Agriculture Reference
In-Depth Information
found to mediate the transport of NA-Fe complexes (Curie et al.
2009
). The
Arabidopsis
YSL1 and YSL2 proteins were found to localise to the plasma mem-
brane and to function in yeast complementation assay (Chu et al.
2010
). They are
active in leaves and in flowers and are therefore required for the fertility and the
development of seeds and for the distribution of Fe to the seeds. The two trans-
porters and
AtYSL3
are quite closely related but they have distinct functions in the
plant, as neither
YSL1
nor
YSL2
under control of
YSL3
promoter could complement
the double mutant
ysl1ysl3
. YSL4 and YSL6 were found to localise to the chloro-
plast (Divol et al.
2013
), to the tonoplast and to internal membranes (Chu
et al.
2013
). They are thought to mediate the release of Fe from the chloroplast in
case of Fe overload, thus controlling Fe homeostasis.
NA certainly represents the principal Fe chelator in the cell for different reasons
(reviewed by Hell and Stephan
2003
). It can form complexes with both Fe
3+
and
Fe
2+
at neutral and basic pH, NA-Fe complexes are unlikely to react with oxygen in
the Fenton reaction, NA is found in all plant tissues and also all plant species its
concentration positively correlates with the root areas of Fe uptake. NA is also
involved in loading the seeds with Fe (Klatte et al.
2009
). It is, however, also able to
bind and transport other transition metals such as zinc (Haydon et al.
2012
).
Partitioning of Fe in the Organelles
The partitioning of Fe to the organelles must be tightly regulated, due to the high
requirement for the biosynthesis of Fe-S clusters in both chloroplasts and mito-
chondria. In addition, synthesis of cytosolic Fe-S depends on provision of a
precursor from the mitochondria (Balk and Pilon
2011
). The import of Fe into the
chloroplast also represents an important strategy to store Fe in a non-toxic and
available form. Indeed the largest amount of Fe in plant cells is found in the
chloroplast, where 80-90 % of Fe is accumulated (Marschner
1995
). The members
of the ferritin family (FER) play a fundamental role to prevent oxidative damage in
case of Fe overload. Ferritins are spherical protein complexes formed by 24 sub-
units. They can internalise Fe atoms in their central cavity and can release them
when needed (Briat et al.
2010
). Animal ferritins are regulated mostly at the
translational level, while phytoferritins are mainly subjected to transcriptional
regulation.
In
Arabidopsis
, there are four ferritin isoforms (FER1, FER2, FER3 and FER4).
A loss-of-function approach was used to investigate the role of this protein in
different plant tissues (Ravet et al.
2009
). The analysis showed that plants lacking
ferritins were more sensitive to excess of Fe, with reduced growth and defects in
flower development. Moreover, loss-of-function mutant plants presented differen-
tial regulation of genes related to Fe uptake and higher level of ROS and conse-
quently higher activity of detoxifying enzymes. Electron microscopy has shown
that plant ferritins localise to the plastids, mainly to non-photosynthetic ones such
as proplastids, etioplasts and amyloplasts (Seckback
1982
). The loss-of-function
