The pH strongly influences the uranium-induced effects on the photosynthetic apparatus of Arabidopsis thaliana plants

To study the impact of environmental uranium contamination, effects should be analysed at different environmentally relevant pH levels as the speciation of U is strongly dependent on the pH. As photosynthesis is a major energy producing process in plants, the effects of different U concentrations on photosynthesis in 18-day-old Arabidopsis thaliana are investigated at pH 4.5 and pH 7.5. At pH 4.5, U is highly taken up by the roots but is poorly translocated to the shoots, while at pH 7.5, less U is taken up but the translocation is higher.U does not influence the photosynthetic machinery at pH 7.5, while an optimization of the photosynthesis takes place after U exposure at pH 4.5. As such, more of the absorbed quanta are effectively used for photosynthesis accompanied by a decreased non-photochemical quenching and an increased electron tranposrt rate. Since the enhanced photosynthesis at pH 4.5 is accompanied by a decreased growth, we suggest that the energy produced during photosynthesis is used for defence reactions against U-induced oxidtaive stress rather than for growth. As such, a high discrepancy was observed between the two pH levels, with an optimized photosynthetic apparatus at pH 4.5 and almost no effects at pH 7.5.