EIACP Centre on Plants and Pollution

Iron (Fe)

Iron (Fe) deficiency is a plant disorder also known as "lime-induced chlorosis". It can be confused with manganese deficiency. A deficiency in the soil is rare but iron can be unavailable for absorption if soil pH is not between about 5 and 6.5. A common problem is excessive alkalinity of the soil (the pH is above 6.5). Also, iron deficiency can develop if the soil is too waterlogged or has been overfertilised. Elements like Calcium, Zinc, Manganese, Phosphorus, or Copper can tie up iron if they are present in high amounts. Iron is needed to produce chlorophyll, hence its deficiency causes chlorosis. For example, iron is used in the active site of glutamyl-tRNA reductase, an enzyme needed for the formation of 5-Aminolevulinic acid which is a precursor of heme and chlorophyll.

Source: www.Iron_deficiency_(plant_disorder)

Iron and its Function

The role of iron in plants is as basic as it can get: without iron a plant can’t produce chlorophyll, can’t get oxygen and won’t be green. The function of iron is to act much like it does in a human bloodstream — helping to carry important elements through a plant’s circulatory system.

Iron transport in rice

Rice takes up iron from the soil as Fe³⁺ deoxymugineic acid (DMA) by the OsYSL15 transporter. Rice also uses the OsIRT1 transporter to take up Fe²⁺, which is abundant in submerged and anaerobic conditions. DMA, which is the primary phytosiderophore that aids in iron transport, is synthesized from S-adenosyl methionine through three sequential enzymatic reactions mediated by nicotianamine synthase (NAS), nicotianamine aminotransferase (NAAT), and DMA synthase (DMAS), and then secreted by the efflux transporter TOM1 to solubilize iron in the soil. Nicotianamine, which is the biosynthetic precursor of DMA, is a chelator of divalent metals and plays a part in translocation of metals within plants. Nicotianamine is secreted into the cell wall by the nicotianamine efflux transporter ENA1. The iron–nicotianamine transporter OsYSL2 mediates iron influx into rice grains. The photograph shows iron staining (blue coloration) of a rice seed (inset shows rice seeds). Iron is mainly localized to the embryo and the outer layers of the grain.

Source: http://www.nature.com/nature/journal/v497/n7447/fig_tab/nature11909_F4.html

Iron and Plants

Iron is an important micronutrient used in respiration, enzyme production, and chlorophyll synthesis. Plants will absorb iron both through their roots and leaves. As a nutrient, iron is most useful to plants in the ion form Fealthough in the presence of oxygen it converts into Fe3+, which is difficult for plants to assimilate. This problem can be overcome by using chelates or chelated iron. Iron is involved when a plant produces chlorophyll, which gives the plant oxygen as well as its healthy green color. This is why plants with an iron deficiency, or chlorosis, show a sickly yellow color to their leaves. Iron is also necessary for some enzyme functions in many plants.

Source: http://www.gibellaquarium.us/aquarium-plants-4/macronutrients.html

Distribution of Iron in Plants

Iron uptake by plants is fastest when iron is present in the ferrous form . In anaerobic soils, high concentrations of ferrous ions may lead to iron toxicity via excessive iron uptake. Plants may limit iron uptake under those conditions by the oxidation of ferrous ions with oxygen, which is transported from the shoot via aerenchyma (Foy et al., 1978). Iron in aerobic soils is mainly present as the ferric ion in precipitates (Lindsay et al., 1982)or in soluble chelates (Powell et al., 1980). Chaney et al. (1972) reported that dicotyledonous plants might enhance their capacity for iron uptake, in response to a developing deficiency, by increasing their ability to reduce ferric chelates at the root surface.

Source: http://www.agrsci.jp/ras/article/view/12/25

Model of acquisition and transport of iron in plants with an emphasis on changes of the iron-binding forms.

Source: http://www.ipk-gatersleben.de/fileadmin/_processed_/6/3/csm_933067_d125fc20c8.jpg

Iron Toxicity

Iron toxicity is not common, but some plants do secrete acids from the roots, which lowers soil pH. These plants can take up too much iron, leading to toxicity. The symptoms of iron toxicity include bronzing and stippling of leaves. The leaf discoloration is caused by the plant creating enzymes to control free radicals that are present in high iron levels. Some plants that are prone to iron toxicity include tomatoes, basil, phlox and impatiens.

Iron toxicity on marigold

Source: https://negreenhouseupdate.info/photos/iron-toxicity-marigold

Cause of Iron Toxicity and Prevention

Iron toxicity also can occur when chelated iron is added to soil. Chelates help increase nutrient uptake and solubility of metal micronutrients, which in turn makes over-absorption possible. To avoid iron toxicity, check pH balance and maintain a pH level of 5.8 or higher when growing plants prone to iron toxicity; use a fertilizer with a balanced ratio of manganese and iron; and use iron chelates carefully.

Source: http://homeguides.sfgate.com/effect-excess-iron-plants-48927.html

Symptoms of Iron deficiency:

• Leaves turning yellow or brown in the margins between the veins which may remain green, while young leaves may appear to be bleached.
• Fruit would be of poor quality and quantity.
• Any plant may be affected, but Raspberries and Pears are particularly susceptible, as well as most acid-loving plants such as azaleas and camellias.

Source: https://en.wikipedia.org/wiki/Iron_deficiency_(plant_disorder)