Iron uptake system mediates nitrate-facilitated cadmium accumulation in tomato ( Solanum lycopersicum) plants

Abstract

Nitrogen (N) management is a promising agronomic strategy to minimize cadmium (Cd) contamination in crops. However, it is unclear how N affects Cd uptake by plants. Wild-type and iron uptake-inefficient tomato ( Solanum lycopersicum) mutant (T3238 fer) plants were grown in pH-buffered hydroponic culture to investigate the direct effect of N-form on Cd uptake. Wild-type plants fed NO ₃ ⁻ accumulated more Cd than plants fed NH ₄ ⁺. Iron uptake and LeIRT1 expression in roots were also greater in plants fed NO ₃ ⁻. However, in mutant T3238 fer which loses FER function, LeIRT1 expression in roots was almost completely terminated, and the difference between NO ₃ ⁻ and NH ₄ ⁺ treatments vanished. As a result, the N-form had no effect on Cd uptake in this mutant. Furthermore, suppression of LeIRT1 expression by NO synthesis inhibition with either tungstate or L-NAME, also substantially inhibited Cd uptake in roots, and the difference between N-form treatments was diminished. Considering all of these findings, it was concluded that the up-regulation of the Fe uptake system was responsible for NO ₃ ⁻ -facilitated Cd accumulation in plants.