Metabolic Utilization of Mineral ions & their deficiency Symptoms

CHAPTER: 9 (B)

Metabolic Utilization of Mineral ions & their deficiency Symptoms

(Mineral Nutrients & its Deficiency)

Utilization of Minerals Ions &Their Deficiency:

•      The process including the absorption and utilization of various mineral ions by plants for their growth and development is called mineral nutrition.

•      80 – 90 % of tissue is composed of water. The part of the tissue left behind is called the dry matter and typically it is about 10 -20 % of the original weight. The dry matter mainly consists of organic compounds. Its 80 % consists of plant cell walls, primarily cellulose and related carbohydrates.

•      This can be eliminated in the form of gases on combustion at 600⁰ C. The residue now left is ash which vary in different plant tissues from about 1- 0.15 % of the dry weight.

•       A careful analysis of the ash shows that it contains almost all of the chemical  elements present in the soil surrounding plant.

•      All these elements are not essential for the plant . Only 16 elements have been so far considered to be essential for the growth.

Criteria of essentiality of an element:-

Ø  Arnon and Stout 1939 suggested certain criteria that an element must fulfill in order to be classified as essential. These criteria are.

1. An element is essential if in its absence, the plant can not complete its life cycle.
2. An element is essential if it forms a part of any molecule or a constituent of plant that in itself is essential for the plant e.g. Nitrogen in protein. Magnesium in chlorophyll. Iron in cytochrome.
3. The element must act directly inside the plant or not enhance or suppress the availability of some other element.

Ø  From a practical point of view an element is considered essential if plants show deficiency symptoms when they are raised without that element in the medium, the symptom is recovered only by injecting the same deficient element.

Essential Elements (nutrients):

•      Elements (nutrients) which are required by the plants for their normal growth & development & which are not replaceable in their function by any other nutrients are referred to as essential elements. Examples: C, N, Mg etc.

Nonessential Elements (nutrients):

•      Nonessential elements are those nutrients that can be made by plants itself and can be replaceable in their function by other alternatives. Examples: Serine, Tyrosine, Phytochemical etc.

Ø  Sixteen elements have so far been found to fulfill the criteria of essentiality suggested by Arnon and Stout in 1939.

Ø  Sachs and Knop have divided these sixteen elements into two categories based on the quantity in which they are required by the plant.

1. Macroelements or Major elements or Macronutrients:- These elements are required by the plants in their large quantities i.e. 1 – 10 mg./ gm of dry weight. The elements are. C, H, O, N, S, P, Mg, K, Ca.  Total = 09

2. Micro elements or Micronutrients or Trace elements:- These elements are required by the plants in their lesser quantities i.e. 0.1 mg / gm of dry weight. These elements are Fe, Mn, Bo, Cu, Zn, Mo, Cl. Total = 07

Ø  Scientists have added a few more elements to the list of sixteen are  essential for certain group of plants.

Ø   e.g. Vanadium(Va), Silicon(Si), and Iodine(I) are essential for certain algae. Almunium(Al) is essential for some ferns. Selenium(Si) is essential for weeds.

Sources of essential elements:-

Ø  Depending upon the source of an element for the plant the elements have been divided into:

1. Mineral elements:-

•      These are the elements which the plants get from the soil e.g. S, P, Mg, K, Ca, Fe, Mn, Bo, Cu, Zn, Mo, Cl, N.

2. Non mineral elements:-

•      These are the elements which plant gets from the water and air e.g. C, H, O. 

•      Carbon in the form of Co₂ from air. Hydrogen in the form of water from the soil and Oxygen from the air.

•      Nitrogen is included in both the categories mineral and non mineral element because its source is both atmosphere and soil.

Role and deficiency symptoms of Macro elements:

1. Carbon, Hydrogen, and Oxygen:-

•      They are absorbed in the form of Co₂ and Water.

•      Co₂ is mostly obtained from air while water is obtained from the soil.

•      The three elements enter the composition of all types of organic compounds like carbohydrates, organic acids, fats, proteins, amino acids, enzymes, hormones, etc.

Role:

•      In short they build up the protoplasm. 

•      Maintain the pH Value. pH value influences the majority of reactions going on in the cells. 

•      In respiration oxidation of organic compounds involves the transfer of hydrogen from them to certain acceptor substances.

•       There is an exchange of H⁺ ions with cations during salt absorption.

Deficiency symptoms:

•      Deficiency of either Co₂ or water cause retardation of growth.

•      Respiration and oxidation mechanism will be stopped without oxygen

2. Nitrogen:-

•      The available forms of the Nitrogen in the soil  are No^-₃ and NH⁺₄ ions .

Role:-

•      Nitrogen is the mineral element that plants require in greatest amount. It is a constituent of important organic compounds like. Amino acids, Proteins, Nucleic acids, Chlorophyll, Hormones, Vitamins, ATP, NADP and NADPH coenzymes

Deficiency symptoms:

1. Poor growth of the plant.

2. The young leaves remain small and the older leaves fall off prematurely.

3. Chlorosis of leaves especially in the older leaves near the base of the plant.

4. Under severe conditions necrosis of the leaves occurs.

5. In cereals there is poor tillering, reduction in number of ears and number of grains per ear.

6. Flower formation is either suppressed or a few flowers are formed, fruits and seeds formed are small and less viable. Potato produces fewer tubers. 

7. When nitrogen deficiency develops slowly plants may be markedly slender and often woody stems.

8. Branching restricted.

3. Phosphorus:-

•      The major phosphorus containing ions in soil solution are monovalent (H₂PO₄^-), bivalent (HPo₄^2-), Trivalent(Po₄^3-).

•       Monovalent is present in acidic soils.

•      Bivalent is present in neutral soils.

•      Trivalent phosphate is present in alkaline soils.

Role:-

•      Phosphorus is the constituent of nucleoprotein, ATP, NADP, phospholipids .

•      Another important phosphorus containing compound is phytin found in seeds.

•      It is regarded as the phosphate reserve.

•      During seed germination it is mobilized and converted into other phosphate forms that are needed in the metabolism of young plants.

Deficiency symptoms:

1. Stunted growth.
2. In cereals there is poor tillering, reduction in number of ears and number of grains per ear.
3. Older leaves become darkish green in colour, contain small necrotic spots (dead tissue).
4. Stems of annual plants become reddish in colour due to formation of anthocyanin pigments.
5. Vascular tissues are poorly developed.
6. Death of older leaves.
7. Delay in maturation of plant
8. Production of slender (bur not woody) stems.
9. Some species produce excess anthocyanins giving the leaves a slight purple colouration but not associated with chlorosis.
10. Plants are unable to absorb and accumulate salts.

4. Potassium:- It is absorbed as k⁺ ions at high rates by the plants.

Role:-

1. It is necessary for meristematic growth.

2. It is involved in maintaining the water status of the plants by maintaining cell turgor.

3. It plays important role in opening and closing of stomata.

4. It is involved in the translocation of photosynthetates.

5. It is the activator of enzymes like: Diastase, Catalase, Invertase.

Deficiency symptoms:

1. Reduced growth rate.

2. First chlorosis and then necrosis on the margins and tips of older leaves.

3. Decrease in turgor.

4. Leaf wilting and abscission.

5. Roots become susceptible to rotting fungi in corn and the plant easily bends to ground (Lodging).

6. Stem becomes slender and weak with abnormally short internodes.

8. In absence of K⁺ other ions present exert toxic effects.

5. Sulphur:-

•       It is present in the soil in inorganic and organic form. The inorganic forms of sulphur in soil consists mainly of So₄^2-. The organic sulphur of the soil is made available to plants by microbial activity and So₄^2- is produced.

Role:

1. It is the constituent of most important compounds like amino acids (Cysteine and Methionine) Vitamins (Lipoic acid , Thiamin , Biotin , Coenzyme A) electron carrier Ferredoxin.

2. Sulphur forms disulphide bridges in proteins.

3. It forms an alkaloid sinigrin (Diallyl disulphide) which gives pungent odour to Onion and Garlic.

Deficiency Symptoms: 

1. Rate of plant growth is reduced. Shoot growth is more effected than root growth

2. Chlorotic symptoms occur first in the younger leaves rather then older leaves.

3. Premature leaf fall.

4. Reduction in nodule formation in legumes.  

5. Anthocyanin accumulation (responsible for purple coloration).

6. Calcium:- It is absorbed from the soil in the form of Ca ²⁺ ions.

Role:

1. It is required for cell division because it is used in mitotic spindle during cell division.

2. It is essential for the stabilization of newly synthesized membranes.

3. It is involved in the normal functioning of cell membranes.

4. It is used in the synthesis of new cell walls particularly the middle lamella that separates newly divided cells.

5. It is activator of enzymes like ATPase, Kinase, Phospholipase, α-amylase and succinate dehydrogenase.

6. It functions as secondary messenger for hormonal and environmental signals.

7. Development of thick cuticle in potamogeton (pond weed ) occurs when calcium is supplied in abundance.

8. It plays role in binding proteins and nucleic acids in chromosomes.

9. It controls metabolism of carbohydrates.

10. Calcium counteracts toxities of other elements eg. Oxalo-aceticacid is converted into calcium oxalate which is non toxic.

Deficiency symptoms:

1. Reduced meristematic activity because of necrosis of young meristematic regions.

2. Young leaves become deformed (rolling and curling).

3. The surface of apples is pitted with small brown necrotic spots called bitter pit disease. In tomato this disease is called blossom end rot.

4. Premature drop of flower and fruit by breaking of their stalks

5. Chlorosis starts from margins to middle or in the leaf area between the veins.

7. Magnesium:- Magnesium is absorbed in the form of divalent Mg ^2+.

Role:

1. Magnesium ions have a specific role in the activation of enzymes involved in respiration, photosynthesis, (rubisco) and the synthesis of DNA and RNA.

2. It is the part of ring structure of chlorophyll molecule.

3. Association of two sub units of ribosomes occurs in presence of Mg.

4. It is essential for the formation of carotenoids.

5. It is involved in the synthesis of magnesium pectate of middle lamella. 

Deficiency symptoms:

1. Chlorois between the leaf veins occurring first in the older leaves because of mobility of this element.

2. Premature leaf fall.

3. Chlorosis is followed by necrosis. Defoliation may also occur.

4. Phloem and pith becomes reduced or remain under developed.

5. There is reduced vegetative and reproductive growth.

6. In deficiency of Mg in tomato & fruits develop pale orange colour, reduced pulp and wooly flesh.

Role and deficiency symptoms of Micronutrients.

1. Iron:- Plants obtain iron in the form of ferric ions Fe³⁺

Role:

1. Iron has an important role as a component of enzymes involved in the transfer of electrons (redox reactions) such as cytochrome. In this role it is reversibly oxidized from Fe²⁺ to Fe³⁺ during electron transfer.

2. It is essential for the development of chloroplasts and maintenance of chlorophyll.

3. Essential for the formation of nucleic acids and synthesis of proteins.

Deficiency symptoms:

1. Chlorosis between the leaf veins occurring first in the younger leaves because iron cannot be readily mobilized from older leaves.

2. The veins may also become chlorotic and the whole leaf may become white.

3. In the leaves of cereals the deficiency is shown by alternate yellow and green stripes along the length of leaf.

4. Reduced growth because iron deficiency disturbs various plant activities like photosynthesis, Respiration, utilization of nitrate and protein synthesis.

2. Manganese:- It is absorbed in the form of Mn²⁺

Role:

1. Enzymes like Decarboxylases, dehydrogenases, involved in the tricarboxylic acid (Krebs) cycle are specially activated by manganese.
2. In the splitting of water to liberate oxygen during photosynthesis
3. In the formation of chlorophyll  & maintenance of lamellar structure of chloroplast.
4. It is essential for nitrogen metabolism
5. It affects absorption of Calcium and Potassium
6. It is involved in Auxin synthesis.

Deficiency symptoms:

1.         Interveinal chlorosis associated with the development of small necrotic spots.

2. In severe deficiency the leaves show premature fall or do not develop at all.

3. Both roots and stem apices may die back and will show stunted growth.

4. Flowers are often sterile.

5. Its deficiency causes disorganization of lamellar system of chloroplasts. 

3. Boron:- It is absorbed in the form of  borate  (Bo₃^3-).

Role:

 1. It plays role in cell elongation, nucleic acid synthesis, hormone responses and membrane  function.

2. It plays role in carbohydrate and auxin translocation
3. Pollen germination.                                                        
4. It is required for uptake and mobilization of calcium.
5. Maintenance of sugar and starch balance.
6. Pectin formation.
7. Production of root nodules in legumes.

Deficiency symptoms:

1. Death of root and shoot tip.                                             
2. Black necrosis of the young leaves and terminal buds.
3. Fruits, fleshy roots and tubers may exhibit necrosis or abnormalities related to the breakdown of internal tissues.
4. Absence of root nodules in leguminous plants.
5. Disturbance in pollen germination.                                   
6. Stunted growth.
7. Reduced level of pectin.
8. Accumulation of fat.
9. There is a shift from common path way of respiration to pentose phosphate path way.  

4. Copper:- It is absorbed as Cupric ions(Cu^2+).

Role:

1. It is the constituent of enzymes involved in redox reactions being reversibly oxidized from Cu⁺ to Cu²⁺ like Plastocyanin which is involved in electron transfer during the light reaction of photosynthesis.

 2. It enters in composition of enzyme rubisco which takes part in carbon dioxide assimilation. Tyrosinase which is required in the formation of chlorophyll.

3. It is connected with maintenance of carbohydrate/nitrogen balance of plant.

Deficiency symptoms:

1. Production of dark green leaves which may contain necrotic spots.

2. The leaves may also be twisted or malformed

3. Under extreme copper deficiency leaves may abscise prematurely.

4. Its deficiency causes two diseases (a).Exanthema:- In this disease tree bark shows deep slits from which gum exudes also called die back disease. (b). Reclamation disease:- Tips of leaves undergo chlorosis, hence it is also called leaf tip disease.

5. Stunted growth.

6. Fruits formed are fewer. They may show necrosis and skin splitting

7. Blackening of potato is also caused by shortage of copper.

5. Zinc:- Zinc is absorbed as Zinc ions (Zn²⁺).

Role:

1. It is a component of many enzymes like Carbonic anhydrase, alcohol dehydrogenase, lactic dehydrogenase, glutamic dehydrogenase, carboxypeptidase and alkaline phosphatase.

2. It is required for some processes in carbohydrate metabolism, RNA synthesis, Protein synthesis, and synthesis of auxin or its precursor.

3. It is required for activity of copper containing superoxide dismutase.

4. It is involved in chlorophyll synthesis in some plants.   

Deficiency symptoms:

1. Reduction in internodal growth as a result plants display a rosette habit of growth in which the leaves form a circular cluster radiating at or close to ground (called rosette disease). It may be due to loss of the capacity to produce sufficient amount of auxin.

2. Leaves may become intervenously chlorotic and then develop white necrotic spots called white bud. It may be due to zinc requirement for chlorophyll biosynthesis. 

3. Protein synthesis and protein levels are markedly lowered.

4. Seed and fruit formation is reduced

6. Molybdenum:- It is available in the soil solution as monovalent and divalent molybedates (HMoO_4,^- MoO₄^2-) exists as Mo⁴⁺ to Mo⁶⁺

Role:

1. It is a component of several enzymes including nitrogenase and nitrate reductase. Nitrogenase converts nitrogen gas to ammonia in nitrogen fixing organisms. Nitrate reductase catalyses the reaction of nitrate to nitrite.

2. It plays role in the synthesis of ascorbic acid.

3. It plays role in the hydrolysis of organic phosphates.

Deficiency symptoms:

1. Nitrogen deficiency in plants.

2. General chlorosis between veins.

3. Necrosis of older leaves.

4. Whip tail disease in crucifers, in which leaves twist and subsequently die.

5. Flower formation is prevented or fall prematurely.

7. Chlorine:- It is absorbed as Chloride anion (Cl ^–)

 Role:

1. It is required for the water splitting reaction of photosynthesis through which oxygen is produced.

2. It is required for cell division both in leaves and roots.

3. With Na ⁺ and K⁺ it helps in determining solute concentration and anion cation balance in cells.

4. It is required for normal production of fruits.

Deficiency symptoms:

1.Reduced growth and wilting of leaf tips      

2.Chlorosis and necrosis of the leaves, turn  bronze coloured.

3.Stunted roots thickened at the tips               

4. Reduced fruiting