Uptake kinetics and translocation of selenite and selenate as affected by iron plaque on root surfaces of rice seedlings.

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CONCLUSION: Iron plaque on root surfaces greatly influenced selenium uptake and played different roles in selenite and selenate uptake. Iron plaque commonly forms on rice root surfaces under flooded conditions, but little is known about the relationship between iron plaque and selenium (Se) accumulation. Here, we investigate the effects of iron plaque on Se uptake by and translocation within rice (Oryza sativa) seedlings, and the kinetics of selenite and selenate influx into rice roots (with or without iron plaque) were determined in short-term (30 min) experiments. Rice seedlings were planted in nutrient solutions containing different levels of ferrous ion for 3 days and then transplanted into nutrient solutions with selenite or selenate. Se concentrations in iron plaque were positively associated with the amounts of iron plaque in both selenite and selenate treatments and iron plaque had a higher affinity for selenite than selenate. Results showed that iron plaque on root surfaces greatly influenced Se uptake and played different roles in selenite and selenate uptake. The selenite and selenate uptake kinetics results demonstrated that the presence of iron plaque enhanced selenite uptake, but decreased selenate uptake. In addition, root-Se concentrations increased with the increasing amounts of iron plaque, but Se translocation from roots to shoots was reduced with the increasing amounts of iron plaque in the +selenite treatment. Iron plaque significantly influenced selenite uptake and might act as a pool to selenite accumulation in rice plants. However, iron plaque had no significant effect on selenate uptake or even as a barrier to selenate uptake.