Mineral Nutrition

Essential elements are the elements required by any organism for it’s normal growth.These are of two types of essential elements Macronutrients (Present in large amounts like Calcium, Magnesium etc.) and Micronutrients (Present in small amounts like Iron,Zinc etc.).They perform the following functions like being a component of biomolecules, being a structural component of energy related chemical compounds and activation or inhibition of enzymes but do not change the chemistry of soil.

The amount or concentration of the essential elements like Calcium,Magnesium,Zinc and Iron etc. below which the plant growth is retarded is known as critical concentration of an essential element.

It is because, the immobile elements are first transported to the tip level of the plant and as Sulphur is an immobile element,which is required by young leaves, stem and root tips. So if the deficiency of Sulphur occurs it would lead to reduced growth, extensive root growth, hard and woody stem and chloriosis which is the yellowing of leaves due to lack of chlorophyll takes place.

Manganese is an essential micro nutrient required by the seeds and leaves of the plant.If large amount of Manganese is absorbed by the plant, toxicity takes place. Which causes deficiency of both Iron and Nitrogen.It is because toxicity leads to reduced uptake of Magnesium,Iron and Nitrogen from the soil.

Bacteria carrying out these steps are Chemoautotrophs and not photoautotrophs.

Nitrogenase is sensitive towards oxygen molecule, such that to protect nitrogenase Rhizobium nodules also has an oxygen molecule scavenger called as Leg-Heamoglobin. Hence it does not require oxygen for it’s functioning.

Plants need essential elements for their growth with either water or soil.As in the case of soil less culture of plants where all the essential nutrients are dissolved in water (hydroponics).The plant growth remains intact even without soil.

Silicon is present in soil in good amounts but it is taken up by the plants in the form of mono-silicic acid.An example of one such plant which accumulates silicon is Oryza Sativa (Asian Rice).

Mycorrhiza is a mutualistic association between the roots of higher plants and fungi.The organisms involved in this association benefit from each other as in:

A) Fungi get carbohydrates from the plant for its growth.

B) The fungi in turn acts as the extension of root hairs and helps in increased absorption of the mineral and nutrients from the soil.

Nitrogen fixation is the process in which the atmospheric nitrogen is converted to ammonia (NH₃) in the presence of an enzyme Nitrogenase.Nitrogen fixation is shown by prokaryotesand not by eukaryotes because Prokaryotes have the enzyme Nitrogenase required for nitrogen fixation whereas eukaryotes does not have this enzyme.

Carnivorous plants like Nepenthes and Venus fly trap grow in nitrogen deficient soil.Which causes them to have nitrogen deficiency.So,as to full fill their need of nitrogen these plants trap an insect in their cavity.This cavity has a digestive fluid which digests the insect and absorbs nitrogen from it.

A plant called ‘Cuscuta’ is a stem parasite. The plant does not have chlorophyll in it.Hence, cannot perform photosynthesis and derives nutrition from the host plant.

CUSCUTA

Insectivorous angiosperms are the plants that trap insects and feed on them to get nutrition. Utricularia (Bladderwort) is an insectivorous angiosperm.

URTICULARIA (BLADDERWORT)

Azotobacter is nitrogen fixing bacteria in cereal crops like maize.Which means it converts free nitrogen in the air to ammonia (NH3) or other related nitrogenous compounds.The farmer adds Azotobacter culture to soil before sowing maize to enhance nitrogen content in the soil.

Leghaemoglobin is a red coloured pigment present in the root nodules of a legume.It is also considered as oxygen molecule scavenger because it combines with the oxygen molecule and helps in it’s removal. Thus helping enzyme nitrogenase in nitrogen fixation,which only works in absence of molecular oxygen.

Nepenthes, Utricularia and Drosera are all insectivorous angiosperms or Carnivorous plants.These plants trap insects and feed on them to get nutrition.

Plants with zinc deficiency show reduced biosynthesis of Auxin (IAA).Auxins are the hormones present in the stem tip and are involved in cell elongation.

Yellowish edges appear in leaves deficient in Nitrogen,Magnesium,Potassium and iron.

Carbon is the macronutrient which is a component of all organic compounds but is not obtained from soil.

Nitrogen fixing prokaryotes are of two types:

1. Nonsymbiotic nitrogen fixing prokaryote: Azotobacter,Beijernickia etc.

2. Symbiotic nitrogen fixing prokaryote:

Rhodospirilium and Clostridium etc.

Rice fields are submerged in water. The bacteria present in the water logged soil under anaerobic conditions produce Methane Gas (CH₄) which is a greenhouse gas.

:

1.Excess of Manganese (Mn) in the soil competes with Ca,Mg and Fe for uptake leading to their deficiency in the plant.

2.Manganese inhibits the translocation of calcium to the root apex hence causing it’s deficiency.

3.Manganese competes with Magnesium to bind with enzymes hence causing it’s deficiency.

Sulphur is present in plants in the form of Sulphate.It is important for plants because:

1. It is important for the formation of Chlorophyll.

2. It is the main constituent of various coenzymes.

3. It is the main constituent of various Vitamins like Thiamine,Coenzyme A and Biotin etc.

4. It is involved in the nodulation of legumes.

5. It is important for the structure of proteins.

Sulphur is present in two Amino acids :

1. Cysteine

2. Methionine

Pseudomonas and Thiobacillus are involved in the process of denitrification during the nitrogen cycle.During denitrification the nitrate present in the soil is converted to free nitrogen thus contributing to presence of nitrogen in the air.

a) The technique shown in the figure is Hydroponics or Soil less culture of a plant.In this technique the plants are grown in mineral nutrient solution instead of soil.

b) Tomato, Lettuce,Marijuana,Pepper and Cucumber.

c) Aerating tube:A bent tube used for proper aeration of the medium for growth of roots.

Feeding funnel:It is used for feeding nutrients and water to the medium.

1.Nitrogenase is the crucial enzyme found in root nodules for N₂ fixation it converts the free nitrogen in the air to Ammonia or other nitrogenous compounds.

2.Yes,it requires a special pink coloured pigment for its functioning called Leg Haemoglobin, present in the root nodules of a legume.It is also considered as oxygen molecule scavenger because it combines with the oxygen molecule and helps in it’s removal. Thus helping enzyme nitrogenase in nitrogen fixation, which only works in absence of molecular oxygen.

These values can be found out using Hydroponics.

Below the critical concentration the elements become deficient of an element and starts showing signs and symptoms of it’s deficiency.

Carnivorous plants exhibit nutritional adaptation because they have green leaves which shows they are Autotrophic but they grow in nitrogen deficient soil.So, to meet the nitrogen need these plants feed on insects to fulfil their nutritional requirement.

Example:In case of Pitcher Plant it is assumed that during the course of evolution the leaf folded inwards to form the inside of the pitcher .Now, this plant grows in nitrogen deficient soil and traps insects.These insects are digested inside the pitcher which has a digestive liquid and meet it’s nitrogen need.

A farmer adds/ supplies Na, Ca, Mg and Fe regularly to his field and yet he observes that the plants show deficiency of Ca, Mg and Fe because:

1. If the soil pH is not maintained, that is the soil is too Alkaline or too Acidic the plant is unable to take up the nutrients from the soil.Example: Too alkaline pH can lead to Iron deficiency.

Preventive Measure: Maintaining the pH and use of good quality fertilizers

2. Manganese Toxicity:Excess of Manganese (Mn) in the soil competes with Ca,Mg and Fe for uptake leading to their deficiency in the plant.

Preventive Measure: Excess Manganese should not be used.

a) If it is observed that deficiency of a particular element showed its symptoms initially in older leaves and then in younger leaves than this indicates that the element is actively mobilized.It is because, the immobile elements are first transported to the tip level of the plant and mobile elements to the base.

b) Highly Mobile elements: Nitrogen and Magnesium

Relatively Immobile elements:Calcium and Boron

c) If it is observed that deficiency of a particular element showed its symptoms initially in older leaves and then in younger leaves than this indicates that the element is actively mobilized.This information is used by agriculturist and horticulturist to understand the deficiency of a particular element.For example Sulphur is an immobile element so it’s deficiency is seen in younger leaves first.

a) Yes, the property of nitrogen fixation in a plant – leguminous or non-leguminous can be artificially induced by genetic engineering.It involves the introduction of a specific genes in the plant to produce nitrogenase enzyme which is involved in nitrogen fixation.

b) Mycorrihiza and Pine trees show symbiotic relationship.In this type of relationship both the organisms benefit from each other.

c) Yes, It is necessary for a microbe to be in close association with a plant to provide mineral nutrition.The most common association is in the form of nodules.The nodules has all the necessary biochemicals such as enzymes .For example the rod shaped Rhizobium has such relationship with several legumes like sweet pea, lentils, garden pea etc.

Essential elements are the elements which are necessary for a plant to grow and reproduce.The deficiency of these elements cannot be replaced by any other.There are two types of essential elements which are:

A) Macro elements :These are present in large amounts like Calcium, Magnesium etc.

B) Micro Elements: Present in small amounts like Iron,Zinc etc.

Criteria of essentiality :The essentiality not only depends on the presence of an element in the plant but also on the following criteria:

1. If the plant is unable to grow and reproduce without the presence of an element.

2. The element is specific and cannot be replaced by any other element.

3. The element is directly involved in the metabolism process.

Classification of essential elements based on the function they perform is as follows:

1.Essential elements as components of energy related compounds

For example Magnesium in Chlorophyll and Phosphorus in ATP molecule.

2.Essential elements as components of Structural elements of cells

For example Hydrogen bonds are seen in secondary structure of proteins,Carbon and Oxygen in proteins,lipids,carbohydrates and nucleic acids.

3.Essential elements as Activator and Inhibitor of enzymes:

For example Magnesium (Mg²⁺) is an activator of both Ribulose Bisphosphate and Phosphoenol pyruvate enzyme which are involved in photosynthetic carbon fixation.

4.Essential elements which can alter osmotic pressure:

For example Potassium plays an important role in opening and closing of Stomata.

No, excess of nutrients should not be given because if we supply these nutrients inexcess following conditions might occur:

1. Toxicity: Excess of a nutrient which reduces the dry weight of a tissue by 10% leads to toxicity of an element.

2. Uptake inhibited:Sometimes excess of a nutrient leads to inhibition of uptake of another elements, leading to their deficiency.For example:Increased level of Manganese inhibits the uptake of Calcium,Iron etc.

The following events take place:

1. Rhizobium multiply and colonise arround the surrounding of the roots and get attached to the epidermal and root hair cells.

2. Now, the root hair cells curl and the bacteria enters the root hairs.

3. After entering the root hair an infection thread is formed.Which carries the bacteria to the cortex of the root.

4. In the cortex nodule formation starts taking place .

5. Here, the bacteria are released from the thread in the cells, which leads to differentiation of nitrogen fixing cells.

6. A vascular connection is established with the host for exchange of nutrients.

Leghaemoglobin is a red coloured pigment present in the root nodules of a legume.It is also considered as oxygen molecule scavenger because it combines with the oxygen molecule and helps in it’s removal. Thus helping enzyme nitrogenase in nitrogen fixation,which only works in absence of molecular

Nodule consists of all the biochemicals like enzyme nitrogenase and Leg Haemoglobin.The process of nitrogen fixation involves the conversion of free nitrogen in the air into Ammonia or other nitrogenous compounds in the presence of enzyme Nitrogenase.

The end product of the biochemical events is Ammonia (NH₃).

Fate of Ammonia:The Ammonia produced through nitrogen fixation is incorporated in the amino acids as amino group.At physiological pH NH₃ group is protonated to NH₄⁺ group .

The two events by which NH₄⁺ group is incorporated into amino acids are:

1. Reductive Amination:In this reaction alpha Ketoglutaric acid forms glutamate.In this reaction Ammonia reacts with a-ketoglutaric acid to form glutamate.

2. Transamination: In this reaction amino group (NH₂) transfers from one amino acid to another amino acid transaminase enzyme catalyses this reaction.

Hydroponics or Soil less culture of a plant is the technique in which the plants are grown in mineral nutrient solution instead of soil.Many plants are grown using this technique like tomato,lettuce,cucumber etc. but this type of culture requires regular addition of mineral and change of water which is quite a hectic schedule.Most of the crops are still grown on land because the soil does not need regular addition of mineral and change of water it is already present.Hence, it is a convenient method.