Iron toxicity

In botany, iron toxicity refers to the exposure of plants to excessive absorption of iron compounds due to a high concentration in the soil .

Iron is an essential trace element in plant organisms. It affects photosynthesis and the formation of chlorophyll and carbohydrates . However, if iron is present in high concentrations in the soil, in a soluble form that can be absorbed by plants , the iron overload can damage the plant. Iron toxicity manifests itself in brown, bronze to yellow discoloration of the older leaves, beginning at the tips of the leaf surfaces.

causes

At normal pH values, iron is present in soils as iron (III) hydroxide Fe (OH) ₃ . Under anaerobic conditions, i.e. when the soil oxygen content is low, for example due to soil compaction or emersed conditions, iron (III) (Fe ³⁺ ) is reduced to iron (II) (Fe ²⁺ ). This brings the iron into a soluble form that is available to the plant.

${\displaystyle \mathrm {Fe(OH)_{3}+3\ H^{+}+e^{-}\longrightarrow Fe^{2+}+3\ H_{2}O} }$

Within the plant cell, an increased accumulation of Fe ²⁺ triggers the formation of reactive hydroxyl radicals according to the Fenton reaction .

${\displaystyle \mathrm {Fe^{2+}+H_{2}O_{2}\longrightarrow Fe^{3+}+\cdot OH+OH^{-}} }$ (Fenton reaction)

These reactive oxygen species lead to oxidative stress in the cell and to damage to the cellular and extracellular macromolecules. Iron toxicity is particularly known in rice-growing areas . Plants that are adapted to aquatic locations have developed protective systems that allow iron to be oxidized in order to avoid iron toxicity.

application

Plants without a covering tissue , such as mosses and lichens , are particularly sensitive to increased iron (II) concentrations. Therefore, Fe ²⁺ -containing herbicides are used to kill these plants.

See also

• For the iron metabolism in the human organism, see Iron Metabolism .

literature

• Mathias Becker, Folkard Asch: Iron toxicity in rice, conditions and management concepts , In: Journal of Plant Nutrition and Soil Science , Volume 168, 2005, pp. 558-573
• Günter Fellenberg: Chemistry of environmental pollution , 3rd edition, Verlag B. G. Teubner, Stuttgart 1997, ISBN 3-519-23510-2
• Klaus Prade: Influence of nutrient supply on iron toxicity in wet rice (Oryza sativa L.) in Basse Casamance, Senegal , Diss., Hochschulverlag Freiburg (Breisgau) 1987, ISBN 3-8107-2220-0

Individual evidence

1. ↑ Entry on iron. In: Römpp Online . Georg Thieme Verlag, accessed on February 11, 2015.
2. ^ ^{A b} Günter Fellenberg: Chemistry of environmental pollution . 3rd edition, Verlag B. G. Teubner, Stuttgart 1997, p. 158.
3. ↑ Ulrich Eckhardt: Investigations on iron assimilation in plants . Diss., Humboldt University, Berlin 2000.