Localized nitrate uptake by NRT1.8 antagonizes root meristem growth inhibition upon cadmium stress

Heavy metal pollution and overuse of nitrogen fertilizer have essentially deteriorated soil environments, though how these two factors interact with each other to impact plant growth remains largely unknown. Here, we reported polar localization of NRT1.8 towards the soil side at epidermal cells adjacent to lateral root caps (LRC). The combined treatment of Cd and high nitrate induced NRT1.8 expression at root tips, leading to uptake of more NO₃^- from LRC into inner cells, meanwhile, unloading of NO₃^- from the xylem to collaboratively maintain NO₃^- level in the root tip. The root length and meristematic cell numbers are significantly decreased in the nrt1.8 mutant compared to the wild-type when exposed to the combined treatment. Further investigation found that the NRT1.8-mediated nitrate uptake in the root tip leads to nitric oxide (NO) accumulation, which functions to alleviate root growth inhibition upon Cd stress, and promotes cell proliferation of the meristematic zone. Our research identified the LRC region as an important site for the entry of nitrate under stress conditions and for maintaining nitrogen levels in this area, providing a good model to understand cell-to-cell communication during root response to complex soil deterioration.