Iron For Plants: Why Do Plants Need Iron?

Iron For Plants: Why Do Plants Need Iron?

By: Anne Baley

Every living thing needs food for fuel to grow and survive, and plants are just like animals in this regard. Scientists have determined 16 different elements that are crucial to healthy plant life, and iron is a small but important item on that list. Let’s learn more about the function of iron in plants.

What is 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. So what is iron? The function of iron is to act much like it does in the human bloodstream — helping to carry important elements through a plant’s circulatory system.

Where to Find Iron for Plants

Iron for plants can come from a number of sources. Ferric oxide is a chemical present in soil that gives dirt a distinctive red color, and plants can absorb iron from this chemical.

Iron is also present in decomposing plant matter, so adding compost to your soil or even allowing dead leaves to collect on the surface can help to add iron to your plants’ diet.

Why Do Plants Need Iron?

Why do plants need iron? As previously stated, it’s mostly to help the plant move oxygen through its system. Plants only need a tiny amount of iron to be healthy, but that small amount is crucial.

First of all, 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.

Soil that is alkaline or has had too much lime added often causes an iron deficiency in the plants in the area. You can correct it easily by adding an iron fertilizer, or evening out the pH balance in the soil by adding garden sulfur. Use a soil test kit and speak with your local extension service for testing if the problem persists.

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Boron

A primary function of boron is related to cell wall formation, so boron-deficient plants may be stunted. Sugar transport in plants, flower retention and pollen formation and germination also are affected by boron. Seed and grain production are reduced with low boron supply. Boron-deficiency symptoms first appear at the growing points. This results in a stunted appearance (rosetting), barren ears due to poor pollination, hollow stems and fruit (hollow heart) and brittle, discolored leaves and loss of fruiting bodies.

Boron deficiencies are found mainly in acid, sandy soils in regions of high rainfall, and those with low soil organic matter. Borate ions are mobile in soil and can be leached from the root zone. Boron deficiencies are more pronounced during drought periods when root activity is restricted.

Copper is necessary for carbohydrate and nitrogen metabolism and, inadequate copper results in stunting of plants. Copper also is required for lignin synthesis which is needed for cell wall strength and prevention of wilting. Deficiency symptoms of copper are dieback of stems and twigs, yellowing of leaves, stunted growth and pale green leaves that wither easily.

Copper deficiencies are mainly reported on sandy soils which are low in organic matter. Copper uptake decreases as soil pH increases. Increased phosphorus and iron availability in soils decreases copper uptake by plants.

Iron is involved in the production of chlorophyll, and iron chlorosis is easily recognized on iron-sensitive crops growing on calcareous soils. Iron also is a component of many enzymes associated with energy transfer, nitrogen reduction and fixation, and lignin formation. Iron is associated with sulfur in plants to form compounds that catalyze other reactions. Iron deficiencies are mainly manifested by yellow leaves due to low levels of chlorophyll. Leaf yellowing first appears on the younger upper leaves in interveinal tissues. Severe iron deficiencies cause leaves to turn completely yellow or almost white, and then brown as leaves die.

Iron deficiencies are found mainly on high pH soils, although some acid, sandy soils low in organic matter also may be iron-deficient. Cool, wet weather enhances iron deficiencies, especially on soils with marginal levels of available iron. Poorly aerated or compacted soils also reduce iron uptake by plants. Uptake of iron decreases with increased soil pH, and is adversely affected by high levels of available phosphorus, manganese and zinc in soils.

Manganese is necessary in photosynthesis, nitrogen metabolism and to form other compounds required for plant metabolism. Interveinal chlorosis is a characteristic manganese-deficiency symptom. In very severe manganese cases, brown necrotic spots appear on leaves, resulting in premature leaf drop. Delayed maturity is another deficiency symptom in some species. White/gray spots on leaves of some cereal crops is a sign of manganese deficienc.

Manganese deficiencies mainly occur on organic soils, high-pH soils, sandy soils low in organic matter, and on over-limed soils. Soil manganese may be less available in dry, well-aerated soils, but can become more available under wet soil conditions when manganese is reduced to the plant-available form. Conversely, manganese toxicity can result in some acidic, high-manganese soils. Uptake of manganese decreases with increased soil pH and is adversely affected by high levels of available iron in soils.

Molybdenum is involved in enzyme systems relating to nitrogen fixation by bacteria growing symbiotically with legumes. Nitrogen metabolism, protein synthesis and sulfur metabolism are also affected by molybdenum. Molybdenum has a significant effect on pollen formation, so fruit and grain formation are affected in molybdenum-deficient plants. Because molybdenum requirements are so low, most plant species do not exhibit molybdenum-deficiency symptoms. These deficiency symptoms in legumes are mainly exhibited as nitrogen-deficiency symptoms because of the primary role of molybdenum in nitrogen fixation. Unlike the other micronutrients, molybdenum-deficiency symptoms are not confined mainly to the youngest leaves because molybdenum is mobile in plants. The characteristic molybdenum deficiency symptom in some vegetable crops is irregular leaf blade formation known as whiptail, but interveinal mottling and marginal chlorosis of older leaves also have been observed.

Molybdenum deficiencies are found mainly on acid, sandy soils in humid regions. Molybdenum uptake by plants increases with increased soil pH, which is opposite that of the other micronutrients. Molybdenum deficiencies in legumes may be corrected by liming acid soils rather than by molybdenum applications. However, seed treatment with molybdenum sources may be more economical than liming in some areas.

Zinc is an essential component of various enzyme systems for energy production, protein synthesis, and growth regulation. Zinc deficient plants also exhibit delayed maturity. Zinc is not mobile in plants so zinc-deficiency symptoms occur mainly in new growth. Poor mobility in plants suggests the need for a constant supply of available zinc for optimum growth. The most visible zinc deficiency symptoms are short internodes and a decrease in leaf size. Delayed maturity also is a symptom of zinc-deficient plants.

Zinc deficiencies are mainly found on sandy soils low in organic matter and on organic soils. Zinc deficiencies occur more often during cold, wet spring weather and are related to reduced root growth and activity as well as lower microbial activity decreases zinc release from soil organic matter. Zinc uptake by plants decreases with increased soil pH. Uptake of zinc also is adversely affected by high levels of available phosphorus and iron in soils.

Because chloride is a mobile anion in plants, most of its functions relate to salt effects (stomatal opening) and electrical charge balance in physiological functions in plants. Chloride also indirectly affects plant growth by stomatal regulation of water loss. Wilting and restricted, highly branched root systems are the main chloride-deficiency symptoms, which are found mainly in cereal crops.

Most soils contain sufficient levels of chloride for adequate plant nutrition. However, reported chloride deficiencies have been reported on sandy soils in high rainfall areas or those derived from low-chloride parent materials. There are few areas of chloride-deficient so this micronutrient generally is not considered in fertilizer programs. In addition, chloride is applied to soils with KCl, the dominant potassium fertilizer. The role of chloride in decreasing the incidence of various diseases in small grains is perhaps more important than its nutritional role from a practical viewpoint.

Plants differ in their requirements for certain micronutrients. The following table shows the estimate of the relative response of selected crops to micronutrients. The ratings of low medium and high are used to indicate the relative degree of responsiveness.

Table 1. Crop Response to Micronutrients


Background: Iron is an essential element for both plant productivity and nutritional quality. Improving plant iron content was attempted through genetic engineering of plants overexpressing ferritins. However, both the roles of these proteins in plant physiology, and the mechanisms involved in the regulation of their expression are largely unknown. Although the structure of ferritins is highly conserved between plants and animals, their cellular localization differs. Furthermore, regulation of ferritin gene expression in response to iron excess occurs at the transcriptional level in plants, in contrast to animals which regulate ferritin expression at the translational level.

Scope: In this review, an overview of our knowledge of bacterial and mammalian ferritin synthesis and functions is presented. Then the following will be reviewed: (a) the specific features of plant ferritins (b) the regulation of their synthesis during development and in response to various environmental cues and (c) their function in plant physiology, with special emphasis on the role that both bacterial and plant ferritins play during plant-bacteria interactions. Arabidopsis ferritins are encoded by a small nuclear gene family of four members which are differentially expressed. Recent results obtained by using this model plant enabled progress to be made in our understanding of the regulation of the synthesis and the in planta function of these various ferritins.

Conclusions: Studies on plant ferritin functions and regulation of their synthesis revealed strong links between these proteins and protection against oxidative stress. In contrast, their putative iron-storage function to furnish iron during various development processes is unlikely to be essential. Ferritins, by buffering iron, exert a fine tuning of the quantity of metal required for metabolic purposes, and help plants to cope with adverse situations, the deleterious effects of which would be amplified if no system had evolved to take care of free reactive iron.

Figures

Tissue-specific expression and developmental regulation…


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Institut für Pflanzenernährung, Stuttgart, Germany

Institut für Pflanzenernährung, Stuttgart, Germany

Institut für Pflanzenernährung, Stuttgart, Germany

Institut für Pflanzenernährung, Stuttgart, Germany

Summary

Micronutrients and macronutrients are elements with specific and essential physiological functions in plant metabolism. This chapter deals with the functions of the individual micronutrients and considers metals that function in plants by valency change (iron, manganese, copper, and molybdenum), metals in which valency changes do not occur (zinc), and then the nonmetals (boron, chlorine). Chloride can affect plant growth indirectly via stomatal regulation as a mobile counter anion for K + . Resupplying Mn to deficient plants reactivates photosynthetic O2 evolution within 24 hours, whereas ultrastructure and chlorophyll formation are more difficult to restore. The role of micronutrients in defense systems against pathogens deserves more attention in the future, as well as a better characterization of the “physiological active” fraction of micronutrients and the critical deficiency concentrations in meristematic tissues.


The Role of Iron in Energy Metabolism in Animals

Iron is essential for a wide variety of the metabolic processes of living organisms, due to its chemical transitional property: it has both ferrous (Fe2+) and ferric (Fe3+) states, which can donate and accept electrons, respectively. Iron is present in the different forms of heme and the iron-sulfur (Fe-S) .

Iron is essential for a wide variety of the metabolic processes of living organisms, due to its chemical transitional property: it has both ferrous (Fe2+) and ferric (Fe3+) states, which can donate and accept electrons, respectively. Iron is present in the different forms of heme and the iron-sulfur (Fe-S) cluster binding protein, which plays an important role in various enzymatic reactions such as aerobic respiration, TCA-cycle function and DNA synthesis as well as oxygen transport and storage.

2.7 billion years ago, the appearance of photosynthetic organisms made possible the subsequent evolution of systems that utilize glucose and produce ATP by oxidative phosphorylation using the pre-existing glycolytic pathway. Therefore, this evolution must be understood as a pivotal event. However, the failure of electron transport produces reactive oxygen species (ROS), therefore living organisms have developed anti-oxidant mechanisms against ROS by effective scavengers such as vitamins C and E or enzyme reaction by catalase, super oxide dismutase, glutathione peroxidase, etc. Although iron is tightly controlled, excess free iron (Fe2+) deteriorates oxidative stress to produce most toxic hydroxyl radical by Fenton reaction.

In this Research Topic, we seek articles that address the following aspects of the role of iron in animal energy metabolism:
• cellular and mitochondrial iron metabolism
• oxidative stress
• inherited disorders of iron metabolism
• cross-talk between iron metabolism and metabolic diseases such as diabetes and lipidosis

Keywords: electron transport system, Iron, mitochondria, oxidative stress, oxidative phosphorylation

Important Note: All contributions to this Research Topic must be within the scope of the section and journal to which they are submitted, as defined in their mission statements. Frontiers reserves the right to guide an out-of-scope manuscript to a more suitable section or journal at any stage of peer review.


Is Silicon Needed?

The research does show benefits of using silicon with certain agricultural crops (rice, wheat, sugarcane, etc.), especially if grown in poor quality soils however, there are only limited studies that indicate there may be benefits for greenhouse crops. For the crops tested, there may be benefit of using silicon for intermediate and accumulator plants. For non-accumulators, there is conflicting information as to whether they benefit. For example, tomato, which is a non-accumulator, had increased flowering and fruit set when given additional silicon. However, powdery mildew and nutrient toxicity studies showed there was no significant suppression of either in non-accumulators treated with silicon.

As stated above, crop inputs such as water, fertilizer and growing medium may supply sufficient silicon for non-accumulators and perhaps intermediate accumulators. If not, intermediate accumulators may benefit from additional supplementation with silicon. Unfortunately silicon is not tested by most labs, so it is unknown if a grower’s inputs already provide enough usable silicon to benefit crops.

Ed Bloodnick
Horticulture Director
US-South East

JoAnn Peery
Horticulture Specialist
US-Central, Canada-Central

Lance Lawnson
Horticulture Specialist
US-West, Canada-West

Troy Buechel
Horticulture Specialist
US-North East

Susan Parent
Horticulture Specialist
Canada-East, US-New England

Jose Chen Lopez
Horticulture Specialist
Mexico, Latin & South America

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  • Frantz, J.M., S. Khandahar and S. Leisner. 2011. Silicon differentially influences copper toxicity response in silicon-accumulator and non-accumulator species. J. Amer. Hort. Sci. 136:329-338.
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  • Newman, J. 2008. Supplementing silicon may yield benefits. GMPro Magazine: (6):74-76.
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