Examination of the role of iron deficiency response in the accumulation of Cd by rice grown in paddy soil with variable irrigation regimes

Cd uptake has been shown to increase during conditions of Fe deficiency. This study tested the hypothesis that Fe-deficiency-responsive genes, particularly OsNRAMP1, play a role in the increased Cd uptake that occurs when rice is grown in aerobic soil conditions. Plants were grown in aerobic or flooded soil conditions. Uptake of Cd was compared to levels of expression of candidate metal transporters and to metal ion availability in soil. Plants grown with intermittent soil flooding experienced a predominantly aerobic root environment and had the highest plant Cd uptake. Stronger upregulation of OsNRAMP1 was detected in plants grown in unflooded soil than in flooded soil. However, these transcriptional responses were not linked to an increase in Cd uptake. Overexpression of OsNRAMP1 was not found to increase the uptake of Cd in rice in soil or solution culture. In contrast, there were large differences in availability of Cd, Fe and Mn between flooded and aerobic soils, which were linked to changes in Cd uptake. Aerobic soil conditions favour Cd uptake through increased Cd availability and decreased competition between Cd and Fe rather than through the increased expression of the Fe transporters themselves.