Study Notes on Mineral and Nutrition

Study Notes on Mineral and Nutrition

  • Julius Von Sachs demonstrated that plants can be grown in a defined nutrient solution in complete absence of soil
  • This technique is known as hydroponics
  • In this method the nutrient elements were added or removed or given in varied concentration.
  • After this the mineral solution suitable for the plant growth was obtained.
  • This method helped in identification of different elements and their deficiency symptoms.
  • This technique is also used for commercial production of vegetables such as tomato, seedless cucumber and lettuce.

ESSENTIAL MINERAL ELEMENTS

  • More than 60 mineral elements out of 105 discovered are found in different plants.
  • Variety of elements are required for the growth of different kind of plants.
  • For instance some plant species accumulate selenium, some others gold, while some plants growing near nuclear test sites take up radioactive Strontium

CRITERIA FOR ESSENTIALITY

  • The element must be absolutely necessary for normal growth and reproduction.
  • In the absence of the element the plants could not complete their life cycle or set the seeds.
  • The element cannot be replaceable by another element.
  • This means 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.
  • Based on these criteria only a few elements have been found to be absolutely essential for plant growth and metabolism.
  • The essential elements are further divided into two broad categories based on their quantitative requirements.
  • Macronutrients and Micronutrients.
  • The macro nutrients are generally present in plant tissues in large amounts.
  • Carbon, hydrogen ,oxygen ,nitrogen, phosphorus, sulphur, potassium, calcium and magnesium are the macronutrients.
  • Carbon, hydrogen and oxygen are mainly obtained from CO2 and H2
  • The other elements are absorbed from the soil as mineral nutrition.
  • Micronutrients are also called as trace elements.
  • These are needed in very small amounts.
  • Iron , manganese , copper , molybdenum , zinc, boron, chlorine and nickel are the micronutrients.
  • There are 17 essential elements in total.
  • In addition to these there are some beneficial elements such as sodium silicon cobalt and selenium.
  • The beneficial elements are mostly required by the higher plants.
  • On the basis of their diverse functions can be grouped into four broad categories.
  • Carbon hydrogen oxygen and nitrogen are the elements as components of biomolecules.
  • Hence, these are the structural elements of cells.
  • The elements that are components of energy related chemical compounds in plants are magnesium in chlorophyll and phosphorus in ATP.
  • The essential elements that activate or inhibit enzymes are magnesium zinc and molybdenum.
  • Mg2+ is an activator of the critical enzymes in photosynthetic carbon fixation.
  • Zn2+ is an activator of alcohol dehydrogenase.
  • Molybdenum is the activator of nitrogen is during nitrogen metabolism.
  • There are some essential elements available dose can alter the osmotic potential of a cell.
  • Potassium plays an important role in the opening and closing of stomata.

ROLE OF MACRO AND MICRONUTRIENTS

  • Nitrogen – it is absorbed mainly as NO3–   or sometimes also taken up as NO2– or NH4– .
  • Nitrogen is particularly required by meristematic tissues and metabolically active cells.
  • It is one of the major constituents of proteins , nucleic acids, vitamins and hormones.
  • Phosphorus – absorbed by plants from soil in the form of phosphate ions.
  • Required for all phosphorylation reactions.
  • It is a constituent of cell membranes , certain proteins ,all nucleic acids and
  • Potassium – absorbed as potassium ion K+.
  • Required in large quantities in the meristematic tissues, buds, leaves and root tips.
  • Potassium helps –
    • To maintain an anion cation balance in cells
    • Involved in protein synthesis
    • Opening and closing of stomata
    • Activation of enzymes
    • Maintenance of the turgidity of cells
  • Calcium – absorbed from the soil in the form of calcium ions.
  • Required by the meristematic and differentiating tissues.
  • Used in the synthesis of cell wall during cell division.
  • Present as calcium pectate in middle lamella of the cell wall.
  • Also involved in the formation of mitotic spindle.
  • Also required for activation of certain enzymes.
  • Magnesium – absorbed by plants in the form of divalent magnesium.
  • It is a constituent of the ring structure of chlorophyll.
  • Magnesium helps :
    • Activation of the enzymes for respiration and photosynthesis
    • In the synthesis of DNA and RNA.
    • To maintain the ribosome structure.
  • Sulphur – absorbed in the form of sulphate.
  • Main constituent of several coenzymes vitamins and ferredoxin.
  • Present in two amino acids , cysteine and methionine.
  • Iron – obtained in the form of ferric ions.
  • It is a micronutrient and required in larger amounts.
  • Activates catalase enzyme.
  • Essential for the formation of chlorophyll.
  • It is an important constituent of proteins.
  • Involved in transfer of electrons like ferredoxin and cytochromes.
  • Manganese – absorb in the form of manganous ions.
  • Manganese helps :
    • In activation of many enzymes involved in photosynthesis respiration and nitrogen metabolism.
    • In the splitting of water to liberate oxygen during photosynthesis.
  • Zinc – obtained as zinc ions.
  • Activates the enzyme carboxylases.
  • Needed in the synthesis of auxin.
  • Copper – absorbed as cupric ions.
  • Associated with certain enzymes involved in redox reactions.
  • Essential for the overall metabolism in plants.
  • Boron – required for uptake and utilisation of calcium ions.
  • Required for membrane functioning pollen germination cell elongation , cell differentiation and carbohydrate translocation.
  • Chlorine – absorbed in the form of chloride anion.
  • Helps in determining the solute concentration.
  • Essential for water splitting reaction in photosynthesis.
  • This leads to oxygen evolution.

DEFICIENCY SYMPTOMS OF ESSENTIAL ELEMENTS.

  • The concentration of essential elements below which plant growth is retarded is termed as deficiency of the essential elements.
  • The element is present below the critical concentration.
  • In the absence of any particular element plants show certain morphological changes.
  • The changes are the symptoms of the deficiency of any certain element.
  • The symptoms vary from element to element.
  • After the deficient mineral nutrient is provided to the plant the symptom disappears.
  • But it may lead to the death of the plant if the deficiency continues.
  • The deficiency symptoms tend to appear first in the older tissues when the element is mobilized.
  • When the elements are relatively immobile the deficiency symptoms tend to appear first in the young tissues.
  • The deficiency symptoms could be :
    • Chlorosis
    • Necrosis
    • Stunted plant growth
    • Premature fall of leaves and buds.
    • Inhibition of cell division.
  • Chlorosis is the loss of chlorophyll leading to yellowing in leaves.
  • Deficiency nitrogen, potassium, magnesium, sulphur, iron, manganese, zinc and molybdenum causes chlorosis.
  • Necrosis is death of tissue.
  • It is due to deficiency of calcium, magnesium, copper and potassium.
  • Lower level of nitrogen, potassium, sulphur, molybdenum causes an inhibition of cell division.
  • Deficiency of any element can cause multiple symptoms.
  • Same symptoms may be caused by deficiency of more than one elements.
  • Different plants respond differently to the deficiency of the same element.

TOXICITY OF MICRONUTRIENTS.

  • Micronutrients are always required in lower amounts.
  • A moderate increase in micronutrients causes toxicity.
  • Micronutrients have a narrow range of concentration at which they are optimum.
  • The concentration at which the dry weight of the tissues are reduced by about 10% is considered as toxic.
  • The toxic concentration vary widely among different micronutrients.
  • The symptoms for the toxicity is difficult to identify.
  • Toxicity level of any element also vary for different plants.
  • Toxicity may result in the inhibition of the uptake of another element.
  • For example manganese inhibit calcium translocation in shoot apex.

MECHANISM OF ABSORPTION OF ELEMENTS.

  • The process of absorption can be studied in two main phases.
  • In the first phase and initial rapid uptake of Ions into the free space of cells i.e. apoplast takes place.
  • This is a passive uptake.
  • This movement usually occurs through Ion channels.
  • In the second phase the ions are taken in slowly into the inner space which is the simplast of the cells.
  • This requires expenditure of metabolic energy so this is an active process .
  • The inward movement of Ions into the cells is called influx.
  • The outer movement is called efflux.

TRANSLOCATION OF SOLUTES

  • Mineral salts are translocated through xylem.
  • This takes place along with the ascending stream of water.
  • The water stream is pulled up through the plant by transpirational pull.

SOIL AS RESERVOIR OF ESSENTIAL ELEMENTS

  • Majority of essential nutrients are available to the roots due to weathering and breakdown of rocks.
  • Due to this the soil is enriched with dissolved ions and inorganic salts.
  • Soil also harbours nitrogen fixing bacteria.
  • Soil also acts like a matrix that stabilized the plant.

METABOLISM OF NITROGEN

  • Nitrogen cycle :
  • The process of conversion of nitrogen into ammonia is termed as nitrogen cycle.
  • Lighting and ultraviolet radiation provide enough energy to convert nitrogen into nitrogen oxides.
  • Decomposition of organic nitrogen of dead plants and animals into ammonia is called ammonification.
  • Some of these ammonia renters the atmosphere but most of it is converted into nitrate by soil bacteria.
  • 2NH3 + 3O2 – 2NO2– + 2H+ + 2H20

2NO2– + O2 – 2NO3–

  • Ammonia is first oxidised to nitrate by the bacteria Nitrococcus.
  • Nitrite is an oxidised to nitrate with the help of bacteria Nitrobacter.

 

BIOLOGICAL NITROGEN FIXATION

  • Certain prokaryotic are capable of nitrogen fixation.
  • Nitrogen fixing microbes could be free living or symbiotic.
  • Free living nitrogen fixing aerobic microbes are Azotobacter.
  • Azospirillum forms associative relationship with
  • Conversion to ammonia from nitrogen molecule in presence of nitrogenase.

Study Notes on Mineral and Nutrition

  • The energy required for nitrogen fixation by the symbiotic microbes is obtained from the respiration of the host cells.
  • Microbes require 16 molecules of ATP to reduce one molecule of nitrogen.
  • Rhizobium colonies the host leguminous plant’s root system.
  • This causes the roots to form
  • The bacteria then begin to fix nitrogen required for the plant.