Essential elements are classified as Macronutrients, Micronutrients and Unclassified minerals based on their requirements. Essential minerals which are required in higher concentration are called Macronutrients. Essential minerals which are required in less concentration called are as Micronutrients.
of essential nutrients but are required by some plants, these minerals are placed in the list of unclassified minerals. These minerals play specific roles for example, Silicon is essential for pest resistance, prevent water lodging and aids cell wall formation in Equisetaceae (Equisetum), Cyperaceae and Gramineae (Table 12. 1).
12.1.2 Classification of minerals based on mobility
If you observe where the deficiency symptoms appear first, you can notice differences in old and younger leaves. It is mainly due to mobility of minerals. Based on this, they are classified into 1. Actively
mobile minerals and 2. Relatively immobile minerals (Figure 12.1).
a. Actively mobile minerals
Nitrogen, Phosphorus, Potassium,Magnesium, Chlorine, Sodium, Zinc and Molybdenum.
Deficiency symptoms first appear on old and senescent leaves due to active movement of minerals to younger leaves.
b. Relatively immobile minerals
Calcium, Sulphur, Iron, Boron and Copper shows deficiency symptoms first that appear on young leaves due to the immobile nature of minerals
12.1.3 Classification of minerals based on their functions
a. Structural component minerals: Minerals like Carbon, Hydrogen,Oxygen and Nitrogen
b. Enzyme function: Molybdenum (Mo) is essential for nitrogenase enzyme
during reduction of atmospheric nitrogen into ammonia. Zinc (Zn) is an important activator for alcohol dehydrogenase and carbonic anhydrase. Magnesium (Mg) is the activator for RUBP carboxylaseoxygenase and PEP carboxylase.
Nickel (Ni) is a constituent of urease and hydrogenase.
c. Osmotic Potential: Potassium (K) plays a key role in maintaining osmotic potential of the cell. The absorption of water, movement of stomata and turgidity are due to osmotic potential.
d. Energy components: Magnesium (Mg) in chlorophyll and phosphorous (P) in ATP.
12.2 Functions, mode of absorption and deficiency symptoms of macronutrients
Macronutrients, their functions, their mode of absorption, deficiency symptoms and deficiency diseases are discussed here:
1. Nitrogen (N): It is required by the plants in greatest amount. It is an essential component of proteins, nucleic acids, amino acids, vitamins, hormones, alkaloids, chlorophyll and cytochrome. It is absorbed by the
plants as nitrates (NO3).Deficiency symptoms: Chlorosis, stunted growth, anthocyanin formation.
2. Phosphorus (P): Constituent of cell membrane, proteins, nucleic acids, ATP, NADP, phytin and sugar phosphate. It is absorbed as H2PO4 + and HPO4 - ions.Deficiency symptoms: Stunted growth, anthocyanin formation, necrosis, inhibition of cambial activity, affect root growth and fruit ripening.
3. Potassium (K): Maintains turgidity and osmotic potential of the cell, opening and closure of stomata, phloem translocation, stimulate activity of enzymes, anion and cation
Deficiency symptoms: Chlorosis,anthocyanin formation, stunted growth, rolling of leaf tip and reduced nodulation in legumes.
