Project summary

Radiocaesium (¹³⁷Cs) has contaminated agricultural land. It is harmful and enters the food chain through plants. This poses a serious health risk to humans and animals consuming contaminated produce.  It may be possible to develop plant-based strategies to minimise the entry of Cs to the food chain. For example, 'safe' crops containing less Cs in their edible portions could be cultivated on contaminated land. Using a model cruciferous plant species, Arabidopsis thaliana, we are elucidating the molecular mechanisms impacting on shoot Cs concentration. The information provided by this approach could be used to determine the feasibility and guide the selection or breeding of 'safe' crops.

Caesium (Cs) is taken up across the plasma membrane of root cells through K transporters. Initial investigations revealed that intracellular competition of Cs for K-binding sites on essential proteins is the mechanism of Cs toxicity in plants. To determine which transporters mediate Cs entry, Arabidopsis mutants lacking specific K transporters were generated and their accumulation of Cs compared to wildtype plants. Several mutants lacking CNGCs, (non-selective cyclic-nucleotide gated cation channels) had significantly different shoot Cs concentrations and tolerance to both external and internal Cs, when compared to wildtype. Cs fluxes in the xylem and phloem of wildtype plants and mutants with altered shoot Cs concentrations differed. Transcriptional profiling revealed that the complement of Cs-transporting proteins changed with external ionic conditions, and that in K-deficient plants Cs is likely to be transported by high affinity K transporters (KUPs). Thus, although breeding for varied CNGC and/or KUP activity could restrict Cs uptake and enable 'safe' crops to be grown on contaminated land, whole plant responses of plants to the mineral environment should be considered when selecting crops for a particular purpose.

References

Hampton CR, Bowen HC, Broadley MR, Hammond JP, Mead A, Payne KA, Pritchard J, White PJ 2004. Cesium toxicity in Arabidopsis. Plant Physiology 136: 3824-3837

Payne KA, Bowen HC, Hammond JP, Hampton CR, Lynn JR, Mead A, Swarup K, Bennett MJ, White PJ, Broadley MR. 2004. Natural genetic variation in caesium (Cs) accumulation by Arabidopsis thaliana. New Phytologist 162: 535-548

White PJ, Broadley MR. 2000. Mechanisms of caesium uptake by plants. New Phytologist 147: 241-256

White PJ, Swarup K, Escobar-Gutiérrez AJ, Willey NJ, Broadley MR. 2003.  Selecting plants to minimise radiocaesium in the food chain.  Plant & Soil 249: 177-186