suggest that cadmium uptake in lettuce plants is negatively associated with the presence of calcium in the culture medium, maybe due to a competition between these two cations for binding and absorption sites in roots. In conclusion, the results suggest that fertilization with Ca²⁺ appears to be a promising strategy for decreasing risk associated with ingesting food crops grown on cadmium polluted soils.

Key words: Lettuce, food security, growth, cadmium accumulation, cadmium translocation, calcium.