Plant Molecular Biology 50: 587–597, 2002.
© 2002 Kluwer Academic Publishers. Printed in the Netherlands.
Knock-out of Arabidopsis metal transporter gene IRT1 results in iron
deﬁciency accompanied by cell differentiation defects
, Markus Klein
, Enrico Martinoia
, Urs Feller
, Jeff Schell
Maria S. Pais
and Csaba Koncz
ICAT, Campus da Faculdade de Ciências da Universidade de Lisboa, 1749-016 Lisboa, Portugal;
Plant Physiology, Comenius University, Mlynska dolina B2, 84 215 Bratislava, Slovakia;
Institut de Botanique, Laboratoire de Physiologie V´eg´etale, Rue Emile Argand 13, CH-2007 Neuchâtel, Switzer-
University of Bern, Institute of Plant Sciences, Alterbergrain 21, CH-3013 Bern, Switzerland;
Institut für Züchtungsforschung, Carl-von-Linn´e-Weg 10, 50829 Köln, Germany (
author for correspondence,
Received 28 December 2001; accepted in revised form 25 February 2002
Key words: Arabidopsis, insertion mutagenesis, IRT, metal-transporter, ZIP
IRT1 and IRT2 are members of the Arabidopsis ZIP metal transporter family that are speciﬁcally induced by
iron deprivation in roots and act as heterologous suppressors of yeast mutations inhibiting iron and zinc uptake.
Although IRT1 and IRT2 are thought to perform redundant functions as root-speciﬁc metal transporters, insertional
inactivation of the IRT1 gene alone results in typical symptoms of iron deﬁciency causing severe leaf chlorosis and
lethality in soil. The irt1 mutation is characterized by speciﬁc developmental defects, including a drastic reduction
of chloroplast thylakoid stacking into grana and lack of palisade parenchyma differentiation in leaves, reduced
number of vascular bundles in stems, and irregular patterns of enlarged endodermal and cortex cells in roots. Pulse
Fe through the root system shows that the irt1 mutation reduces iron accumulation in the shoots.
Short-term labeling with
Zn reveals no alteration in spatial distribution of zinc, but indicates a lower level of
zinc accumulation. In comparison to wild-type, the irt1 mutant responds to iron and zinc deprivation by altered
expression of certain zinc and iron transporter genes, which results in the activation of ZIP1 in shoots, reduction of
ZIP2 transcript levels in roots, and enhanced expression of IRT2 in roots. These data support the conclusion that
IRT1 is an essential metal transporter required for proper development and regulation of iron and zinc homeostasis
Abbreviations: IRT, Iron-Regulated Transporter, ZRT, Zinc-Regulated Transporter, ZIP, ZRT, IRT-like Protein
Iron limitation is a common form of environmental
stress that affects agricultural production worldwide.
In many soil types iron is predominantly available as
insoluble ferric oxide/hydroxide, which is not read-
ily accessible for uptake by plants. Although a large
amount of iron is stored in complex with ferritin within
the chloroplasts, this bound iron cannot be mobilized
from mature to young leaves (Waldo et al., 1995).
Therefore, young leaves become chlorotic during iron
limitation due to inhibition of chloroplast biogenesis
and chlorophyll biosynthesis. The ﬁrst signs of leaf
chlorosis coincide with morphological alterations in
the roots, where root hair formation increases along
with thickening of the root cortex (Landsberg, 1994,
1996). In some plant species, but not in Arabidop-
sis, rhizodermal cells differentiate to so-called transfer
cells providing a large plasma-membrane surface for
enhanced mineral nutrient absorption (Schmidt and
Bartels, 1996; Schmidt et al., 2000).