What question did this study set out to answer?

This research aims to understand how nitrate and ammonium affect copper toxicity in Malus plants.

April 25, 2026

Nitrate Has Stronger Copper Detoxification Ability by Reducing Copper Translocation, Enhancing Cell Wall Immobilization, and Modulating Transcriptional Regulation in Malus Rootstock

Key Points

This research aims to understand how nitrate and ammonium affect copper toxicity in Malus plants.
Analyzed copper concentrations and translocation in Malus roots and leaves under copper exposure using different nitrogen forms.
Conducted RNA sequencing to assess gene regulation related to copper uptake and detoxification.
Utilized weighted gene coexpression network analysis to identify key regulatory genes.
Nitrate reduced root and leaf Cu concentrations while enhancing Cu immobilization in cell walls (elevated pectin and hemicellulose levels).
Nitrate decreased reactive oxygen species, enhancing antioxidant levels contrasted with ammonium's promotion of Cu mobility.
RNA sequencing indicated upregulation of cell wall metabolism genes by nitrate, highlighting distinct regulatory pathways from ammonium.

Abstract

An appropriate nitrogen (N) supply alleviates copper (Cu) toxicity, but the underlying mechanisms of different N forms remain unclear. This study investigated the regulatory mechanisms of nitrate (NO3--N) and ammonium (NH4+-N) on Cu uptake, translocation, and tolerance in Malus plants under Cu exposure conditions. Under excess Cu, NO3--N reduced root and leaf Cu concentrations and root-to-shoot translocation but increased Cu sequestration in root cell walls, accompanied by elevated pectin, hemicellulose (HC1 and HC2) contents, and pectin methylesterase (PME) activity, and decreased polygalacturonase activity relative to NH4+-N. In contrast, NH4+-N increased water-soluble Cu, bioconcentration/translocation factors and subcellular Cu in sensitive fractions, indicating enhanced Cu mobility and phytotoxicity. NO3--N lowered reactive oxygen species (ROS) and enhanced nonenzymatic and enzymatic antioxidants. RNA sequencing showed that NO3--N upregulated cell wall metabolism genes, whereas NH4+-N activated Cu uptake/transport genes. Weighted gene coexpression network analysis identified WRKY51 with HUB genes EXPA and BXL. These findings establish physiological and molecular foundations for NO3--N-mediated Cu stress mitigation.

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