Expression of Genes Involved in Heavy Metal Trafficking in Plants Exposed to Salinity Stress and Elevated Cd Concentrations

Abstract

Many areas intended for crop production suffer from the concomitant occurrence of heavy metal pollution and elevated salinity; therefore, halophytes seem to represent a promising perspective for the bioremediation of contaminated soils. In this study, the influence of Cd treatment (0.01-10.0 mM) and salinity stress (0.4 M NaCl) on the expression of genes involved in heavy metal uptake (<i>irt2</i>-iron-regulated protein 2, <i>zip4</i>-zinc-induced protein 4), vacuolar sequestration (<i>abcc2</i>-ATP-binding cassette 2, <i>cax4</i>-cation exchanger 2 <i>pcs1</i>-phytochelatin synthase 1) and translocation into aerial organs (<i>hma4</i>-heavy metal ATPase 4) were analyzed in a soil-grown semi-halophyte <i>Mesembryanthemum crystallinum</i>. The upregulation of <i>irt2</i> expression induced by salinity was additionally enhanced by Cd treatment. Such changes were not observed for <i>zip4</i>. Stressor-induced alterations in <i>abcc2</i>, <i>cax4</i>, <i>hma4</i> and <i>pcs1</i> expression were most pronounced in the root tissue, and the expression of <i>cax4</i>, <i>hma4</i> and <i>pcs1</i> was upregulated in response to salinity and Cd. However, the cumulative effect of both stressors, similar to the one described for <i>irt2</i>, was observed only in the case of <i>pcs1</i>. The importance of salt stress in the <i>irt2</i> expression regulation mechanism is proposed. To the best of our knowledge, this study is the first to report the combined effect of salinity and heavy metal stress on genes involved in heavy metal trafficking.