Mineral Nutrition In Plants

Mineral : Mineral is any substance which is required by plants for physiological functioning and it is mostly taken from the soil.

What are Essential Elements ?

Any element that is important for a physiological role in plant and the absence of this element prevents the plant from completing its life cycle is an essential element.

According to Arnon and Stout three criteria must be met for an element to be considered essential, these are:

1. A plant must be unable to complete its life cycle in the absence of the essential element.
2. The function of the essential element cannot be replaced by another element i.e. deficiency of any one element cannot be met by supplying other element.
3. The essential element must be directly involved in plant metabolism.

Essential elements are divided into two categories : Macroelements and Microelements

Macroelements: The mineral/element is required in large quantity, conc > 1ppm. Also known as major elements. Macroelements consists of Phosphorous (P), Potassium (K), Silicon (Si), Nitrogen (N), Sulphur (S), Oxygen (O), Calcium (Ca), Magnesium (Mg), Carbon (C), Hydrogen (H).

Microelements: The mineral/element is required in less quantity, conc < 1ppm. Also known as trace elements. Microelements consists of Ferrous (Fe), Nickel (Ni), Molybdenum (Mo), Copper (Cu), Zinc (Zn), Chlorine (Cl), Manganese (Mn), Sodium (Na), Boron (B).

Carbon and Oxygen can be obtained from air, Hydrogen can be obtained from water and hence Carbon, Oxygen and Hydrogen are known as Non-mineral Element. Rest all elements are obtained from soil.

Elements are categorized as mobile and immobile elements based on their mobility

Mobile Elements: Minerals that can readily move from one plant part to another are termed as mobile elements. Nitrogen (N), Phosphorous (P), Potassium (K), Chlorine (Cl), Sodium (Na), Zinc (Zn), Molybdenum (Mo) are Mobile Elements.

Immobile Elements: Minerals that cannot move from one part of the plant to another are termed as Immobile Elements. Calcium (Ca), Ferrous (Fe), Sulphur (S), Boron (B), Copper (Cu) are Immobile elements.

Deficiency of mobile elements leads to symptoms observed in Older leaves first. In the older leaves biomolecules containing these elements are broken down, making these elements available for younger leaves.

Deficiency of immobile elements leads to symptoms observed in Younger leaves first.

Group Categories of Elements:

All the above mentioned elements except for non-mineral elements are divided into 4 categories

Group I - Nitrogen (N), Sulphur (S)

Group II - Phosphorous (P), Boron (B), Silicon (Si)

Group III - Calcium (Ca), Potassium (K), Magnesium (Mg), Chlorine (Cl), Manganese (Mn), Sodium (Na)

Group IV - Ferrous (Fe), Zinc (Zn), Copper (Cu), Nickel (Ni), Molybdenum (Mo)

Group I Elements:

1) Nitrogen:

    Function: Protein synthesis, formation of protoplasm, nucleic acids, purine and pyrimidine bases, chlorophyll, alkaloids, NAD and NADP coenzymes, etc.

    Deficiency symptoms: 

• Chlorosis (yellowing of leaves) in older leaves 
• Anthocyanin accumulation in veins of leaves, petioles and stems due to which they become purple or red in colour.
• Stunted growth of plant.
• Late or less or no flowering.

Chlorosis in Leaf

Left - Healthy Leaf, Right- Leaf suffering from Chlorosis.

Anthocyanin accumulation in Leaf

Upper Leaves - Accumulation of anthocyanin

Lower Leaves - Healthy Leaves

2) Sulphur:

    Function: Component of sulphur containing amino acids like cystine, cysteine and methionine

                      Component of vitamins like thiamine and biotin.

    Deficiency Symptoms:

• Hinderance in chlorophyll formation, leads to chlorosis in younger leaves.
• Anthocyanin accumulation in stems and leaves.
• Retards cell division and growth.

Group II Elements:

1) Phosphorous:

    Function: Used in synthesis of nucleoproteins, Formation of ATP, NAD and NADP.

    Deficiency Symptoms:

• Delayed maturation of plants
• Premature falling of leaves
• Dead necrotic spots on leaves.
• Anthocyanin accumulation.

2) Silicon:

    Function: Prevents the plants from developing fungal infection, enhances growth, prevents the plant from lodging 

    Deficiency Symptoms:

• Fungal infection in plants
• weak stems
• lodging (permanent displacement of crop stems from their vertical position as a result of stem buckling or root displacement)

Left Pot: Normal Plant

Right Pot: Plant showing lodging

3) Boron:

    Function: Helps in metabolism of nitrogen, phosphorous, fats and hormones. Helps in the transport of sugar in phloem, helps in absorption of salts.

    Deficiency Symptoms:

• Death of shoot and root apex
• Stem becomes brittle.
• Accumulation of carbohydrate and amino acids in leaves.
• Causes heart rot disease in sugarbeet which leads to disintegration and browning of internal tissue
• Size of root cells is reduced.

Group III Elements:

1) Potassium:

    Function: Component of enzyme in respiration and photosynthesis, maintains the water balance.

   

    Deficiency Symptoms:

• Mottled chlorosis (leaves become yellow at the margins
• Internodes are short, the stem becomes slender and weak
• Leaves roll inwards
• leaf wilting and abscission

Wilting of Leaves

2) Calcium:

     Function: main constituent of middle lamella of cell wall, helps in metabolism of fats, helps in 

                       transportation of carbohydrates and fats.

     Deficiency Symptoms:

• Chlorosis at leaf tips
• Poor development of root and root hairs
• Necrosis in young leaves.
• Cell wall id weak

3) Magnesium:

     Function: Formation of chlorophyll, enzyme regulation, fat synthesis and nucleoprotein synthesis

     Deficiency Symptoms:

• Cell size is reduced
• Necrotic spots on leaves
• Reduction in fat synthesis and nucleoprotein synthesis

4) Chlorine:

     Function: Helps in cell division and water splitting reaction of photosynthesis

     Deficiency Symptoms:

• Stunted growth of plant
• Swelling of root tips
• Chlorosis and Necrosis in leaves

5) Manganese:

     Function: Activates the enzymes of Krebs Cycle, acts as cofactor in oxidative phosphorylation

     Deficiency Symptoms:

• Interveinal chlorosis and necrosis of leaves
• Browning of roots and leaves
• Growth retardation 

6) Sodium:

    Function: Enhances the growth of plant, aids in metabolism 

    Deficiency Symptoms: 

• Flowering of plant is inhibited
• Chlorosis and necrosis of leaves

Group IV Elements:

1) Iron:

    Function: Helps in formation of important respiratory enzymes and coenzymes, formation of ferridoxin

    Deficiency Symptoms:

• Interveinal chlorosis
• Protein synthesis is stopped
• Respiration rate is reduced

2) Zinc:

    Function: Synthesis of tryptophan and auxins-IAA (indole-3-acetic acid), formation of the enzyme carbonic anhydrase, protein synthesis.

    Deficiency Symptoms:

•  Decrease in protein synthesis
• Interveinal chlorosis
• Necrotic spots in older leaves
• Causes rosette disease of walnut, mottled leaf disease of walnut and apple, and white bud disease of maize.

3) Copper:

    Function: Biosynthesis of chlorophyll, catalyst in oxidation process, helps in absorption of CO2  and photosynthesis

    Deficiency Symptoms:

• Necrotic spots on tips or margins of young leaves
• Twisted or malformed leaves
• leaf abscission

4) Nickel:

    Function: Formation of urease

    Deficiency Symptoms:

• Leaf tip necrosis
• Urea accumulation in leaves which is toxic

5) Molybdenum:

    Function: Activation of nitrate reductase enzyme, controls the synthesis of ascorbic acid

    Deficiency Symptoms:

• Marginal Necrosis
• Flowering inhibited
• Wilting of leaves in severe condition

Marginal Necrosis