Agriculture Reference
In-Depth Information
renamed permease in chloroplast 1 PIC1 (Duy et al.
2007
). The loss-of-function
mutants of PIC1 display chlorotic phenotype and severely impaired growth. More-
over, the mutation causes severe problems in chloroplast development and leads to
disturbed metal homeostasis in leaves.
FRO7, one of the members of the
Arabidopsis
FRO family, localises to the inner
chloroplast membrane and it is thought to be essential for seedling development.
The growth of the fro7 mutant is significantly impaired in alkaline conditions and in
media lacking sugar. Moreover, chloroplasts isolated from the mutant exhibit
significantly lower FRO activity and Fe content compared to the wild type (Jeong
et al.
2008
). These results suggested an important role of FRO7 as a chloroplast Fe
transporter during photosynthesis and development.
In addition, the mitochondria contribute to cellular Fe homeostasis. Indeed a
mutation in the STARIK/ATM3 gene that encodes for a mitochondria ABC trans-
porter leads to chlorosis and reduced growth. The mitochondria of the
starik
mutant
accumulate more non-heme and non-protein bound Fe, as the biosynthesis of Fe-S
clusters in the mitochondria is linked to the intracellular Fe by this transporter
(Kushnir et al.
2001
; Bernard et al.
2009
). A mitochondria iron transporter (MIT)
has been identified in a screening of T-DNA (transfer DNA) of rice in Fe deficiency
conditions (Bashir et al.
2011
). The homozygous knock-out mutant
mit
is lethal,
highlighting the importance of this transporter for plant growth. In contrast, the
heterozygous mutant is viable but severely impaired in growth, exhibiting an
accumulation of Fe in the shoot with less Fe in the mitochondria.
The vacuole also functions to store Fe and avoid toxicity. The vacuolar iron
transporter (VIT) mediates the transport of Fe from the cytosol into the vacuole and
plays a fundamental role in seed and seedling development, as shown by the
analysis of the
vit1
-
1
mutant (Kim et al.
2006
). In contrast, NRAMP3 and
NRAMP4 are influx transporters that function to export Fe from the vacuole into
the cytosol during seed germination (Lanquar et al.
2005
). Their contribution is
essential to provide Fe during development until the seedlings can start to take up
Fe from the environment.
Interaction of Fe and S Metabolism (Uptake, Fe-S Clusters)
Uptake and homeostasis of Fe is known to be linked to other metals such as zinc
(Lin et al.
2009
; Deinlein et al.
2012
). More recently the connection between Fe and
sulfur (S) metabolism is being recognised, mainly because Fe is required together
with S for the biosynthesis of the Fe-S clusters.
The thylakoids in chloroplasts harbour ferredoxin, photosystem I (PSI) and
cytochrome b
6
f complex, which belong to the photosynthetic electron transport
chain. In the stroma, other Fe-S proteins are found; among these there are nitrite
reductase and two key enzymes for sulfur metabolism, sulfite reductase and APR.
In mitochondria, major Fe-S proteins are Complex I, II and III of the respiratory
