Tracing nutrient and cadmium accumulation in wheat from vegetative growth to grain filling: source dependencies and...

Wheat is a major global food crop, and the content of essential minerals and toxic elements in the grains is crucial for human nutrition and health. However, their accumulation dynamics across developmental stages and their allocation mechanisms during grain filling remain poorly understood. Here, we systematically investigated the accumulation of essential minerals and toxic elements in field-grown wheat throughout its growth cycle and integrated source contribution analysis with temporal grain transcriptomics during grain filling. Shoot accumulation of Fe, Mn, Cu, Zn, and Cd followed a characteristic slow-fast-slow pattern, peaking at the jointing stage. Element allocation strategies were strongly influenced by phloem mobility: Cu and Zn were primarily remobilized from vegetative organs (>55% contribution), whereas Fe, Mn, and Cd were mainly derived from direct root uptake (>70%). During grain filling, ten elements exhibited three distinct temporal patterns: early accumulation (Ca), mid-phase accumulation (Mg, S, P, K, Mn, Cu, Zn, Cd) synchronized with dry matter, and continuous accumulation (Fe). Organ-level analysis further indicated that the flag leaf and node I acted primarily as transfer and regulatory hubs rather than major direct sources for grain loading. Temporal transcriptomic analysis of developing grains identified early and sustained gene expression patterns corresponding to these phased accumulation dynamics, suggesting stage-specific regulation of element import, redistribution, buffering, and deposition. Together, these results support a two-level interpretation of wheat grain mineral accumulation under the field conditions examined, in which whole-plant source dynamics interact with grain-associated handling processes. This study provides a mechanistically informed insights that may guide future efforts to improve grain mineral nutrition and reduce Cd accumulation through integrated breeding and agronomic strategies.