Mineral nutrition

Mineral Nutrition for CBSE Grade 11

1. MINERAL NUTRITION

2. Subtopics

3. Introduction Living organism- Macromolecules (Carbohydrates, proteins & fat), water and minerals for growth and development. Def. - A mineral is a chemical element which naturally occurs as inorganic nutrients in the food and soil, and are essential for the proper functioning of the plant and animal body. Other than carbon, hydrogen, oxygen & sulphur- organic molecules

4. Methods to study Mineral requirements of Plants Julius von Sachs, German botanist in 1860- that plants could be grown to maturity in a defined nutrient solution in complete absence of soil- hydroponics. Method involves growing plants in purified water & specific mineral nutrient salts- nutrient solution is aerated for optimum growth Concentration required is determined- adding/removing mineral solution- identify essential elements & deficiency

5. Hydroponics- commercial production of vegetables such as tomato, seedless cucumber and lettuce

6. Criteria for Essentiality of minerals Minerals present in soil enters plant- roots Criteria for essentiality of mineral elements: 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 seeds. 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.

7. Based on quantitative requirement by plants: Macronutrients Micronutrients MACRONUTIENTS Large amounts in plant tissues ( in excess of 10 mmole Kg -1 of dry matter) Carbon, hydrogen, oxygen, nitrogen, phosphorous, sulphur, potassium, calcium and magnesium- CO 2 , H 2 O & soil MICRONUTRIENTS Trace elements, less than 1 mmole Kg -1 of dry matter iron, manganese, copper, molybdenum, zinc, boron, chlorine and nickel Higher plants- sodium, silicon, cobalt and selenium

8. Classification of Elements based on function Based on diverse function: Structural Elements : Components of biomolecules (Carbohydrates, proteins, lipids & nucleic acid). Eg . C, H, O & N Energy related chemical compounds : Provide energy to plants. Eg . Mg in chlorophyll & Phosphorus in ATP Elements activate & inhibit enzymes : Activates or inhibits enzymes during metabolism. Eg . Mg 2+ - activator of ribulose bisphosphate carboxylaseoxygenase & phosphoenol pyruvate carboxylase-photosynthetic carbon fixation; Zn 2+ - an activator of alcohol dehydrogenase & Mo of nitrogenase - nitrogen metabolism. Elements altering water potential : Alters osmotic potential of cell. Eg . K- opening and closing of Stomata; regulates water potential of cells

9. Toxicity of Micronutrients Micronutrients- low amounts Decrease- deficiency, moderate increase- toxicity Any mineral ion concentration in tissues that reduces the dry weight of tissues by about 10 per cent is considered toxic . Critical concentration- vary & toxicity level vary with different plants Excess micronutrients- Toxicity Eg . Manganese toxicity

10. Manganese Toxicity Brown spots around chlorotic veins MODE OF TOXICITY: Manganese competes with iron and magnesium for uptake Magnesium for binding with enzymes Inhibit calcium translocation in shoot apex. RESULT: Excess of manganese- Induce deficiencies of iron, magnesium and calcium.

11. Absorption of Elements Studies carried on cells/tissues/organs- occurs in 2 phase: First phase- Rapid uptake of ions- ‘free space/ outer space’- the apoplast ; passive; occurs through ion-channels, the trans-membrane proteins which functions as selective pores. Second phase- Ions are taken slowly- inner space- the symplast ; entry and exit of ions require metabolic energy Inward movement- Influx & Outer movement- Efflux Translocation of Solutes Occurs through- xylem along with the ascending stream of water, which is pulled up through the plant by transpirational pull. Xylem sap- mineral salts

12. Soil as reservoir of Essential elements Nutrients essential for growth & development- weathering & breakdown of rocks Enrich soil with dissolved ions & inorganic salts Since nutrients derived from rock minerals so their role- mineral nutrition Other function of soil- harbour nitrogen- fixing bacteria, microbes, holds water, supplies air to the roots & act as a matrix that stabilises the plant Deficiency of macro- nutrients (N, P, K, S, etc.) & micro- nutrients (Cu, Zn, Fe, Mn , etc.)- supplied through fertilizers as per need

13. Metabolism of Nitrogen Nitrogen- macronutrient; constituent of - amino acids, proteins, hormones, chlorophylls & vitamins Plant gets N through soil (limited) & from air (atmospheric N 2 ) Plants have to compete with microbes for limited nitrogen present in soil Metabolism of Nitrogen: Nitrogen Cycle Biological Nitrogen fixation

14. Nitrogen Cycle Def.- A continuous series of natural processes by which nitrogen passes successively from air to soil to organisms and back to air or soil involving principally nitrogen fixation, nitrification, decay, and denitrification The process of nitrogen cycle: Nitrogen fixation Ammonification Nitrification Denitrification

15. Nitrogen Fixation: The process of conversion of nitrogen (N 2 ) into ammonia (NH 3 ) Lightning, ultraviolet radiations converts free nitrogen to nitrogen oxides (NO, NO 2 , N 2 O); Industrial combustion, forest fires, automobile exhausts and power-generating stations- sources of atmospheric nitrogen oxides. Nitrogen oxides converts to Ammonia N 2 Nitrogen oxides NH 3 Ammonification: The process of decomposition of organic nitrogen of plants and animals into ammonia (NH 3 ) Ammonia volatilises and re-enters the atmosphere but most of it is converted into nitrate (NO 2 - )

16. Nitrification: Ammonia is oxidised to nitrite (NO 2 - ) by the bacteria Nitrosomonas / Nitrococcus . The nitrite is further oxidised to nitrate (NO 3 - ) with the help of the bacterium Nitrobacter . These nitrifying bacteria are chemoautotrophs . Nitrate- absorbed by plants & transported to leaves where nitrate reduce to form ammonia (NH 3 ) & forms amine group of amino acids Denitrification: Nitrate present in the soil reduce to nitrogen by the process of denitrification. Denitrification is carried by bacteria Pseudomonas and Thiobacillus .

17. Biological Nitrogen Fixation Reduction of nitrogen to ammonia by living organisms is called Biological Nitrogen Fixation (N 2 NH 3 ) Certain prokaryotes (bacteria) fixes nitrogen – enzyme nitrogenase & called N 2 fixers Nitrogen-fixing microbes can be classified as follows: Free living : Aerobic ( Azotobacter , Beijernickia ), Anaerobic ( Rhodospirillum ), Cyanobacteria ( Nostoc , Anabaena ), Bacillus . Symbiotic – with leguminous plants ( Rhizobium ), with non-leguminous plants ( Frankia ).

18. Symbiotic Nitrogen Fixation: Commonly seen in legume-bacteria relationship. Bacteria Rhizobium (rod- shaped) forms nodules at root in legumes Nodules- small outgrowths on roots, central portion of nodule is pink- leguminous haemoglobin or leg-haemoglobin Microbe, Frankia produces nitrogen-fixing nodules on the roots of non-leguminous plants (e.g., Alnus ). Rhizobium and Frankia are free living in soil, but as symbionts, can fix atmospheric nitrogen.

19. Nodule Formation: Interaction between Rhizobium & roots of host plants Step involved includes: Multiplication of Rhizobia & colonization of it around roots Attachment of bacteria to epidermal & root hair cells Root hair curls & bacteria invade root hair An infection thread is produced- carries bacteria to cortex Initiation of nodule formation in the cortex Release of bacteria from the thread into the cells which leads to the differentiation of specialised nitrogen fixing cells. The nodule thus formed, establishes a direct vascular connection with the host for exchange of nutrients.

20. Root nodule- contains necessary biochemical components such as the enzyme nitrogenase and leghaemoglobin . The enzyme nitrogenase is a Mo-Fe protein and catalyses the conversion of atmospheric nitrogen to ammonia

21. Nitogenase Enzyme: Highly sensitive to molecular oxygen, anaerobic condition Nodule- ensures enzyme is protected from oxygen due presence of leg- haemoglobin (oxygen scavenger) Rhizobium- live as aerobes under free living condition ( Nitogenase - not operational) but during nitrogen fixing- anaerobic (to protect nitrogenase ) For enzyme to catalyse reaction- 8 ATP for each NH 3 produced Energy required is obtained through respiration of host cells

22. Fate of Ammonia: Ammonia (toxic) once formed is protonated to form NH 4 + (ammonium) ion Nitrate assimilate in most plants Ammonia (NH 4 + ) used to synthesise amino acids in plants: Reductive amination- In these processes, ammonia reacts with α-ketoglutaric acid and forms glutamic acid Transamination Transfer of amino group from one amino acid to the keto group of a keto acid- Transaminase catalyses all such reactions. Eg - Asparagine  and glutamine - aspartic acid and glutamic acid (asparagine synthetase   and glutamine synthetase .)