Deficiency symptoms of Nitrogen:
1. Deficiency of nitrogen interferes with protein synthesis and hence all forms of growth are affected.
2. An early symptom is yellowing of leaves and development of chlorosis.
3. Older leaves turn light brown in colour and gradually dry.
4. Flowering is delayed or completely suppressed.
Deficiency symptoms of Phosphorous :
The deficiency of phosphorus causes :
1. disruption of general metabolism
2. abnormalities in the shape and size of chloroplast.
Deficiency symptoms of Sulphur :
1. Deficiency symptoms first appear in young leaves.
2. They become reduced, chlorotic followed by anthocyanin pigmentation in certain species.
3. Root system becomes extensive and stems become hard and woody.
Deficiency symptoms of Potassiam :
1. Deficiency symptoms are first observed on the older, lower leaves. Spots of dead tissue on older leaves are seen.
2. Potassium deficiency in cereal crops develop weak stalk. These plants easily bent to the ground by wind or rain.
Deficiency symptoms of Calcium :
1. Calcium deficiency brings about decomposition of root epidermis, roots become mucous, the growing zone and lateral roots rapidly die off.
2. Its deficiency terminates growth of meristematic regions.
3. Margins of younger leaves show chlorosis which become nacrotic.
4. Twig or stalk just below the tip and seed head is often unable to stand erect.
Deficiency symptoms of Magnesium :
1. Extensive interveinal chlorosis of the leaves resulting in defoliation;
2. Yellowing of the leaves start from basal to younger ones;
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?
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.
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.
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.