Iron Concentration in Crops

Plant Part and Growth Stage

Most of the iron in plants is in the Fe(III) form (11). The Fe(II) form is normally below the detection level in plants (31). A high proportion of iron is localized within the chloroplasts of rapidly growing leaves (10). One of the forms in which iron occurs in plastids is as phytoferritin, a protein in which iron occurs as a hydrous Fe(III) oxide phosphate micelle (9), but phytoferritin is also found in the xylem and phloem (32). It also occurs in seeds, where it is an iron source that is degraded during germination (33). However, in general, concentrations of iron in seeds are lower than in the vegetative organs.

A large part of the iron in plants is in the apoplast, particularly the root apoplast. Most of this root apoplastic pool is in the basal roots and older parts of the root system (34). There is also a noticeable apoplastic pool of iron in the shoots.

In the iron hyperaccumulator Japanese blood grass (Imperata cylindrica Raeuschel), iron accumulates in rhizomes and leaves in mineral form, in the rhizomes in particular as jarosite, KFe₃(OH)₆(SO₄)₂, and in the leaves probably as phytoferritin (35). In the rhizome this accumulation is in the epidermis and the xylem, and in the leaves it is in the epidermis.