Major Micronutrients Present in Plant: 7 Micronutrients

Let us make an in-depth study of the sources, functions and deficiency symptoms of some major micronutrients present in plant.

The seven major micronutrients present in plant are: (1) Iron (2) Manganese (3) Molybdenum (4) Zinc (5) Copper (6) Boron and (7) Chlorine.

1. Iron (Fe):

Source:

Plant obtains iron in the form of ferrous ions (Fe²⁺) and ferric ions (Fe³⁺). Under conditions of iron stress, roots secrete legends for iron uptake, e.g. caffeic acid (in dicots and monocots) and phytosideropliores (grasses and cereals).

Regions of requirements:

It is required everywhere in the plant body. It collects specifically along leaf veins. It is required in large amounts (equal to 100 µg/g dry weight) in comparison to other micronutrients.

Functions:

(i) It is important component of proteins like ferrodoxin and cytochromes, involve in redox reactions

(ii) It activates catalase4 and oxidase

(iii) It is reversible oxidized from Fe²⁺ to Fe³⁺ during electron transfer

(iv) It is a constituent of leghaemoglobin found in root nodules of leguminous plants.

Deficiency Symptoms:

(i) Chlorosis of younger leaves

(ii) Under prolonged deficiency veins become chlorotic and the whole leaf gradually becomes white

(iii) Inhibits chloroplast formation.

2. Manganese (Mn):

Source:

Plants absorb manganese in the form of divalent manganous cation (Mn²+).

Regions of requirements:

It is required in leaves and seeds.

Functions:

(i) Form magnesium pectate of middle lamella

(ii) Activates many enzymes of TCA cycle (decarboxylases and dehydrogenases), photolysis of water and nitrogen metabolism.

Deficiency Symptoms:

(i) Chlorosis associated with necrotic spots develop in leaves,

(ii) Chloroplast become vacuolated and granular.

3. Molybdenum (Mo):

Source:

Plants absorb molybdenum in the form of molybdate ions (MoO₂²⁺). It is also absorbed in tri, tetra or pent-oxides.

Regions of requirements:

It is required everywhere in plant. MoO³⁺ ions are particularly required in roots.

Functions:

It is component of enzymes like nitrogenase and nitrate reductase of nitrogen metabolism.

Deficiency Symptoms:

(i) Slight retardation of growth

(ii) Whiptail disease in cabbage where young leaves become distorted.

(iii) Yellow spot disease of citrus where leaves develop mottled chlorosis and marginal wilting of leaves

(iv) Premature fall of flowers.

4. Zinc (Zn):

Source:

Plant absorb Zinc as divalent Zn²+ ion.

Regions of requirements:

Everywhere in a plant body.

Functions:

(i) It activates many enzymes such as dehydrogenases, carboxylases, etc.

(ii) Take part in the synthesis of auxin precursor i.e. tryptophan.

Deficiency Symptoms:

(i) Leaf distortion

(ii) Little leaf disorders of fruit trees,

(iii) Reduction in fruits

(iv) Stunted growth.

5. Copper (Cu):

Source:

Plants absorb Copper as Cupric ion (Cu²⁺).

Regions of requirements:

Everywhere in a plant body.

Functions:

(i) Like iron, copper is associated with enzymes involved in redox reactions, e.g plastocyanin and cytochrome oxidase,

(ii) Darkening of cut potato and apple is due to the polyphenol oxidase, a copper containing enzyme.

Deficiency Symptoms:

(i) Production of dark green leaves. Which may contain necrotic spots

(ii) Leaves become malformed

(iii) Leaves fall prematurely in extreme deficiency

(iv) Dieback of shoot in fruit trees

(v) Exanthema disease in tree when bark exudes gum

(vi) Blackening of potatoes.

6. Boron (B):

Source:

It is absorbed as divalent borate (B₄O₇^2-) and trivalent borate (BO₃^3-).

Regions of requirements:

In leaves and feeds.

Functions:

(i) Required for pollen germination, membrane function, cell differentiation

(ii) Also involved in carbohydrate translocation nucleic acid synthesis, hormone metabolism and fat metabolism.

Deficiency Symptoms:

(i) Block necrosis of young leaves and terminal buds

(ii) Stem becomes stiff and brittle

(iii) Stem become highly branched due to loss of apical dominance

(iv) Necrosis of root, fruits and tubers

(v) Abscission of flowers,

(vi) Absence of root nodules in leguminous plants

(vii) Internal tissues become corky.

7. Chlorine (CI):

Source:

Plants absorb it in the form of chloride anion (CI^–).

Regions of requirements:

Every part of a plant.

Functions:

(i) Required for cell division in both leaves and roots

(ii) Essential for water splitting reaction, which leads to oxygen liberation

(iii) Along with Na⁺ and K⁺, it determines solute concentration and anion-cation balance in cells.

Deficiency Symptoms:

(i) Wilting of leaf tips followed by leaf chlorosis and necrosis,

(ii) Stunted root growth and reduced fruiting.