1. Manganese (Mn) :

Physiological role.
i.  As a Cofactor : Mangenese primarily functions as activator of several enzymes involved in photosynthesis. 

ii.  It helps in the splitting of water and liberation of oxygen 

iii. Synthesis of chlorophyll : It is also involved in the synthesis of chlorophyll.

Deficiency symptoms

Deficiency of manganese causes chlorosis, nacrosis in the interveinal areas of leaves, the veins remain green, the chloroplasts are devoid of chlorophyll and starch grains become yellow green in colour, vacuolated and finally disintegrate.

2. Copper :

Physiological role.

Copper is a component of many enzymes involved in redox reactions. It plays a as a key role in the electron transport chain in photosynthesis. 

Deficiency symptoms.

i. Deficiency of copper causes necrosis.

ii. Under severe conditions the whole plant may appear wilted and the leaves may be lost.

3. Zinc :

Physiological functions.
Zinc plays an important role in the activation of many enzymes especially carboxylases

It is involved in the synthesis of auxin. s

Deficiency symptoms.
Deficiency of zinc causes

(i) shortening of internodes with the result plant become stunted;

(ii) reduction in the size of leaves so that the leaves become very small.

(iii) chlorosis of older leaves starting at tip and extending to the margins.

Foliar Nutrition—In this type of process fertilizers, growth hormones, mineral nutrients and several other chemical substances are directly applied to the plants on their leaves. They are dissolved in water and sprayed on the leaves of plants. Such an application of nutrients is called foliar nutrition.

Advantages of Foliar Nutrition—The foliar nutrition has several advantages—

1. It reaches the desired tissues more quickly as compared to the soil nutrients. 

2. It is more economical means of fertilizing crop plants particularly costly micronutrients.

3. It is a useful method for accelerating growth and development during flowering and fruiting. 

(a) Reductive amination. In this process ammonia reacts with -Ketoglutaric acid and forms glutamic acid as indicated below : 

(b) Transamination. This process involves the transfer of amino groups from one amino acid to the keto group of a keto acid. Glutamic acid is the main amino acid from which the transfer of NH₂ group takes place and the other 17 amino acids are formed through transamination. The enzyme required for such raction is called transaminase.

(i) Macronutrients are generally present in plant tissues in large amounts in excess of 10m mole kg^–1 of dry matter. For example - Carbon, hydrogen, nitogen, phosphorous, and oxygen 

(b) Micronutrients : Micronutrients or trace elements are needed in less than 10mmole kg^–1  of dry matter eg. iron, manganese, copper, molybdenum, zinc, boron, chlorine and nickel.

(c) Toxic elements : Any mineral ion or element which reduces dry weight by 10% of plant is called toxic element. Toxicity of element differs from plant to plant. The elements when present in large amounts much more than what is needed becomes toxic. 

(d) Essential elements : These are the elements which are essential for the growth of the plants. The plant cannot complete their lifecycle in the absence of it.  They are C, H, O, N, P, S, K, Ca, Mg, Fe, Mn, Cu, Mo, Zn, B, CI and NL

(1) Nutrients. The chemical substance that works as a raw material for body building and maintaining its function is termed nutrient.

(2) Micronutrients. These are needed in very small amounts, equal to or less than 0. lmg per gram of dry matter.

(3) Macronutrients. These must be present in plant tissues in concentrations of 1 to 10 mg per gram of dry matter.

(4) Active absorption. It is the movement of ions or molecules against concentration gradient or towards concentration gradient by taking energy directly or indirectly through metabolism.

(5) Passive absorption. It is the movement of minerals from higher concentration to lower concentration by physical processes not involving direct expenditure of energy.

(6) Symplastic pathway. It is the movement of ions across the cytoplasm of cortex, endodermis of pericycle through plasmodesmata.