Chloride transport at plant-soil interface modulates barley Cd tolerance

Aims: Cadmium (Cd) is a toxic metal in soils and its accumulation in plants poses severe problems to agricultural production and human health. Most of research has focused on the Cd toxicity to plants, but reports on Cd co-transport and regulation by the major counter ion Chloride (Cl) is limited. This study aims to understand the mechanisms of the interaction between soil Cl and phytol-toxicity of Cd. Methods: We utilised soil chemical, plant physiological, biophysical, and molecular approaches to test the hypothesis that Cl transport increases the mobility and phytol-toxicity of Cd to barley. Results: Cd-sensitive Gairdner utilised high amount of Cl− from soil for optimal growth and yield in the control, but this also caused higher tissue Cd uptake and significantly affected photosynthesis in treatments of Cd-Cl combinations. Net ion fluxes from the root mature zone in Cd treatments and relative expression of transporter genes exhibited striking difference between two genotypes. Our results also highlighted evidence that Cd sensitivity is related to higher Cl− and Cd2+ uptake and lower capacity to regulate root ion homeostasis and gene expression. Conclusions: We present a new finding that soil Cl− and Cd availability and Cd uptake and its interaction with other ions play a major role in barley Cd tolerance. These findings will guide future breeding for low Cl− uptake genotypes to reduce Cd accumulation for barley grown in Cd contaminated soils and for the economically sound and cleaner production of barley for the global feed, food and brewery industry.