Botanical iron minerals: correlation between nanocrystal structure and modes of biological self-assembly

Plants, like animals, use and store iron in their cells. Yet, the compositi on and structure of the plant-iron biominerals, constituting the inorganic cores of phytoferritin, have remained unknown. Transmission electron micros copy (TEM) and diffraction studies of subcellular phytoferritin, extracted from disrupted plant cells, indicate that phytoferritin occurs as crystalli ne magnetite (Fe3O4), epsilon -Fe2O3 and hematite (alpha -Fe2O3), with typi cal sizes of single crystallites in the I - 50 nm range and agglomerate gra in sizes up to 4 mum. The three dimensional agglomerates are built with dif ferent biomineral nanocrystals in three distinct modes of biological self-a ssembly: 1) ordered magnetite; 2) semi-ordered mixture of magnetite and eps ilon -Fe2O3; and 3) random hematite. These self-assemblies correspond to pr ior TEM reports of crystalline, paracrystalline and amorphous phytoferritin arrangements in sectioned cell samples. A fourth plant-iron biomineral, te ntatively assigned as calcium ferrate hexahydrate, has a morphology and dif fraction patterns distinct from the phytoferritin aggregates. We do not att ribute the plant iron observed in this study to be the results of atmospher ic pollution.