Chapter-12
Mineral Nutrition
- Points to Remember
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Autotroph : An organism that sytheaize its required nutrients (organic components) from simple and inorganic substance; Example - plants, blue, green algae (cyanobacteria)
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Heterotroph : An organism that cannot synthesise its own nutrients and depend on ohters. Example - Bacteria, protists, members of animaila.
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Chlorosis : Yellowing of leaves due to loss of chlorophyll.
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Nitrification : Conversion og ammonia (NH3) into nitrite and then to nitrate.
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Denitrification : A process of conversion of nitrate into nitrous oxide amd nitrogen gas (N2).
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Leg-hemoglobin ; pinkish pigment found in hte root nodules of legumes. It acts as oxygen scavengar and protects the nitrogenase enzyme from oxidation.
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Flux : The movementbof ions is called flux. Influx is inward movement of ions into the cells and wfflux is the outward movement of ions.
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Inhibitiin of cell dividision : Deficiency of N,K,S. and Mo.
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Necrosis : Death of tissues particularly leaf tissues due to deficiency of Ca, Mg, Cu, K.
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DelayedbFlowering : Due to deficiency of N, S, Mo.
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Mineral Nutrition : Soli-less culture of plants, where roots are immersed in nutrient solution (without soil) is called hydroponics. The result obtained from hydroponics may be used to detwrmine deficiency symptoms of essential elements.
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Active Transport : Absorption occuring at the expense of metabolic energy.
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Passive Transport : Absorption of minerals with concentration gradient by the process of diffuaion without the expense of metabolic energy.
Essential Elements
Criteria for essentiality :
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1. The element must be necessary for supporting normal growth and reproduction.
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2. Requirement must be specific and not replaceable by another element.
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3. The element must be directly involved in the metabolism of the plant.
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Critical Concentration : The Concentration of the essential element below which plant growth is retarted. The element is said to be deficient when present below the critical concentration.
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Deficiency symptoms : Chlorosis, necrosis, stunted growth, premature fall of leaves and buds inhibition of cell division.
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Toxicity of micronutrient : Any mineral ion concentration in tissues that reduces the dry weightbof tissuesbby 10% is considered toxic. Toxicity of one element may lead to deficiency of other element since the former may inhibit the uptakebof latter., e.g., Mn competes with Fe, Mg for uptake and also inhibits Ca as deficiency symptoms of Fe, Mg, and Ca.
Role of microbes in nitrogen cycle :
- Rhizobium, Azotobacter, Rhodospirillum; Fix atmospheric nitrogen.
- Nitrosomonas and/or Nirococcus : Conversion of ammonia to nitrite.
- Nitrobacter : Conversion of nitrite into nitate.
- Pseudomonas and Thiobacillus : Reduce into nitrogen.
Nitrogen Cycle
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Nitrogen fixatiin : The process of conversion of nitrogen (N2) into ammonia (NH3).
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Ammonification : The process of decomposition of organic nitrogen of plants and animals (proteins) into ammonia.
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Nitrification : The ammonia so formed may volatilise and re-enterbthe atmosphere, or somebof the ammonia may be converted first into nitrite and then into nitrate by soil bacteria.
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The Nitrate so formed can be easily absorbed by the plants amd transported to leaves. In leavea, nitrate is reduced to ammonia to form amino-acid, because nitrate cam not ised by plants as such.
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Denitrification : Process of reduction of tjr nitrate present in soli to nitrogen. It is carried out by bacteria liks Pseudomonas and Thiobacillus.
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Biological Nitorgen Fixation : Reduction of nitrogen to ammonia by living organism. Certain prokaryotes are able to fix nitrogen because of presence of 'nitrogenase' enzyme in them.
Nitrogen fixing microbes may be
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(a) Free living : (i) Aerobic -Azotobacter
(ii) Anaerobic - Rhodospirillum
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(b) Cyanobacteria - Nostoc, Anabaena
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(c) Symbiotic : (i) With leguminous planst - Rhizobium
(ii) With non-leguminous plants - Frankia
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Enzyme nitrogenase : The enzyme nitrogenase is Mo-Fe protein and catalysis the conversion of atmospheric nitrogen to ammonia (First stable product of nitrogen fixatiin)
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Leg-hemoglobin : A pink colour pigment, similar to hemoglobin of vertebratea and functions as an oxygen scavewnger and protects nitrogenase from oxygen.
Steps of nodule formation :
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(a) Rhizobium bacteria present in soil contact a susceptible root hair.
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(b) Infectiin of the root hair cause it to curve and deformed due to chemical secretion.
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(c) An infection thread is produced carrying the bacteria into the cortex of the root
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(d) The bacteria get modified into rod-shaped bacteria and cause inner and pericycle cells to divide plant produce cytikinin and auxin to stimulate cell division and enlarge to form nodules.
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(e) Divisuon and growth of cortical and pericycld cella lead to nodle formation.
Mechanisms of N2 fixation
- It require 4 components
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(a) A strong reducing agemt like FADH2, NADPH2
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(b) Nitrogenase enzyme
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(c) ATP (as energy service)
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(d) Nitrogen gas molecule (as substrate)
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N2 + 8e- + 16 ATP ---> 2NH3 + H3 + 16 ADP + 16Pi
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Fate of Ammonia : At physiological pH, the ammonia is protinated to firm NH4+, whixh is quitd toxie to plants and hence can not accumulate in them. It is used by plants in following ways--
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(a) Reductibe amination :- a- Ketoglutaric acid + NH4 + + NADP
glutamate
--------------> glutamate + H2O + NADP
Dehydrogenase
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(b) Tranasmination :- Transfer of amino group frim one amino acid to group of a keto acid to form amino acid with the help.of enzyme transaminase.
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(c) Formation ofAmides :- The hydoxyl part of the acid is replaced by another amino radicle to form amides. e.g., asparagine and glutamine are formed from aspartic acid and glutamic acid.
