Iron in leaves: chemical forms, signalling, and in-cell distribution

Following iron transport to leaves, proper control over its location and incorporation is required, while sensing of the organellar iron status is also crucial. Iron (Fe) is an essential transition metal. Based on its redox-active nature under biological conditions, various Fe compounds serve as cofactors in redox enzymes. In plants, the photosynthetic machinery has the highest demand for Fe. In consequence, the delivery and incorporation of Fe into cofactors of the photosynthetic apparatus is the focus of Fe metabolism in leaves. Disturbance of foliar Fe homeostasis leads to impaired biosynthesis of chlorophylls and composition of the photosynthetic machinery. Nevertheless, mitochondrial function also has a significant demand for Fe. The proper incorporation of Fe into proteins and cofactors as well as a balanced intracellular Fe status in leaf cells require the ability to sense Fe, but may also rely on indirect signals that report on the physiological processes connected to Fe homeostasis. Although multiple pieces of information have been gained on Fe signalling in roots, the regulation of Fe status in leaves has not yet been clarified in detail. In this review, we give an overview on current knowledge of foliar Fe homeostasis, from the chemical forms to the allocation and sensing of Fe in leaves.

Automated summary

Proper control and sensing of iron incorporation is crucial for maintaining foliar iron homeostasis, especially for the synthesis of chlorophylls and stability of the photosynthetic machinery in leaves. While the signaling of iron in roots has been extensively studied, the regulation of iron status in leaves remains to be further clarified.