Nitrate transporter 1.1 alleviates lead toxicity in Arabidopsis by preventing rhizosphere acidification

Abstract

Exposure to Pb ²⁺ increases NRT1.1-mediated uptake of nitrate in Arabidopsis and is associated with decreased uptake of Pb into the plant, which is a consequence of decreased acidification in the rhizosphere.

Abstract

Identification of the mechanisms that control lead (Pb) concentration in plants is a prerequisite for minimizing dietary uptake of Pb from contaminated crops. This study examines how nitrate uptake by roots affects Pb uptake and reveals a new resistance strategy for plants to cope with Pb contamination. We investigated the interaction between nitrate transporter (NRT)-mediated NO ₃ ^– uptake and exposure to Pb in Arabidopsis using NRT-related mutants. Exposure to Pb specifically stimulated NRT1.1-mediated nitrate uptake. Loss of function of NRT1.1 in nrt1.1-knockout mutants resulted in greater Pb toxicity and higher Pb accumulation in nitrate-sufficient growth medium, whereas no difference was seen between wild-type plants and null-mutants for NRT1.2, NRT2.1, NRT2.2, NRT2.4, and NRT2.5. These results indicate that only NRT1.1-mediated NO ₃ ⁻ uptake alleviated Pb toxicity in the plants. Further examination indicated that rhizosphere acidification, which favors Pb entry to roots by increasing its availability, is prevented when NRT1.1 is functional and both NO ₃ ^– and NH ₄ ⁺ are present in the medium.