Elemental localization in inflorescences of the hyperaccumulators Noccaea praecox and Noccaea caerulescens (Brassicaceae)

Noccaea praecox and Noccaea caerulescens (Brassicaceae) are nickel and zinc hyperaccumulators, native to Europe. To date, most studies have focused on metal accumulation in the leaves, whereas the distribution of metals in the inflorescences of hyperaccumulator plants remains largely unexplored, but of great interest in the context of adaptation to fertility and (insect) pollination. Samples of N. praecox from an ultramafic site and N. caerulescens from an industrially contaminated site were used for synchrotron-based micro-X-ray fluorescence (μXRF) analysis. The results showed that nickel and zinc in the flowers of N. praecox are mainly distributed in the receptacle, ovary, and anthers, but at different concentrations. Similar results were found in N. caerulescens, with the greatest accumulation in the receptacle and ovary, especially in the walls, however at lower levels in the anthers. Although the leaves of N. praecox and N. caerulescens are the main deposition sites for nickel and zinc, significant concentrations of these elements were deposited in the flowers, especially in the pistils and anthers, indicating possible negative effects on fertility and pollinator species.