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Trace Elements in Abiotic and Biotic Environments
23.5 PLANTS
Iron mobility in soils is the main factor that governs its phytoavailability. Main
features of the Fe uptake by plants, and Fe transport between plant organs may be
summarized as follows:
r Various Fe species are taken up, mainly as Fe 2+ , but also Fe 3+ and Fe
chelates.
r Plant roots may reduce Fe 3+ to Fe 2+ , which is the fundamental process in the
Fe absorption by most plants.
r At Fe deficiency conditions, roots (especially of cereals and other
Gramineae) release mugineic acid, which mobilize Fe species.
r In xylem exudates, Fe occurs mainly in unchelated forms.
r Fe transportation within plants is mediated largely by citrate chelates and
by soluble ferritins (transferins).
r Pine trees, growing in most sites, uptake less Fe by root system than from
aerial deposition.
At conditions of the Fe deficiency, roots of some plants can develop various mechanisms to enhance its availability through the reduction of Fe 3+ , and/or chelation
in phytosiderophore forms, that are efficient in mobilizing Fe (Marschner 2005).
On root surface of some plants grown in waterlogged soils (e.g., rice) is formed Fe
plaque, due to the oxidation of Fe 2+ to Fe 3+ , and the precipitation of Fe oxides on the
root surface. This plaque is composed mainly of ferrihydrite and goethite, and highly
inhibits the Fe uptake (Zhu et al. 2005). Easily available Fe species are its complexes
with some humate forms.
Both Fe uptake and transportation within plant organs are strongly affected by
several soil and plants factors. In general, a high degree of the oxidation of Fe compounds, Fe precipitation on carbonates and/or phosphates, and competition of trace
metal actions with Fe 2+ for the same binding sites of chelating compounds are responsible for a low Fe uptake and for the disturbance of its transport within plant organs.
Iron is considered to be the key metal in the energy transformation needed for
several live processes of plant cells. Its essential roles in the plant metabolism, presented in oversimplified and generalized forms, are as follows:
r Several Fe proteins, mainly transferrins, ferritins, and siderophores, are
involved in transport, storage, and binder systems.
r Fe occurs in heme and nonheme proteins and is concentrated in chloroplasts.
r Fe highly influences the formation of chlorophyll.
r Organic Fe complexes are involved in the electron transfer.
r Fe is directly implicated in the metabolism of nucleic acids.
r Both cations, Fe 2+ and Fe 3+ , play a catalytic role in various metabolic
processes.
Iron deficiency affects several physiological processes, and therefore retards plant
growth and yield. Its deficiency in several crops is now a major worldwide problem.
Trace Elements in Abiotic and Biotic Environments
23.5 PLANTS
Iron mobility in soils is the main factor that governs its phytoavailability. Main
features of the Fe uptake by plants, and Fe transport between plant organs may be
summarized as follows:
r Various Fe species are taken up, mainly as Fe 2+ , but also Fe 3+ and Fe
chelates.
r Plant roots may reduce Fe 3+ to Fe 2+ , which is the fundamental process in the
Fe absorption by most plants.
r At Fe deficiency conditions, roots (especially of cereals and other
Gramineae) release mugineic acid, which mobilize Fe species.
r In xylem exudates, Fe occurs mainly in unchelated forms.
r Fe transportation within plants is mediated largely by citrate chelates and
by soluble ferritins (transferins).
r Pine trees, growing in most sites, uptake less Fe by root system than from
aerial deposition.
At conditions of the Fe deficiency, roots of some plants can develop various mechanisms to enhance its availability through the reduction of Fe 3+ , and/or chelation
in phytosiderophore forms, that are efficient in mobilizing Fe (Marschner 2005).
On root surface of some plants grown in waterlogged soils (e.g., rice) is formed Fe
plaque, due to the oxidation of Fe 2+ to Fe 3+ , and the precipitation of Fe oxides on the
root surface. This plaque is composed mainly of ferrihydrite and goethite, and highly
inhibits the Fe uptake (Zhu et al. 2005). Easily available Fe species are its complexes
with some humate forms.
Both Fe uptake and transportation within plant organs are strongly affected by
several soil and plants factors. In general, a high degree of the oxidation of Fe compounds, Fe precipitation on carbonates and/or phosphates, and competition of trace
metal actions with Fe 2+ for the same binding sites of chelating compounds are responsible for a low Fe uptake and for the disturbance of its transport within plant organs.
Iron is considered to be the key metal in the energy transformation needed for
several live processes of plant cells. Its essential roles in the plant metabolism, presented in oversimplified and generalized forms, are as follows:
r Several Fe proteins, mainly transferrins, ferritins, and siderophores, are
involved in transport, storage, and binder systems.
r Fe occurs in heme and nonheme proteins and is concentrated in chloroplasts.
r Fe highly influences the formation of chlorophyll.
r Organic Fe complexes are involved in the electron transfer.
r Fe is directly implicated in the metabolism of nucleic acids.
r Both cations, Fe 2+ and Fe 3+ , play a catalytic role in various metabolic
processes.
Iron deficiency affects several physiological processes, and therefore retards plant
growth and yield. Its deficiency in several crops is now a major worldwide problem.