Iron availability affects the function of mitochondria in Fe-deficient cucumber roots

• In Strategy-I-plants, iron (Fe) deficiency induces processes leading to increased Fe solubilization in the rhizosphere, including reduction by ferric reductases and active proton extrusion. These processes require active respiration to function. In this work we investigated the effect of Fe deficiency on respiratory activities of cucumber (Cucumis sativus) roots. • We compared oxygen consumption rate and the activities of the respiratory chain complexes on purified mitochondria from roots grown in the presence or absence of Fe using biochemical and molecular approaches. • Oxygen consumption rate in apex roots was increased under Fe deficiency that was mostly resistant to KCN and salycilichydroxamic acid (SHAM) inhibitors, indicating other oxygen-consuming reactions could be present. Indeed, enzyme assays revealed that lack of Fe induced a decrease in the activities of respiratory complexes that was proportional to the number of Fe atoms in each complex. A decrease of cyt c, Rieske and NAD9 proteins was also observed. Transmission electron microscopy (TEM) analysis showed that mitochondria undergo structural changes under Fe deficiency. • Our data show that mitochondria and the electron transport chain are an important target of Fe limitation and that mitochondria modify their function to meet higher demands for organic acids while restricting the activity of enzymes with Fe cofactors.