- Autotrophs : An organism that synthesize its required nutrients from simple and inorganic substances.
- Heterotrophs : An organism that cannot synthesize its own nutrients and depend on others.
Essential Mineral elements :
- More than sixty elements found in different plants.
- Some plant accumulates selenium, some other gold.
Criteria for Essentiality :
- Element absolutely necessary for normal growth and reproduction.
- In the absence of the element the plant can not complete their life cycle.
- Role of the element can not be replaced by any other elements.
- The element must be directly involved in the metabolism of plant.
Macronutrients : are generally present in the plants tissues in large amount (in excess of 10 mmole
Kg-1 of dry matter).
Micronutrients : or trace elements are needed in very small amounts (less than 10 mmole Kg-1 of dry matter)
Four group of essential elements :
- As components of biomolecules and forms structural elements of cells (e.g. carbon, hydrogen, oxygen and nitrogen)
- As components of energy-related chemical compounds in plants. (magnesium in chlorophyll and phosphorous in ATP)
- Element that activate or inhibit enzymes (Mg2+, Zn2+)
- Alter the osmotic potential of a cell. (K+)
Role of macro and micro-nutrients :
Nitrogen :
- Absorbed in the form of NO2- or NH4+
- Required by meristematic tissue and metabolically active tissue.
- Constituent of proteins, nucleic acids, vitamins and hormones.
Phosphorus :
- Absorbed in the form of H2PO4- or HPO42-.
- Constituents of cell membrane certain proteins, all nucleic acids and required in phosphorylation reaction.
Potassium :
- Absorbed as potassium ion (K+)
- Required in meristematic tissues.
- Maintain cation and anion balance in cell.
- Opening and closing of stomata.
- Activation of enzyme.
- Maintenance of turgidity of cells.
Calcium :
- Absorbed in the form of calcium ions (Ca2+).
- Required by meristematic and differentiating tissues.
- Used in synthesis of cell wall particularly as calcium pectate in middle lamella.
- Required during formation of mitotic spindle.
- Involved in normal functioning of cell membrane.
- Activate certain enzyme.
- Important role in regulating metabolic activity.
