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| Last Updated:: 06/11/2018

Iron

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)
Source: https://www.google.co.in/search?hl=en&site=imghp&tbm
Treatment options for iron deficiency in trees and shrubs
Treatment Can be applied by homeowners? Applied by professional arborists? Recommended for large trees? Recommended for small trees and shrubs? Effects usually seen within: Effects of treatment last:
Foliar sprays
Chelated iron or manganese X X   X 1-2 weeks 1 Year
Ferrous or manganese sulfate X X   X 1-2 weeks 1 year
Implants/Injections
Medicaps X X X   1 month At least 2 years
Mediject X X     1 month At least 2 years
Mauget X X     1 month At least 2 years
Nutri-ject X X     1 month At least 2 years
Pressurized injection X X     1 month At least 2 years
Soil fertilizers
Chelated iron X X X X 1 month Variable
Soil acidifiers
Elemental sulfur X X   X 2-4 months Variable
Iron sulfate X X   X 2-4 weeks Variable
Source: http://www.extension.umn.edu/garden/yard-garden/trees-shrubs/iron-chlorosis/
Iron chlorosis
Iron chlorosis is a yellowing of plant leaves caused by Iron deficiency that affects many desirable landscape plants in Utah. The primary symptom of Iron deficiency is-
  • Interveinal chlorosis, the development of a yellow leaf with a network of dark green veins.
  • In severe cases, the entire leaf turns yellow or white and the outer edges may scorch and turn brown as the plant cells die.
  • It is common for an individual branch or one half of a tree to be chlorotic while the remainder of the tree appears normal.
  • In some areas vegetation from the entire landscape may be affected, while in others only the most susceptible plants show deficiency symptoms.
  • Yellow leaves indicate a lack of chlorophyll, the green pigment responsible for photosynthesis (sugar production) in plants.
  • Any reduction in chlorophyll during the growing season can reduce plant growth and vigor.
  • In addition, chlorotic plants often produce smaller fruits of poor quality with bitter flavor.
  • In severe cases, or if iron chlorosis persists over several years, individual limbs or the entire plant may die.
Source: city-and-town/tree-care
Causes of Iron chlorosis
The causes of iron chlorosis are complex and not clearly understood. Many reactions govern Iron availability and contribute to the complexity of Iron chemistry in soil. Iron chlorosis frequently occurs in soils that are alkaline (pH greater than 7.0) and that contain lime; conditions that are common in Utah. Most soils contain abundant levels of iron; however, deficiencies develop because soil chemical reactions render this iron unavailable to plants. At high soil pH, iron rapidly forms solids in combination with oxygen, and hydroxide and carbonate ions. These forms of iron are not water-soluble and cannot be absorbed by plant roots. Such iron will be tied up indefinitely unless soil conditions change. This also explains why rusty nails or iron shavings do not correct iron deficiency in Utah: iron released by these materials immediately forms solids that are unavailable to plants.
Source: publication/AG-SO-01.pdf
Prevention and control of Iron chlorosis
Control of Iron chlorosis is not easy and can be expensive. Therefore, one of the best methods is to select plant species and cultivars that are tolerant of high soil pH and less likely to be affected by low Iron availability. Table 1 describes the susceptibility of common landscape and crop plants to iron chlorosis. Planting selections from the highly susceptible column should be avoided in Utah, since recurring chlorosis problems will weaken the plants, predisposing them to other problems and/or shortening their life span.
Source: http://extension.usu.edu/files/publications
Susceptibility of plants to Iron deficiency
FRUITS, VEGETABLES AND FLOWERS
Highly susceptible Moderately susceptible Moderately tolerant
Berries Grapes Corn Turf grasses Flowers (some) Vegetables (some) Alfalfa Wheat, barley, and oats Potatoes
TREES AND SHRUBS
Highly susceptible Moderately susceptible Moderately tolerant
Red maple Aspen Ash
Silver maple Beech Boxelder
Pin oak Birch Catalpa
Sweetgum Cherry Kentucky coffeetree
Dawn redwood Peach Cottonwoods
Amur maple Magnolia Poplars
Bumald spiraea Most conifers Ginkgo
Azalea Mountain-ash Hackberry
Rhododendron London planetree Hawthorn
  Horsechestnut Honeylocust Linden Norway and Canyon maples Elms Most oaks
Some plants are listed under two categories because of differences among varieties and growing conditions.
Plant culture is also important in the control of iron chlorosis. Avoid saturated soil conditions by reducing watering or by installing drainage systems, especially with susceptible trees and shrubs. Aerate compacted areas around the base of affected vegetation. Also, avoid using plastic sheeting as mulch for susceptible plants, since it restricts oxygen movement into the soil.
Source: files/publications/publication
Several following methods are available for treating Iron deficiency
  • Soil application of elemental sulfur combined with ferrous (iron) sulfate.
  • Soil application of Iron chelates.
  • Foliar sprays containing ferrous sulfate or chelated Iron
  • Trunk injection of ferric Ammonium Citrate or Iron Sulfate (trees only).
Advantages and disadvantages of Iron chlorosis control methods
Method Advantages Disadvantages
Soil application of iron sulfate-elemental sulfur combination
  • Lasts up to several years
  • Relatively inexpensive
  • No injury to plant
  • Simple procedure
  • Slow response
  • Results sometimes variable
  • Too expensive for large areas of low-value crops
  • Can be labor-intensive
Soil application of iron chelates
  • Simple procedure
  • Generally no injury to plant
  • Relatively quick response
  • May last less than one season
  • Expensive
  • Results sometimes variable
Foliar application of chelates or iron sulfate
  • Quick response
  • Fairly simple, easy procedure (except for large trees)
  • Only practical method for field crops
  • Expensive on trees
  • Can cause temporary leaf burning
  • Often lasts less than one season
  • Provides only partial control
Trunk injection or implantation
  • Lasts up to several years
  • Moderate expense
  • Injures tree’s trunk
  • Can’t be used on shrubs or non-woody plants
  • Results sometimes variable
  • Can cause temporary leaf burning
  • Somewhat complicated procedure
Source: usu.edu/files/publications
Fe chelation and long distance Fe transport
Source: nih.gov/pmc/articles/PMC2
Once transported into the root epidermal cells, Fe is almost certainly chelated, although it is unclear by what. It is also unclear which transporter loads Fe into the xylem, but once in the xylem, Fe is known to be bound by citrate. Citrate itself is transported into the xylem via FRD3. YSLs in rice may transport Fe into the phloem, where it is likely bound by nicotianamine (NA). It has been proposed that NA may serve as a shuttle between the YSL transporters and an iron transport protein (ITP). NA is an essential part of long distance movement to the seeds, although it is unclear in what form the Fe is held, once it is loaded into the seeds. The ysl1, ysl3, and opt3 mutants all have decreased seed Fe content, suggesting that they load Fe into the seed.
Source: ncbi.nlm.nih
Transcriptional changes in response to Fe deficiency in specific root layers
Source: PMC2764373/figure/F1
  1. Root layers marked by propidium iodide staining of the cell wall (red) and expression of GFP in the stele and endodermis. Epi - epidermis, Cor - cortex, End - endodermis, Ste - stele, QC - quiescent center, Cei - cortex/endodermis initial.
  2. Enriched Gene-Ontology categories. miRNA, microRNA; RNase, Ribonuclease; GTPase, guanosine triphosphatase.
Source: http://extension.usu.edu