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

Wheat is a major global food crop, and understanding how essential minerals and cadmium (Cd) accumulate in grain is important for improving nutritional quality and food safety. Here, we integrated developmental ionomics with temporal grain transcriptomics to investigate mineral accumulation from vegetative growth to grain filling. Shoot accumulation of Fe, Mn, Cu, Zn, and Cd followed a characteristic slow-fast-slow pattern, with rapid accumulation centred around the jointing stage. Grain loading showed contrasting source dependencies: Cu and Zn were supplied mainly through remobilization from vegetative tissues, whereas Fe, Mn, and Cd relied predominantly on continued root uptake after anthesis. During grain filling, three distinct accumulation patterns were identified: early accumulation of Ca, sustained accumulation of Fe, and mid-phase accumulation of the remaining elements. Organ-level analysis showed that the flag leaf and node I functioned primarily as transfer hubs rather than major direct sources for grain loading. Temporal transcriptomic analysis identified stage-specific gene expression programs consistent with these accumulation dynamics. Together, these findings establish an integrated framework linking whole-plant element dynamics with grain-level transcriptional programs, providing a basis for improving grain mineral nutrition and reducing Cd accumulation.