Characterization of Differential Cesium Toxicity and Cesium-affected Transcription of K⁺ or Na⁺ Transporter Genes in Model Plants and Horticultural Crops

Pollutant toxicity influences biomass increment and pollutant uptake in phytoremediation; therefore, tolerance to pollutant toxicity is important in determining applicability of candidate plants. This study investigated relative Cs toxicity in Arabidopsis, cabbage, lettuce, red pepper, rice, and tomato seedlings through growth, photosynthesis, and/or transcription assays. When treated with 100, 300, 800, or 1,500 μM CsCl, the six plant species showed substantial differences in changes in seedling weight, chlorophyll content, photosynthetic activity, or transcription of K⁺or Na⁺transporter genes, and exhibited higher susceptibility to Cs toxicity in the order of Arabidopsis+ or Na⁺ transporter genes, NHX5, SOS1, KT1, NHD1, and HKT1, a high-affinity potassium transporter gene HKT1 and a sodium hydrogen antiporter gene NHD1 showed Cs concentration-dependent decrease in transcription, associating more with Cs toxicity than Cs uptake. In contrast, a low-dose gamma radiation of 8 Gy increased shoot growth slightly but decreased Cs uptake in seedlings. Taken together, these results suggest that the differential Cs toxicity to these six plant species could be somewhat associated with the distinctive transcription of K⁺ or Na⁺ transporter genes and that salt or osmotic stress and gamma radiation could indirectly modulate Cs toxicity or Cs uptake