Plus One Botany Notes Chapter 8 Mineral Nutrition is part of Plus One Botany Notes. Here we have given Kerala Plus One Botany Notes Chapter 8 Mineral Nutrition.
|Text Book||NCERT Based|
|Chapter Name||Mineral Nutrition|
|Category||Plus One Kerala|
Kerala Plus One Botany Notes Chapter 8 Mineral Nutrition
All living organisms require macromolecules, such as carbohydrates, proteins and fats, and water and minerals for their growth and development, Minerals are provide nourishment to the living organisms or work as a raw material for body building and maintaining its normal functions are termed as mineral nutrients and the mode of taking all required nutrients is called mineral nutrition.
Methods to study the mineral requirements of plants
- In 1860, Julius von Sachs, demonstrated, for the first time, that plants could be grown to maturity in a defined nutrient solution in complete absence of soil.
- This technique of growing plants in a nutrient solution is known as hydroponics.
- Hydroponics has been successfully employed as a technique for the commercial production of vegetables such as tomato, seedless cucumber and lettuce.
- Bent tube is used for aeration. The nutrient solution flows down due to gravity and returns to the reservoir of the hydroponic setup. In this way, roots are batched in aerated nutrient solution continously.
- By this method, essential elements were identified and their deficiency symptoms discovered.
Essential Mineral nutrients
Essential elements are those which have structural or physiological role and without which plants are unable to complete their life cycle. Some plant species accumulate selenium, some others gold, while some plants growing near nuclear test sites take up radioactive strontium.There are techniques that are able to detect the minerals even at a very low concentration.
Criteria for essentiality
- The element must be absolutely necessary for supporting normal growth and reproduction. In the absence of the element the plants do not complete their life cycle or set the
- The requirement of the element must be specific and not replaceable by another element. In other words, deficiency of any one element cannot be met by supplying some other element.
- The element must be directly involved in the metabolism of the plant.
Classification of Essential mineral elements
Based upon the above criteria only a few elements have been found to be absolutely essential for plant growth and metabolism. These elements are further divided into two broad categories based on their quantitative requirements.
They are generally present in plant tissues in large amounts, e.g., carbon, hydrogen, oxygen, nitrogen, phosphorous, sulphur, potassium, calcium and magnesium. Of these, carbon, hydrogen and oxygen are mainly obtained from CO2 and H2O while the others are absorbed from the soil as mineral nutrition.
They are also called trace elements, are needed in very small amounts,
e.g., iron, manganese, copper, molybdenum, zinc, boron, chlorine and nickel.
Essential elements can also be grouped into four broad categories on the basis of their diverse functions. These categories are,
- As the constituents of biomoiecules.
They also known as structural elements of cells e.g., carbon, hydrogen, oxygen and nitrogen.
- As the energy related chemical compounds.
e.g., magnesium in chlorophyll and phosphorous in ATP.
- As a part of enzymes showing catalytic effect.
For example Mg2+ is an activator for both ribulose bisphosphate carboxylaseoxygenase and phosphoenol pyruvate carboxylase, both of which are critical enzymes in photosynthetic carbon fixation; Zn2+ is an activator of alcohol dehydrogenase and Mo of nitrogenase during nitrogen metabolism.
- As the elements altering osmotic potential.
e.g., Potassium plays an important role in the opening and closing of stomata.
Role of Macro- and Micro-nutrients
Various forms and functions of mineral elements are given below,
|Nitrogen (N)||Processes like protein synthesis, role of nucleic acids and chlorophyll synthesis.|
|Constituent of cell membranes, certain proteins, all nucleic acids and nucleotides, required for all phosphorylation reactions.|
|Maintain an anion-cation balance in cells and is involved in protein synthesis, opening and closing of stomata.|
|Calcium (Ca)||It is used in the synthesis of cell wall, also needed during the formation of mitotic spindle.|
|Constituent of the ring structure of chlorophyll and helps to maintain the ribosome structure|
|Sulphur (S)||Constituent of several coenzymes, vitamins (thiamine, biotin, Coenzyme A) and ferredoxin.|
|Iron (Fe)||Activates catalase enzyme, It is an important constituent of proteins involved in the transfer of electrons like ferredoxin and cytochromes.|
|It activates many enzymes involved in photosynthesis, respiration and nitrogen metabolism.|
|Zinc (Zn)||It activates various enzymes, especially carboxylases. It is also needed in the synthesis of auxin.|
|Copper (Cu)||It is essential for the overall metabolism in plants. Like iron, it is associated with certain enzymes involved in redox reactions.|
|Boron (B)||For uptake and utilisation of Ca, membrane functioning, pollen germination, cell elongation, cell differentiation and carbohydrate translocation.|
|It is a component of several enzymes, including nitrogenase and nitrate reductase both of which participate in nitrogen metabolism.|
|Chlorine (Cl)||It helps in determining the solute concentration and the anioncation balance in cells. It is essential for the water-splitting reaction in photosynthesis.|
Deficiency symptoms of essential elements
In the absence of any particular element, plants show certain morphological changes. These morphological changes are indicative of certain element deficiencies and are called deficiency symptoms. The deficiency symptoms vary from element to element and they disappear when the deficient mineral nutrient is provided to the plant.
The parts of the plants that show the deficiency symptoms also depend on the mobility of the element in the plant. Accordingly these can be divided as,
1. Mobile elements.
When the element are actively mobile within the plants, the symptoms tend to to appear first in the older leaves and tissues. It is because the elements get mobilised from senescing regions to young tissues.
2. Immobile elements.
The deficiency symptoms tend to appear first in the young tissues whenever the elements are relatively immobile and are not transported out of the mature organs.
Various kinds of deficiency symptoms shown by the plants are given below,
- Inhibition of cell division
- Delay flowering
- Stunted plant growth
- Premature fall of leaves and buds
Toxicity of micronutrients
The requirement of micronutrients is always in low amounts while their moderate decrease causes the deficiency symptoms and a moderate increase causes toxicity. Toxicity levels for any element also vary for different plants. Many a times, excess of an element may inhibit the uptake of another element. In other words, there is a narrow range of concentration at which the elements are optimum.
Mechanism of absorption of elements
Mineral absorption by plants is done by two different phases.
i. Initial phase (Passive transport).
It is the pathway by which water or ions present in the free space or outer space of cells are uptaken by roots of plants by taking apoplast pathway.
ii. Metabolic phase (Active transport).
It is the pathway which is dependent on metabolic energy in the form of ATP for the uptake of mineral ions by the roots into the inner spaces i.e., symplast pathway.
Translocation of solutes.
Mineral salts are translocated through xylem along with the ascending stream of water, which is pulled up through the plant by transpirational pull.
Soil as reservoir of essential elements
The soil enrich with dissolved ions and inorganic salts. Since they are derived from the rock minerals, their role in plant nutrition is referred to as mineral nutrition. Soil not only supplies minerals but also harbours nitrogenfixing bacteria, other microbes, holds water, supplies air to the roots and acts as a matrix that stabilises the plant. Since deficiency of essential minerals affect the crop-yield, there is often a need for supplying them through fertilisers. Both macro-nutrients and micronutrients form components of fertilisers and are applied as per need.
Metabolism of nitrogen .
i. Nitrogen Cycle
- Lightning and ultraviolet radiation provide enough energy to convert nitrogen to nitrogen oxides. Industrial combustions, forest fires, automobile exhausts and power-generating stations are also sources of atmospheric nitrogen oxides.
- Decomposition of organic nitrogen of dead plants and animals into ammonia is called
It is converted into nitrate by soil bacteria in the following steps,
2NH3 + 3O2 → +2NO–2 + 2H+ + 2H2O
2 NO–2 + O2 → 2 NO–3
- The nitrite is further oxidised to nitrate with the help of the bacterium Nitrobacter. These steps are called nitrification. These nitrifying bacteria are chemoautotrophs.
Biological nitrogen fixation
- Reduction of nitrogen to ammonia by living organisms is called biological nitrogen fixation.
The enzyme, nitrogenase which is capable of nitrogen reduction is present exclusively in prokaryotes. Such microbes are called N2– fixers
- The nitrogen-fixing microbes could be free- living or symbiotic.
- The free living bacteria can also further divided as free living aerobic and free living anaerobic.
Symbiotic biological nitrogen fixation
The most prominent types of symbiotic biological nitrogen fixing association is the legume- bacteria relationship. The most common association on roots is as nodules. These nodules are small outgrowths on the roots.
Nodule formation involves a sequence of multiple interactions between Rhizobium and roots of the host plant.
- Rhizobium multiply and colonize itself to the surrounding of the roots of host plant where it gets physically attached to the epidermal root hair.
- After attachment, the root hair gets curled up at the tip due to which bacteria invade the root hair.
- The enzymes from the bacteria degrade the parts of root hair cell wall which produces a thread-like structure called infection thread.
- The bacteria invade the infection thread and reaches upto the inner cortex of the root. Which stimulate the initiation of formation of nodule. A mature nodule is complete with vascular tissues continuous with those of the root.
N2 + 8e– + 8H+ + 16 ATP →2NH3 + H2 + 16 ADP + 16 Pi
Steps of conversion of atmospheric nitrogen to ammonia by nitrogenase enzyme complex found in nitrogen-fixing bacteria is given below schematically,
At physiological pH, the ammonia is protonated to form NH4+ (ammonium) ion. While most of the plants can assimilate nitrate as well as ammonium ions, the latter is quite toxic to plants and hence cannot accumulate in them.There are two main ways in which NH4+ used to synthesise amino acids in plants.
i. Reductive amination.
In these processes, ammonia reacts with a-ketoglutaric acid and forms glutamic acid as indicated in the equation given below.
It involves the transfer of amino group from one amino acid to the keto group of a keto acid. Glutamic acid is the main amino acid from which the transfer of NH2, the amino group takes place and other amino acids are formed through transamination. The enzyme transaminase catalyses all such reactions.
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