The macronutrients are: carbon, hydrogen, oxygen, nitrogen, phosphorus, sulphur, potassium, calcium and magnesium.
Functions of carbon, hydrogen and oxygen :
These are the components of protoplasm and all organic componds found in plants.
Functions of nitrogen.
It plays a major constituent of proteins, nucleic acids, vitamins and hormones.
Functions of phosphorous.
Phosphate plays a key role in energy metabolism. Incorporated into ATP it is part and parcel of the universal energy currency of all types of living systems.
Fuctions of sulphur.
Sulphur is present in amino-acids - cysteine and methionine.
Why is that in certain plants deficiency symptoms appear first in younger parts of the plant while in others they do so in mature organs?
To find out if the deficiency symptom is due to the deficiency of which nutrient , in the case when more than one nutrient can cause the symptom, a number of wide mouthed bottles is taken. Each is fitted with split cork.
One of them has the normal culture and is called control. While the other bottles have deficiency of one mineral each. For example necrosis is caused by the deficiency of Ca, Mg or K.
Thus three bottles having defieciency of Ca, Mg and K respectively is taken and the plant is grown in each.
The plants in the three bottles are checked if they have developed chlorosis. If the symptom is corrected by the supply of the particular mineral. Then it is concluded that the deficiency was because of that mineral.
2. Die back: It is the withering of stem from apex downward. It is due to the deficiency of copper.
3. Necrosis : It is the death of the tissues. The leaf tips develop dead areas or necrotic areas. It may be also due to Ca, Mg, Ni, Cu and K.
4. Whiptail disease : It occurs in cauliflower. It is due to the deficiency of Mo.
5. Little leaf disease: It is due to the deficiency of Zn. It also causes rosette of apple and peaches.
Conditions for N2 fixation : There are following conditions necessary for N2 fixation :
(1) A strong reducing agent like NADPH : It supplies hydrogen to N2.
(2) ATP as source of energy : It provides energy. For fixation of NH3 molecules, 8 ATP molecules are needed.
(3) The enzyme system : Nitrogenase is necessary for N2 fixation.
(4) Compound for trapping ammonia : Ammonia is very toxic and needs to be trapped in the form of amino acids.
(5) Leghaemoglobin : It is O2 scavenger and maintains anaerobic environment otherwise in the presence of O2 the enzyme nitrogenase is toxicated.