Micronutrients: Introduction, Iron, Copper, Manganese, Molybdenum, Nickel, Boron, Zinc, Chlorine, Practice Problems, FAQs

You all are growing and you know that we need a variety of nutrients to support our growth. Sometimes we may look dull and pale. Have you been ever told that you are anaemic? Doctors may tell you that you are anaemic because of iron deficiency. Do you know what are the common symptoms of iron deficiency? Yes, it includes dizziness, fatigue, fast heart rate, brittle nails, shortness of breath etc.

             Fig: Nutrient deficiency

You know, like humans and animals, plants do require proper nutrition for growth and development. They need two types of nutrients like macronutrients and micronutrients. You know like us they also develop some deficiency diseases. So if there is iron deficiency in plants how will we know? Yes, in plants, leaf veins become pale yellow or white. In severe cases the youngest leaves may show stunted growth or become pale. 

                                         Fig: Pale leaf

You know iron is considered a micronutrient. Micronutrients are essential plant nutrients that are found in small amounts in tissues, but play an imperative role in plant growth and development. Without these nutrients, plant nutrition would be affected leading to decline in the plant productivity. Let us understand more about micronutrients in detail in this article.

Table of contents

• Micronutrients
• Iron
• Copper
• Manganese
• Molybdenum
• Nickel
• Boron
• Zinc
• Chlorine
• Practice Problems
• FAQs

Micronutrients

Micronutrients are trace elements that are needed in very small amounts (less than 10 mmol Kg –1 of dry matter). These include manganese, iron, copper, zinc, boron, molybdenum, chlorine and nickel.

                                             Fig: Micronutrients

Iron

Iron is absorbed by plants in the form of ferric ions (Fe3+). It is reversibly oxidised from Fe2+ to Fe3+ during electron transfer. It activates catalase enzymes, and is essential for the formation of chlorophyll. It is part of ferredoxin, catalase, nitrogenase etc. It is required for the electron transport chain and light reaction of photosynthesis. 

Copper

It is absorbed as cupric ions (Cu2+). It is required for the overall metabolic activities in plants. It is associated with certain enzymes involved in redox reactions and is reversibly oxidised from Cu+ to Cu2+. It is part of the plastocyanin pigment of photosynthesis. It acts as an activator of enzymes like oxidases. 

Manganese

It is absorbed in the form of mangenous ions (Mn2+). It activates many enzymes that are involved in respiration, photosynthesis, and nitrogen metabolism. The best defined function of manganese is in the splitting of water (photolysis) to liberate oxygen during photosynthesis. It activates enzymes like malic dehydrogenase and oxalosuccinic dehydrogenase. 

Molybdenum

Plants obtain molybdenum in the form of molybdate ions (MoO2 2+). It is a component of several enzymes, including nitrogenase and nitrate reductase, both of which participate in nitrogen metabolism.

Nickel

Nickel is considered as a component of some plant enzymes. Examples include urease. This enzyme helps in the metabolism of nitrogen in urea. This nitrogen in urea is converted into usable ammonia within the plant. Without nickel, urea can accumulate into toxic levels.

Boron

Boron is absorbed as BO3 3− or B4O7 2− . Boron is required for uptake and utilisation of Ca2+, membrane functioning, pollen germination, cell elongation, cell differentiation and carbohydrate translocation.

Zinc

Plants obtain zinc as Zn2+ ions. It activates various enzymes, especially carboxylases and alcoholic dehydrogenases. It is also required for the synthesis of auxin hormone. 

Chlorine

It is absorbed in the form of chloride anion (Cl–). Along with Na+ and K+, it helps in determining the solute concentration and the anion cation balance in cells. It is essential for the water-splitting reaction in photosynthesis (photolysis), a reaction that leads to oxygen evolution. It helps in the transfer of electrons from water to photosystem II (PSII). It is also required for cell division and in both leaves and roots.

Practice Problems

Q 1. Which of the following statements is correct with regard to manganese toxicity?

a. Manganese toxicity can increase magnesium uptake and helps this to bind with the enzymes
b. Manganese toxicity inhibits calcium translocation in shoot
c. Manganese toxicity leads to increase in iron uptake
d. Manganese toxicity leads to stunted growth

Answer: Manganese (Mn) competes with elements such as iron, calcium and magnesium for absorption. Thus, excess of manganese may result in deficiency of magnesium, calcium and iron elements. Manganese is considered to inhibit translocation of calcium in the shoot region of the plants. Brown spots and chlorotic (yellow appearance) veins in the leaves occur due to manganese toxicity. Hence option b is correct.

Q 2. Which one of the following is odd with respect to micronutrients in plants?

a. Nickel
b. Iron
c. Calcium
d. Zinc

Answer: Based on the quantitative requirements of mineral elements by plants, essential elements have been divided into the following two broad categories:

• Macronutrients: These are present in plants in excess of 10 moles per kg of dry weight. They include the nine essential elements like carbon, oxygen, hydrogen, calcium, magnesium, nitrogen, phosphorus, sulphur, and potassium.
• Micronutrients: These are present in plants in quantities less than 10 moles per kg of dry weight. They include manganese, iron, zinc, copper, nickel, molybdenum, boron, and chlorine. Hence option c is correct.

 Q 3. Identify the incorrect match from the following:

a. Boron - Pollen germination
b. Molybdenum - Carbohydrate translocation
c. Chlorine - Helps in oxygen evolution
d. Zinc - Auxin synthesis

Answer: Chlorine helps determine solute concentration as well as ionic balance in cells along with sodium and potassium ions. It is also required for the water splitting reaction in photosynthesis that eventually leads to evolution of oxygen. 

Plants require boron for pollen germination, calcium uptake and its utilisation. It is also required for cell elongation, cell differentiation, proper functioning of the membrane and carbohydrate translocation. 

Several enzymes required for nitrogen metabolism such as nitrogenase and nitrate reductase contain molybdenum. Zinc activates enzymes like carboxylases and alcoholic dehydrogenases. It is involved in biosynthesis of hormones like auxin. Hence option b is correct. 

Q 4. Activation of catalase enzymes, formation of chlorophyll, electron transfer are all associated with which of the following elements?

a. Magnesium
b. Sulphur
c. Iron
d. Zinc

Answer: Zinc is absorbed by plants as divalent cation. It is normally involved in the synthesis of auxin hormone and activation of carboxylases. 

Magnesium is absorbed by plants as divalent cation. It is involved in the activation of enzymes of respiration, photosynthesis, DNA and RNA synthesis. It is a principle component of chlorophyll and it helps maintain ribosome structure. Hence option a is correct.

Sulphur is absorbed by plants as sulphate ion. It is found in 2 amino acids such as cysteine and methionine. It is considered as a principle component of vitamins, coenzymes, and ferredoxin.

Iron is normally obtained by plants in the form of ferrous ion. It is involved in the activation of catalase enzymes. It is required for the formation of chlorophyll and electron transfer proteins like ferredoxin and cytochromes.

Q 5. Write down the function of iron and copper as micronutrients in plants?

Answer: Iron activates catalase enzymes, and is essential for the formation of chlorophyll. Copper is considered important for the overall metabolic activities in plants. It is associated with certain enzymes involved in redox reactions and is reversibly oxidised from Cu+ to Cu2+.

Q 6. In which form do iron, copper, manganese and molybdenum are absorbed as micronutrients by plants?

Answer: Iron is absorbed by plants in the form of ferric ions (Fe3+), Copper is absorbed as cupric ions (Cu2+), Manganese is absorbed in the form of mangenous ions (Mn2+), and plants obtain molybdenum in the form of molybdate ions (MoO2 2+) .

1. What is the function of Zinc as micronutrients in plants?

Answer: Zinc activates various enzymes, especially carboxylases. It is also required for the synthesis of auxin hormone. 

FAQs

Q 1. How does chlorine function as micronutrients in plants?
Answer - Along with Na+ and K+, chlorine helps in determining the solute concentration and the anion cation balance in cells. It is essential for the water-splitting reaction in photosynthesis, a reaction that leads to oxygen evolution.

Q 2. Which are considered as the seventeen essential nutrients for plant growth?
Answer: Plants require seventeen essential elements for proper growth and development. They include hydrogen (H), carbon (C), nitrogen (N), oxygen (O), phosphorus (P), sulphur (S), calcium (Ca), potassium (K), magnesium (Mg), chlorine (Cl), boron (B), copper (Cu), manganese (Mn), molybdenum (Mo), iron (Fe), nickel (Ni), and zinc (Zn).

Q 3. In which way do micronutrients help the plant?
Answer: Micronutrients are required for strong and steady growth of crops. This can result in higher yields and good harvest quality. It maximises the genetic potential of the plant. Their presence has a great impact on fruit setting, root development, seed viability and grain filling. 

Q 4. Which nutrient deficiency can lead to yellowing of leaves?
Answer: Manganese deficiency can lead to yellowing of leaves. It is normally seen between the veins of new foliage.

Related topics