Cell Biology of Chromerids: Autotrophic Relatives to Apicomplexan Parasites - International Review of Cell and Molecular Biology - page 354

6.2. Other metabolic features of C. velia

Two main strategies are usually used to uptake iron by terrestrial microor-
ganisms and plants. By way of reductive uptake mechanism, the extracellular
ferric complexes are, via transplasma membrane electron transfer, dissociated
by reduction. Afterward, the high-affinity permease system together with
copper-dependent oxidase will import free iron. The alternative mechanism
uses specific copper-independent receptors that take up siderophores with-
out prior dissociation. In contrast to both canonical mechanisms, C. velia
uptakes iron in a novel manner ( Sutak et al., 2010 ). It was shown that its
transplasma membrane electron transfer system is absent and therefore extra-
cellular ferric chelates cannot be reduced. Hydroxymate siderophores also
cannot be used by this alga as a source of iron. A ferrous chelator does
not inhibit an uptake from ferric citrate, but a higher concentration of ferric
ligand strongly reduces the iron uptake. Moreover, it was demonstrated that
the cell wall of C. velia contains many receptors of iron, which is concen-
trated in close proximity of the transport sites. It seems that aqueous ferric
ions are first concentrated in the cell wall and subsequently taken up without
prior reduction ( Sutak et al., 2010 ).
The most abundant category of lipids associated with the plant and algal
plastidial membranes is represented by galactolipids. Their fraction can reach
up to 85% of all lipids in these cells ( Jouhet et al., 2007 ). Galactolipids such as
monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol
(DGDG) are otherwise found exclusively in cyanobacteria, the predecessors
of plastids. These compounds are in phototrophic eukaryotes synthesized by
galactosyltransferases located in the plastidial membranes ( Bott´ et al., 2011;
Jouhet et al., 2007; Joyard et al., 2010 ). Although no enzyme involved in the
synthesis of galactolipids has been found in the apicomplexan genomes
( Bott´ et al., 2005 ), galactolipid-like compounds displaying similar mobility
as the plant MGDG and DGDG were found in the lysates of T. gondii and
P. falciparum ( Marechal et al., 2002 ). Moreover, a DGDG-like lipid was
detected in total extracts from these coccidians ( Bisanz et al., 2006 ), and
anti-DGDG antibodies were instrumental in the detection of digalactolipids
in the pellicle membrane of T. gondii ( Bott´ et al., 2008 ). When studied in
C. velia , both MGDG-like and DGDG-like galactolipid compounds com-
igrating with spinach galactolipids were found ( Bott ´ et al., 2011 ). In con-
trast to T. gondii , where the DGDG-like molecules were detected outside
the apicoplast ( Bott´ et al., 2008 ), the same galactolipids were located at
multiple membranes of the complex C. velia plastid, which is in good