Cadmium-induced iron deficiency is a compromise strategy to reduce Cd uptake in rice

Abstract

Expose of cadmium (Cd) leads to severe leaf chlorosis and reducing nutrient uptake. It is unclear how plants responded to Cd stress in the roots, and its relation to the leaf chlorosis. Our results showed Cd disturbed the homeostasis of multiple nutrient element at different levels. The most reduced elements were Mn, Fe, with 96 %, 89 % decline in the leaves, that caused leaf chlorosis. The plants actively downregulated the expression of metal transporters to reduce Cd uptake, but consequently reducing Fe and Mn uptake. Moreover, Cd stress promoted the formation of iron plaque and significantly reduced the exchangeable ions on root surface. Importantly, ethylene plays an essential role in regulating iron plaque formation and the existent forms of Cd. Blocking ethylene biosynthesis significantly increased exchangeable Cd on the root surface and decreased the percentage of iron oxides bound Cd, thus leading to increase of Cd in the shoots. Above all, our results revealed plants actively control the expression of metal transporter and the ethylene-dependent iron plaque formation to reduce Cd uptake, but sacrificed iron nutrition. The mechanism of sequester Cd on rhizosphere by ethylene in response to Cd stress may provide guidelines for the mitigation of Cd accumulation in rice via ethylene-dependent rhizosphere regulation.