Essential Elements and the Growth of Plants

This article throws light upon the functions of various essential elements in the growth of plants. The essential elements are: 1. Carbon, Oxygen and Hydrogen 2. Nitrogen 3. Phosphorus 4. Potassium 5. Calcium 6. Magnesium 7. Sulphur 8. Iron 9. Manganese 10. Copper 11. Zinc 12. Molybdenum 13. Boron 14. Chlorine, Cobalt and Sodium.

1. Carbon, Oxygen and Hydrogen:

Carbon, oxygen and hydrogen are the major constituents of all organic compounds, of which crops are made and they are concerned with different metabolic reactions which are vital for the growth of plants. Carbohydrates fats and proteins are oxidized to liberate energy which is essential for all living organisms.

2. Nitrogen:

Nitrogen is a major structural constituent of the cell. It is also an essential constituent of metabolically active compounds like proteins, nucleic acids, chlorophyll, enzymes, adenosine di and triphosphates (A.D.P. and A.T.P.) hormones etc.

Chlorophyll is essential for photosynthesis; nucleic acids are essential for transfer of genetic information. Enzymes are biological catalysts. A.D.P. and A.T.P. are essential for energy transfer. Hormones are regulators of plant growth.

When excessive amounts of nitrogen all supplied to crops they become succulent when they are adversely affected by unfavourable factors like deficiency of water, high temperature, insect pests and diseases, lodging etc. Whenever nitrogen is deficient in soil, flower buds turn pale and are shed prematurely; fruits are poor in quality, size, and weight.

3. Phosphorus:

Phosphorus is a constituent of the cell nucleus, and metabolically active compounds like nucleic acids, adenosine di and triphosphate etc. Nucleic acids are essential for the transfer of genetic information and A.D.P. and A.T.P. are involved in energy transfer, A.D.P. is involved in basic reactions of photosynthesis.

Phosphorus is essential for cell division and development of the meristematic tissues at the growing points and for root growth. It offsets the harmful effects of excess nitrogen in plants.

4. Potassium:

Potassium plays a vital role in the formation of amino acids and proteins from ammonium ions, which are absorbed by roots, form the soil. It is also responsible for the transfer of carbohydrates, proteins etc. from the leaves to the roots. It also plays a vital role in the uptake of other elements particularly nitrogen, phosphorus and calcium. Potassium regulates the permeability of the cellular membrane.

It increases the hydration of protoplasm. It activates a number of enzymes, e.g. alcohol dehydrogenase and its deficiency decreases photosynthesis. Potassium increases the resistance of crops to hot and dry conditions and insect pests and diseases. It increases the stiffness of straw in cereals and therefore the lodging of cereals is reduced. It improves the quality of fruits and grains.

5. Calcium:

Calcium also regulates the permeability of the protoplasm and decreases the hydration of the protoplasm. Calcium is a structural component of chromosomes where it possibly binds the DNA to the protein; chromosomes are responsible for hereditary characters of crops.

Chromosomes become abnormal when calcium is deficient because mitosis is abnormal in the roots of calcium deficient plants and is not often followed by cell wall formation, resulting in two nuclei within the same cell.

It also activates enzymes e.g. Lipase. When calcium is applied to acid soils, the availability of nitrogen, phosphorus and molybdenum’s is increased. Crops cannot take enough potassium and magnesium from calcareous soils.

6. Magnesium:

Magnesium is a constituent part of chromosomes which are the bearers of hereditary characters. It is an essential constituent of polyribosomes involved in protein synthesis.

It is a constituent of chlorophyll. It affects the translocation of phosphorus in plants and activates enzymes e.g. pyro-phosphatase.

7. Sulphur:

Some proteins contain sulphur. Sulphur activates enzymes which participate in the dark reactions of photosynthesis. It affects the development of tissue. Xylem and collenchyma fibers thicken, resulting in a hard and woody stem.

8. Iron:

Iron is a structural part of both enzymes and their activators. It is a constituent of prophyrin compounds which include cytochromes, ferredoxin, hemoglobin etc.

The cytochromes participate in respiration during which electrons flow along the cytochromes bridge between the inner layer of the protoplasm and the outer layer of protoplasm and the anions flow in the opposite direction when iron is alternately oxidized to the ferric state and reduced to the ferrous state.

By being a structural constituent of cytochrome, B₆ and ferredoxin iron play direct role in photosynthesis and nitrogen fixation by Rhizobium bacteria found within the root nodules of leguminous plants, which, in turn, contain a red substance called leghaemoglobin.

9. Manganese:

Manganese is a constituent of nitrite reductaseand hydroxylamine reductase, which reduce nitrite and hydroxylamine respectively to ammonia, which is later converted to amino acids and proteins.

It also activates enzymes. Manganese deficiency reduces photosynthesis even when the chlorophyll content is not reduced.

10. Copper:

Copper is a constituent of several oxidation and reduction enzymes; photosynthesis is reduced when copper is deficient even when their chlorophyll content is not reduced. Copper deficiency adversely affects respiration.

11. Zinc:

Zinc is a constituent of enzymes. When zinc is deficient, photosynthesis is reduced even when the chlorophyll content is not reduced.

When it is deficient, the auxin, concentration is reduced and flowering and fruit formation is reduced and delayed.

12. Molybdenum:

Molybdenum is a constituent of the enzyme nitrate reductase which reduces nitrate to nitrite. It is essential for nitrogen fixation by free living bacteria e.g. Azotobacter, algae and symbiotic bacteria.

13. Boron:

Boron is required for proper development of tissues, particularly the vascular elements. Boron deficiency causes the necrosis of tissues and sterility and malformation of the reproductive organs. It is also involved in the translocation of sugars in plants.

14. Chlorine, Cobalt and Sodium:

Chlorine is involved in the evolution of oxygen in the primary reactions of photosynthesis. Cobalt is essential for micro-organisms e.g. rhizobium bacteria. It is a structural component of vitamin B₁₂. Sodium maintains a high internal osmotic concentration in plants, which enables them to withstand desiccation when the soil solution contains high amounts of salts.