ROLE OF ESSENTIAL PLANT NUTRIENTS

ROLE OF ESSENTIAL PLANT NUTRIENTS

Introduction

Essential plant nutrients are 17 in number and these are based on criteria for essentiality. The total essential elements are further divided into two broad categories based on their quantitative requirements.

1. Macronutrients and
2. Micronutrients

Macronutrients are required in large quantities and these are: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Phosphorous (P), Sulphur (S), Potassium (K), Calcium (Ca) and Magnesium (Mg). Of these, carbon, hydrogen and oxygen are mainly obtained from CO2 and H2O, while the others are absorbed from the soil as mineral nutrition.

Micronutrients or trace elements, are needed in very small amount, generally less than 1ppm. These include Iron (Fe), Manganese (Mn), Copper (Cu), Molybdenum (Mo), Zinc (Zn), Boron (B), Chlorine (Cl) and Nickel (Ni).

 

Role of Essential Plant Nutrients

Essential elements perform several functions. They participate in various metabolic processes in the plant cells e.g., maintenance of osmotic concentration of cell sap, electron transport systems, energy transformation, buffering action, enzymatic activity etc.

Various forms and functions of essential nutrient elements are given below.

1. Nitrogen

It is required by all parts of a plant particularly the meristematic tissues and the metabolically active cells. Generally, it is required in the greatest amount. Its content in healthy plants ranges between 1-5% upon the species and variety.

• It is absorbed mainly as NO3^– though some are also taken up as NO₂^– or NH⁴⁺ means both cation as well as anion.
• Nitrogen is one of the major constituents of proteins, nucleic acids, amino acids, chlorophyll, phospholipids, alkaloids, enzymes, vitamins and hormones.
• It imparts dark green colour to plants, improves quality and succulence of leafy vegetables and fodder crops.

 

2. Phosphorus

Phosphorus is absorbed by the plants from soil in the form of phosphate ions depending upon pH of soil. When soil is acid, it is available as H₂PO₄^–, at neutral pH available as HPO₄^2- and when alkalinity is more means high pH, it is available as PO₄^3-. This is because of in high acidic condition, Fe and Al antagonize the uptake of “P” and in alkaline condition, Ca antagonize the uptake of “P”.

• Phosphorus is a constituent of cell membranes, certain proteins, all nucleic acids and nucleotides, and is required for all phosphorylation reactions (ATP).
• It is essential of reproductive functions, counteracts the excess N, enhance the activity of Rhizobia and root nodules and increase the ratio of grain/bhusa.
• It also provides rapid and vigorous growth to plants and decrease lodging tendency.
• It is called key to life as plants can’t complete their life cycle without P. it governs the root growth.

 

3. Potassium

It is present in a plant in a state of solution in cell sap and absorbed as potassium ion (K⁺). In plants, this is required in more abundant quantities in the meristematic tissues, buds, leaves and root tips.

• Potassium helps to maintain an anion-cation balance in cells and is involved in protein synthesis, opening and closing of stomata, activation of enzymes and in the maintenance of the turgidity of cells.
• It imparts disease resistance, essential in the formation and transfer of starches and sugars thus required in large quantity for potato, sweet potato, turnip, banana etc.
• It also improves the quality of tobacco leaf, quality of fibre, size and keeping quality of fruits.
• Potassium is acts as traffic policeman, root booster, food former, sugar and starch transporter, breathing regulator, protein builder etc. however, it is not seen effective in absence of N & P.
  

 

4. Calcium

Calcium is required by meristematic and differentiating tissues.

• During cell division it is used in the synthesis of cell wall, particularly as calcium pectate in the middle lamella. It provides turgidity of cell and is involved in the normal functioning of the cell membranes
• It is also needed during the formation of mitotic spindle.
• It accumulates in older leaves. It activates certain enzymes and plays an important role in regulating metabolic activities.

 

5. Magnesium

It is absorbed by plants in the form of divalent Mg²⁺.

• It activates the enzymes of respiration, photosynthesis and are involved in the synthesis of DNA and RNA.
• Magnesium is a constituent of the ring structure of chlorophyll, chromosomes and helps to maintain the ribosome structure.
• It is the carrier of “P” in plants, promotes formation of oil and fats, translocation of starches, catalytic action.

 

6. Sulphur

Plants obtain Sulphur in the form of sulphate.

• Sulphur is present in two amino acids – cysteine and methionine and is the main constituent of several coenzymes, vitamins (thiamine, biotin, Coenzyme A) and ferredoxin.
• It is associated with aromatic compounds and creates fragrance, aroma and smell.
• Helps in chlorophyll formation, promotes nodule formation and involved in tertiary structure of enzymes and proteins.

 

7. Iron

Plants obtain iron mainly in the form of ferric ions (Fe₃⁺) but physiologically active in Fe²⁺ (root site). It is reversibly oxidised from Fe²⁺ to Fe₃⁺ during electron transfer. It is required in larger amounts in comparison to other micronutrients.

• It is an important constituent of proteins involved in the transfer of electrons like ferredoxin and cytochromes.
• It activates catalase enzyme, and is essential for the formation of chlorophyll, acts as oxygen carrier.

 

8. Manganese

It is absorbed in the form of manganese ions (Mn²⁺).

• It activates many enzymes involved in photosynthesis, respiration and nitrogen metabolism.
• The best-defined function of manganese is in the splitting of water to liberate oxygen during photosynthesis.
• Associated with Fe metabolism, protects the structure of chloroplast as it helps in production of super oxide dismutase (SOD) which protects the chloroplast membrane from free radicles of O₂, essential for hill reaction, counteracts the bad effects of poor aeration.

 

9. Zinc

It activates various enzymes, especially carboxylases. It is also needed in the synthesis of auxin, production of SOD, essential for water uptake.

 

10. Copper

It is essential for the overall metabolism in plants. Like iron, it is associated with certain enzymes involved in redox reactions and is reversibly oxidised from Cu⁺ to Cu₂⁺. Also involved in production of SOD and flowers, required in flowering and development of grain.

11. Boron

Boron is required for uptake and utilisation of Ca₂⁺, acts as regulator of K/Ca ratio, membrane functioning, reproduction of plants & pollen germination, cell elongation, cell differentiation and carbohydrate translocation. It is primarily needed to maintain the apical growing point, concerned with buffer action, helps in active salt absorption, hormone movements, “N” & carbohydrate metabolism.

 

12. Molybdenum

It is a component of several enzymes, including nitrogenase and nitrate reductase both of which participate in nitrogen metabolism. Obvious role in N-fixation.

 

13. Chlorine

Along with Na⁺ and K⁺, it helps in determining the solute concentration and the anioncation balance in cells. It is essential for the water-splitting reaction in photosynthesis, a reaction that leads to oxygen evolution.

14. Nickel

 It is essential for hydrogenase, methyl reductase and urease activities that regulates N-metabolism. It is also needed for grain filling and seed vitality.

Read also…
MINERAL NUTRITION- AN OVERVIEW
NITROGEN FIXATION-DEFINITION, PROCESS& TYPES