Agriculture Reference
In-Depth Information
seed Fe concentrations, which suggests that the increase of Fe uptake alone is
not enough. This is logical since Fe moves to leaves via xylem but to seeds it
moves mainly via phloem, as xylem flow is driven by transpiration and seeds
almost do no transpire. A second strategy is to “pull” Fe into the plant by
increasing the sink strength: i.e., by overexpressing Fe storage ferritin genes
[68]. A third strategy is to increase Fe mobilization within the plant: i.e., by
increasing transporters or substrates of transporters, like
YSL
genes (involved
in NA-Fe transport) or
NAS
genes (involved in NA synthesis) [2,65,68]. Most
frequently, Fe researchers use a combination of several of these strategies to
obtain seeds with higher Fe content [65,68].
The obtention of seeds with high Fe content is not enough for human
nutrition: Fe in seeds should be bioavailable. For this, it is important the nature
of the Fe compounds in seeds, the location of Fe within the seed and the
presence of substances that negatively interact with Fe bioavailability, like
phytic acid [65]. The location of Fe within the seeds is important in some plant
species, such as rice, where Fe accumulates in external tissues discarded
during processing and Fe content is very low in the endosperm [2]. In pea
seeds, Fe is accumulated in the epidermis of embryos [2]. Some approaches
used to increase Fe bioavailability in seeds are the use of endosperm-specific
promoters to locate Fe in rice endosperm and the use of phytase genes to
diminish phytic acid in seeds [2,65].
In relation to the Fe biofortification of pea, to our knowledge none of the
strategies mentioned in the previous paragraphs have been applied to this plant
species yet. Nonetheless, there are studies related to this topic, most of them
carried out with the
brz
and
dgl
mutants, that could be very useful for pea Fe
biofortification in the future. As previously mentioned (see Use of mutants…),
both mutants present constitutive activation of Fe responses and, as consequence,
both hyperaccumulate Fe in leaves. For comparison, while the wt pea „Sparkle‟
and „DGV‟ accumulate Fe around 100 g/g DW in leaves,
brz
and
dgl
can
accumulate 5000 to 10000 g/g DW [6,20]. Since both genes function in a
semi-dominant manner, F
1
hybrids exhibit intermediate leaf Fe concentrations
[6,20]. Despite the
brz
mutant accumulates high levels of Fe in leaves, no
increase was measured in the Fe concentration of seeds [6], with suggests that
the remobilization from leaves to seeds through the phloem is similar to the
wt. In supporting this view, both
brz
and its wt parent (cv „Sparkle‟), when
grown with sufficient or excess Fe, exhibit seed Fe concentrations of 70 to 80
g/g DW [6]. However, for the
dgl
mutant the results are different. When
grown with sufficient or excess Fe, Fe concentration in
dgl
seeds was 250 g/g
DW, 3.5-fold that of wt seeds [6]. These results suggest that the
dgl
mutation
