Polymer‐Coated Manganese Dioxide Nanoparticles for Foliar Mn Delivery: Mechanisms of Uptake and Metabolic Responses in Mn Deficient Barley

Andrea PinnaUniversity of Copenhagen

Asbjørn Krarup GrønbækUniversity of Copenhagen

Emil Visby KristensenTechnical University of Denmark

Noémie ThiébautUniversity of Copenhagen

Augusta SzameitatUniversity of Copenhagen

Birte Martin‐BertelsenUniversity of Copenhagen

Tue HassenkamUniversity of Copenhagen

Jean‐Claude GrivelTechnical University of Denmark

Rajmund MoksoTechnical University of Denmark

Søren HustedUniversity of Copenhagen

Small·February 4, 2026

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Abstract

Efficient foliar delivery of manganese (Mn) remains a major challenge in crop nutrition due to the low phloem mobility of Mn 2 + ions and the risk of leaf scorching from conventional Mn salts. This study investigates the uptake and assimilation of foliar‐applied ∼25 nm polyacrylic acid‐coated manganese dioxide nanoparticles (nPAA‐MnO 2 ) in 4‐week‐old Mn‐deficient barley ( Hordeum vulgare ) and compares them to ionic Mn. Complementary imaging methods showed rapid (2 h) leaf penetration of nPAA‐MnO 2 through stomata, facilitated by the formulation´s low surface tension and the addition of 3% glycerol as a humectant. Although ionic Mn displayed higher uptake efficiency than nPAA MnO 2 (∼90% vs ∼11%), the latter restored Mn‐dependent photosynthetic functionality without inducing phytotoxicity, even at high Mn concentrations (4 g L −1 ). Labeling experiments with tracer ions revealed nPAA‐MnO 2 hotspots around vascular bundles and a small (1.9%), yet significant, basipetal translocation of Mn out of the foliar application zone after 4 days, compared to only 0.1% for ionic Mn. By delineating the distinct uptake pathways and metabolic fate of nPAA‐MnO 2 versus ionic Mn, these findings provide the mechanistic foundation for developing a novel generation of nano‐enabled strategies to address Mn and other micronutrient deficiencies in crops.

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