Decoding plant responses to iron deficiency

Abstract

Plants respond to iron deprivation by inducing a series of physiological and morphological responses to counteract the nutrient deficiency. These responses include: (i) the acidification of the extracellular medium, (ii) the reduction of ferric ion and (iii) the increased transport of ferrous ion inside of root cells. This iron transport system is present in strategy I plants and is strictly regulated; at low iron concentration the responses are induced whereas upon iron supply they are repressed. The mechanisms related with this process has been extensively studied, however, the specific cellular effectors involved in sensing iron deficiency, the cascade of components participating in signal transduction, and the way iron is metabolized and delivered, are yet poorly understood. Recently, it has been proposed nitric oxide (NO) as a signaling molecule required for plant responses to iron deficiency. NO is produced rapidly in the root epidermis of tomato plants that are growing under iron deficient conditions. Furthermore, it was demonstrated that NO is required for the expression and activity of iron uptake components in roots during iron deprivation. Here we propose and discuss a working hypothesis to understand the way NO is acting in plants responses to iron deficiency. We specifically highlight the cross talk between NO and plant hormones, and the interaction between NO, iron and glutathione for the formation of dinitrosyl iron complexes (DNICs). Finally, a potential role of DNICs in iron mobilization is proposed.

Addendum to: Graziano M, Lamattina L. Nitric oxide accumulation is required for molecular and physiological responses to iron deficiency in tomato roots. Plant J 2007; 52:949-60.

Acknowledgments

This work was supported by Agencia Nacional de Promoción Científica y Tecnológica (ANPCyT, PICTs 38078/05, and 1-14457/03 to L.L.), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET, PIP 0898/98 to L.L.) and institutional grants from Universidad Nacional de Mar del Plata (UNMdP), Argentina. L.L. is a member of the research staff, L.R. is a postgraduate fellow and M.G. is a Ph.D. student from CONICET, Argentina.

Figures and Tables

Figure 1 Schematic illustration of a model proposing a role for NO, hormones and DNICs during iron deprivation in strategy I plants. Iron deficiency can activate different pathways, probably via the interrelation between NO and hormones (auxin and/or ethylene). NO production is increased during low iron supply in tomato roots. Increased accumulation of FRO1 and IRT1 transcripts results from an NO mediated enhanced FER expression. In this context, iron uptake system in root cells would be activated. In addition, GSH production induced by iron deprivation together with free or protein associated iron in presence of high NO concentration would induce the formation of DNICs in roots cells. These complexes could be a mechanism of iron transport and delivery to others plant cells or organs improving the bioavailability of iron levels.

Addendum to: