Biology

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Critical Concentration and Toxicity of Minerals

Critical Concentration

To increase the productivity and also to avoid mineral toxicity knowledge of critical concentration is essential. Mineral nutrients lesser than critical concentration cause deficiency symptoms. Increase of mineral nutrients more than the normal concentration causes toxicity. A concentration, at which 10% of the dry weight of tissue is reduced, is considered as toxic. Figure 12.2 explains about Critical Concentration.

Mineral Toxicity

a. Manganese Toxicity

Increased Concentration of Manganese will prevent the uptake of Fe and Mg, prevent translocation of Ca to the shoot apex and cause their deficiency. The symptoms of manganese toxicity are appearance of brown spots surrounded by chlorotic veins.

b. Aluminium Toxicity

Aluminium toxicity causes precipitation of nucleic acid, inhibition of ATPase, inhibition of cell division and binding of plasma membrane with Calmodulin. For theories regarding, translocation of minerals please refer Chapter – 11.

Critical concentration. (Science: chemistry) The minimum concentration of units needed before a biological polymer will form. Examples of biopolymers are microtubules from tubulin units, polypeptides from amino acid units, polysaccharides from simple Sugar units, etc.

The term mineral toxicity refers to a condition during which the concentration within the body of anybody of the minerals necessary for all times is abnormally high, and which has an adverse effect on health.

Critical level or concentration is a term that is common in both soil and plant analysis. It is usually defined in plant analysis as the level that results in 90% of maximum yield or growth, which is also a reasonable division of the zones of adequacy and deficiency in the figure below.

These include iron, manganese, copper, molybdenum, zinc, boron, chlorine and nickel. Toxic Elements Any mineral ion concentration in tissues, that reduces the dry weight of tissues by about 10% is considered toxic. For example, Mn inhibit the absorption of other elements.

As a group, minerals are one of the four groups of essential nutrients, the others of which are vitamins, essential fatty acids, and essential amino acids. The five major minerals in the human body are calcium, phosphorus, potassium, sodium, and magnesium.

Critical nutrient range is defined as: that range of nutrient concentration above which we are reasonably confident the crop is amply supplied and below which we are reasonably confident the crop is deficient.

Soil pH affects nutrient availability by changing the form of the nutrient in the soil. Adjusting soil pH to a recommended value can increase the availability of important nutrients. Low pH reduces the availability of the macro- and secondary nutrients, while high pH reduces the availability of most micronutrients.

These symptoms include cardiac arrhythmias, headache, nausea and vomiting, and in severe cases, seizures. Calcium and phosphate: Calcium and phosphate are closely related nutrients.

Critical Concentration is the term which is used to define the concentration of essential elements below which the growth of plant is Retarded or Reduced. Also, if the concentration of essential elements rise above the critical concentrations it leads to toxicity.

Calcium is required by meristematic and differentiating tissues. During cell division it is used in the synthesis of cell wall, particularly as calcium pectate in the middle lamella. It is also needed during the formation of mitotic spindle. It accumulates in older leaves. The criteria of essentiality were stated by Arnon and Stout.

The three criteria of essentiality of an element are:

1. Deficiency of the given element must cause some specific deficiency symptom so that the vegetative and reproductive stages of the life cycle of plant remain imcomplete.
2. Such 8 deficiency symptom can be prevented or corrected only by supplying this element.

The element must be critical for the growth and development of the plant. The plant can not complete its life cycle or produce seeds in the absence of the element. The requirement for the element must be specific and not replaceable by another element.

The beneficial elements are not deemed essential for all crops but may be vital for particular plant taxa. The distinction between beneficial and essential is often difficult in the case of some trace elements. These elements are not critical for all plants but may improve plant growth and yield.

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Deficiency Diseases and Symptoms

The following table (Table 12.2) gives you an idea about Minerals and their Deficiency symptoms:

Signs and symptoms of vitamin deficiency anemia include:

• Fatigue
• Shortness of Breath
• Dizziness
• Pale or yellowish Skin
• Irregular Heartbeats
• Weight Loss
• Numbness or tingling in your hands and feet
• Muscle Weakness

7 Nutrient Deficiencies:

That Are Incredibly Common

• Iron deficiency. Iron is an essential mineral
• Iodine Deficiency
• Vitamin D Deficiency
• Vitamin B12 Deficiency
• Calcium Deficiency
• Vitamin A Deficiency
• Magnesium Deficiency

Any currently treated or untreated nutrient deficiency or disease. These include, but are not limited to, Protein Energy Malnutrition, Scurvy, Rickets, Beriberi, Hypocalcemia, Osteomalacia, Vitamin K Deficiency, Pellagra, Xerophthalmia, and Iron Deficiency.

Nutritional Deficiencies can lead to conditions such as anemia, scurvy, rickets.

• Calcium
• Magnesium
• Omega-3 fatty acid
• Folate
• Potassium
• Vitamin A
• Vitamin E
• Copper

Copper deficiency is more common among people with untreated celiac disease than the general population. Stopping behaviors that contribute to the deficiency, such as unhealthy eating, smoking, and heavy alcohol use, can help prevent vitamin deficiency anemia. Eating a healthy diet can lower your risk of developing the condition. Some people take a daily vitamin supplement to help prevent the condition.

These deficiencies can result in many disorders including anemia and goitre. Examples of mineral deficiency include, zinc deficiency, iron deficiency, and magnesium deficiency.

A deficiency disease can be defined as a disease which is caused by the lack of essential nutrients or dietary elements such as vitamins and minerals in the human body. Deficiency disease examples: Vitamin B1 deficiency causes beriberi, lack of iron in the body can lead to anaemia.

There are four main types of disease: infectious diseases, deficiency diseases, hereditary diseases (including both genetic diseases and non-genetic hereditary diseases), and physiological diseases. Diseases can also be classified in other ways, such as communicable versus non-communicable diseases.

Vitamin and nutrition blood tests can detect gluten, mineral, iron, calcium and other deficiencies, telling you which vitamins you lack and which you are getting enough of through natural sources.

What are the causes of zinc deficiency? A poor diet can cause zinc deficiency. So it is more common in malnourished children and adults and in people who are unable to eat a normal diet due to circumstances or illness. Lots of zinc intake is from meat and seafood, so vegetarians may be more prone to deficiency.

There is a very simple and efficient test for zinc deficiency. For an adult, mix fifty mg of zinc sulphate in a half a glass of water. If it tastes sweet, pleasant or like water, then your body needs it. If it has a strong metallic or unpleasant taste, you are not zinc deficient.

Vitamin E deficiency may cause impaired reflexes and coordination, difficulty walking, and weak muscles. Premature infants with the deficiency may develop a serious form of anemia. The diagnosis is based on symptoms and results of a physical examination. Taking vitamin E supplements corrects the deficiency.

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Functions – Mode of Absorption and Deficiency Symptoms of Macronutrients

Micronutrients even though required in trace amounts are essential for the metabolism of plants. They play key roles in many plants. Example: Boron is essential for translocation of sugars, molybdenum is involved in nitrogen metabolism and zinc is needed for biosynthesis of auxin. Here, we will study about the role of micro nutrients, their functions, their mode of absorption, deficiency symptoms and deficiency diseases.

1. Iron (Fe):

Iron is required lesser than macronutrient and larger than micronutrients, hence, it can be placed in any one of the groups. Iron is an essential element for the synthesis of chlorophyll and carotenoids. It is the component of cytochrome, ferredoxin, flavoprotein, formation of chlorophyll, porphyrin, activation of catalase, peroxidase enzymes.

It is absorbed as ferrous (Fe²⁺) and ferric (Fe³⁺) ions. Absorbtion of Fe²⁺ ions are comparitively more than Fe³⁺ ions. Mostly fruit trees are sensitive to iron.

Deficiency:
Interveinal Chlorosis, formation of short and slender stalk and inhibition of chlorophyll formation.

2. Manganese (Mn):

Activator of carboxylases, oxidases, dehydrogenases and kinases, involved in splitting of water to liberate oxygen (photolysis). It is absorbed as manganous (Mn²⁺) ions.

Deficiency:
Interveinal chlorosis, grey spot on oats leaves and poor root system.

3. Copper (Cu):

Constituent of plastocyanin, component of phenolases, tyrosinase, enzymes involved in redox reactions, synthesis of ascorbic acid, maintains carbohydrate and nitrogen balance, part of oxidase and cytochrome oxidase. It is absorbed as cupric (Cu²⁺) ions.

Deficiency:
Die back of citrus, Reclamation disease of cereals and legumes, chlorosis, necrosis and Exanthema in Citrus.

4. Zinc (Zn):

Essential for the synthesis of Indole acetic acid (Auxin), activator of carboxylases, alcohol dehydrogenase, lactic dehydrogenase, glutamic acid dehydrogenase, carboxy peptidases and tryptophan synthetase. It is absorbed as Zn²⁺ ions.

Deficiency:
Little leaf and mottle leaf due to deficiency of auxin, Inter veinal chlorosis, stunted growth, necrosis and Khaira disease of rice.

5. Boron (B):

Translocation of carbohydrates, uptake and utilisation of Ca⁺⁺, pollen germination, nitrogen metabolism, fat metabolism, cell elongation and differentiation. It is absorbed as (borate) BO^3- ions.

Deficiency:
Death of root and shoot tips, premature fall of flowers and fruits, brown heart of beet root, internal cork of apple and fruit cracks.

6. Molybdenum (Mo):

Component of nitrogenase, nitrate reductase, involved in nitrogen metabolism, and nitrogen fixation. It is absorbed as molybdate (Mo²⁺) ions.

Deficiency:
Chlorosis, necrosis, delayed flowering, retarded growth and whip tail disease of cauliflower.

7. Chlorine (Cl):

It is involved in Anion – Cation balance, cell division, photolysis of water. It is absorbed as Cl^– ions.

Deficiency:
Wilting of leaf tips.

8. Nickel (Ni):

Cofactor for enzyme urease and hydrogenase.

Deficiency:
Necrosis of leaf tips.

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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 balance by ion-exchange. It is absorbed as K⁺ ions.

Deficiency Symptoms:
Marginal chlorosis, necrosis, low cambial activity, loss of apical dominance, lodging in cereals and curled leaf margin.

4. Calcium (Ca):
It is involved in synthesis of calcium pectate in middle lamella, mitotic spindle formation, mitotic cell division, permeability of cell membrane, lipid metabolism, activation of phospholipase, ATPase, amylase and activator of adenyl kinase. It is absorbed as Ca²⁺ exchangeable ions.

Deficiency Symptoms:
Chlorosis, necrosis, stunted growth, premature fall of leaves and flowers, inhibit seed formation, Black heart of Celery, Hooked leaf tip in Sugar beet, Musa and Tomato.

5. Magnesium (Mg):
It is a constituent of chlorophyll, activator of enzymes of carbohydrate metabolism (RUBP Carboxylase and PEP Carboxylase) and involved in the synthesis of DNA and RNA. It is essential for binding of ribosomal sub units. It is absorbed as Mg²⁺ ions.

Deficiency Symptoms:
Inter veinal chlorosis, necrosis, anthocyanin (purple) formation and Sand drown of tobacco.

6. Sulphur (S):
Essential component of amino acids like cystine, cysteine and methionine, constituent of coenzyme A, Vitamins like biotin and thiamine, constituent of proteins and ferredoxin. plants utilise sulphur as sulphate (SO₄^–) ions.

Deficiency Symptoms:
Chlorosis, anthocyanin formation, stunted growth, rolling of leaf tip and reduced nodulation in legumes.

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Classification of Minerals

Classification of Minerals Based on Their Quantity Requirements

Essential elements are classified as Macro-nutrients, 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.

Minerals like Sodium, Silicon, Cobalt and Selenium are not included in the list 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).

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:-

• Actively mobile minerals and
• Relatively immobile minerals (Figure 12.1).

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.

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.

Classification of Minerals Based on their Functions

Structural Component Minerals:
Minerals like Carbon, Hydrogen, Oxygen and Nitrogen

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.

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.

Energy Components:
Magnesium (Mg) in chlorophyll and phosphorous (P) in ATP.