Research Article

Plant and Soil

, Volume 284, Issue 1, pp 101-108

First online:

Expression, localization, and regulation of the iron transporter LeIRT1 in tomato roots

  • A. SchikoraAffiliated withBiochimie et Physiologie Moléculaire des Plantes, INRA
  • , O. ThimmAffiliated withMetanomics GmbH
  • , B. LinkeAffiliated withInstitute of Biology, Humboldt-University Berlin
  • , T. J. BuckhoutAffiliated withInstitute of Biology, Humboldt-University Berlin
  • , M. MüllerAffiliated withInstitute of Biology, Humboldt-University Berlin
  • , W. SchmidtAffiliated withInstitute of Plant and Microbial Biology, Academia Sinica Email author 

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Abstract

Iron deficiency induces an array of developmental, metabolic and physiological responses that aid in improved acquisition of iron. As part of these responses, some root epidermal cells of so-called strategy I species develop conspicuous ingrowths at the outer tangential walls typical of transfer cells. These cells, characterized by a high area/volume ratio and numerous mitochondria, are thought to support the uptake of iron from the rhizosphere into the root symplasm by preferentially harboring proteins involved in iron acquisition. In the present study, we have analyzed the expression of the iron-regulated transporters LeIRT1 and LeIRT2 at the transcriptional level and show that LeIRT1 but not LeIRT2 is up-regulated in both roots and shoots in tomato (Lycopersicon esculentum Mill.) upon iron deficiency. Split-root studies reveal that expression of LeIRT1 is higher in roots that have been grown in the presence of iron then in roots grown in the absence of iron. In contrast, the frequency of transfer cells is higher in iron-deficient split roots. Protein abundance of LeIRT1 followed the same pattern; although, the difference in LeIRT1 between the split-root halves is less pronounced than those of the transcripts. Immunocytochemical analysis showed that LeIRT1 protein is polarized to membranes of distal tangential walls of epidermal cells. Protein density is not markedly higher in transfer cells compared to normal rhizodermal cells, suggesting a non-specific support of iron uptake by transfer cells via an increase in the surface/volume ratio. The results further indicate separate regulatory pathways for developmental and physiological responses to iron deficiency.

Keywords

Immunochemistry Iron uptake Real-time PCR Split-roots Transfer