Excessive iron accumulation in the pea mutants dgl and brz: subcellular localization of iron and ferritin

The pea (Pisum sativum L.) mutants dgl and defective in the regulation of i ron uptake. Enhanced proton extrusion and constitutively high Fe(III) reduc tase activities in the roots lead to an accumulation of iron and other diva lent cations in different organs of the mutants. Ultrastructural investigat ions of the basal leaflets of the mutants revealed in the cytoplasm, in mit ochondria and especially in, or close to the endoplasmic reticulum numerous electron-dense particles which were absent in the corresponding wild type plants DGV and Sparkle. By means of electron-spectroscopic imaging and elec tron-energy-loss spectroscopy it could be shown that these electron-dense p articles consist mainly of iron. Some of the iron deposits were immunocytoc hemically identified as the iron-storage protein ferritin. It is suggested that the precipitation of excessive iron in the dgl and brz mutant leaves i n the form of electron-dense iron particles combined with the accumulation of ferritin is part of the plant defense mechanism against Fe-mediated oxid ative stress.