Nanostructured hydroxyapatite-zinc complex as a novel foliar system to reduce cadmium accumulation in wheat grain: Performance and mechanism

Foliar zinc (Zn) application offers a promising strategy for cadmium (Cd) mitigation and Zn biofortification in wheat, while the poor leaf adhesion of conventional Zn formulations limits their effectiveness. This study utilized hydroxyapatite nanoparticles (nHAP) as a nanocarrier and prepared the nHAP-Zn complex through simple reactions. The complex exhibited superior leaf adhesion compared to ZnSO 4 solution. Foliar application of nHAP-Zn increased grain Zn concentration by 38.8 % in the low-Cd-accumulating wheat cultivar Ningmai-11 (NM11) and 31.6 % in the high-Cd-accumulating cultivar Zhengmai-10 (ZM10), surpassing the effects of ZnSO 4 . Notably, nHAP-Zn decreased grain Cd concentration by 31.5 % in NM11 and 32.9 % in ZM10. Mechanistically, nHAP-Zn suppressed Cd uptake by downregulating the expression of TaNramp5 , TaIRT1 , and TaZIP5 genes in the roots, and inhibited Cd translocation from node I to the grain by reducing xylem-to-phloem Cd transfer-related gene expression (i.e., TaHMA2 , TaZIP3 , and TaZIP7 in NM11, and TaHMA2 , TaLCT1 , TaZIP5 , and TaZIP7 in ZM10). Furthermore, nHAP-Zn application did not compromise plant growth characteristics such as plant biomass and height. These findings highlight nHAP-Zn as a highly efficient foliar fertilizer for enhancing Zn biofortification while mitigating Cd accumulation in wheat cultivated in Cd-contaminated regions. This study presents a novel approach to improving wheat safety and nutritional quality. • Novel nHAP-Zn foliar fertilizer enhances leaf adhesion. • nHAP-Zn was more effective in Zn biofortification and Cd mitigation than ZnSO 4 . • nHAP-Zn reduced Cd uptake by downregulating Nramp5 , IRT1 , and ZIP5 genes in roots. • nHAP-Zn inhibited node I-to-grain Cd translocation via downregulating xylem-phloem transfer genes. • Cd transporter genes in node I exhibit cultivar-specific expression patterns.