MINERAL NUTRITION
Living organisms bear a number
of macromolecules, similar as carbohydrates, proteins, fats, water and minerals
in order to grow and develop.
Therefore, the inorganic substances or
minerals that give aliment to the living organisms or wftrk as a raw material
for body structure and maintaining its normal functions are nominated as
mineral nutrients and the mode of taking all needed nutrients is called mineral
nutrition. Nutrients are principally divided into two main types
(i) Organic nutrients
(ii) Inorganic nutrients The product of
photosynthesis ( colorful sugars) are considered as organic nutrients, while,
those absorbed by the roots via colorful styles are known as inorganic
nutrients.
In this chapter we will concentrate substantially
on inorganic nutrients.
Styles to Study the Mineral Conditions of Plants
Mineral conditions of Plants was determined by
the culture trial, developed by a prominent German botanist Julius Von Sachs
(1860) for the first time.
Hydroponics or Soilless Culture
This fashion was demonstrated from Julius Von
Sach’s trials that Plants could be grown to their maturity in a well defined
nutrient result indeed in the absence of soil. This fashion of growing plant in
a nutrient result without soil is well known and is also known as water
culture.
The styles involved in hydroponics bear a
veritably careful sanctification of water and nutrient salts. This is essential
in order to assess the part of a particular mineral.
Hydroponic Setup
(a) In hydroponic plant product, Plants are
grown in a tube or trough that are placed in slightly inclined position.
(b) A pump is used to circulate the nutrient
result from the force to the elevated (upper) end of the tube.
(c) Tube is used for adding result (water and
nutrients).
(d) Bent tube is used for aeration.
The nutrient result flows down due to
graveness and returns to the force of the hydroponic setup. In this way, roots
are bathed in aerated nutrient result continuously.
On conducting a series of trials, in which
roots of the Plants were immersed in nutrient result by barring or adding an
element in varied attention. From this, mineral nutrition suitable for the
growth of the plant was attained.
Result Hydroponic revealed the identification
of essential elements for plant growth and also helps in discovering their
insufficiency symptoms.
Conditions Necessary in Hydroponics to Achieve
Optimum Growth
(a) The attention of mineral nutrients must be
constantly maintained.
(b) The result must be aerated adequately for
proper growth and conditioning of roots.
(c) pH of the result is checked from time to
time and corrections are made if necessary.
Uses of Hydroponics
(a) This technique has been successfully
employed for marketable product of vegetables (like tomato, seedless cucumber,
lettice, etc) and also in knowing the toxin of plant (if element is present in
high quantum).
(b) Useful in determining the essential part
of nutrients or mineral elements for the metabolism of plant.
Essential Mineral Nutrients ( Elements)
Essential elements are those which have
structural or physiological part and without which Plants are unfit to complete
their life cycle.
Plants can absorb utmost of the minerals
present in the soil. Further than sixty minerals present in soil have been
recorded essential in Plants out of 105 discovered so far.
Piecemeal from all these elements some Plants
accumulate other elements also, that are heavy and poisonous in nature similar
as silicon, cobalt, selenium and gold. Some other Plants growing near nuclear
test spots also accumulate radioactive elements like strontium.
Still, ways had developed in order to descry
the mineral indeed at veritably low attention,
.i.e., 10 g/ mL. Therefore,
all the elements plant in Plants aren't essential for plant growth and
development.
Criteria
for Quiddity
In order.to determine whether the particular
element is essential or unnecessary, the element must follow the criteria for
quiddity given below
. (i) The element must be
suitable to support normal growth and reduplication, i.e., in the absence of a
particular element, the plant becomes unfit to complete its normal life cycle.
(ii) Demand of the particular element in
applicable quantum must be specific and it shouldn't be replaced by any other
element, i.e., if the insufficiency of one element occurs, it shouldn't be
fulfilled by the addition of some other element.
(iii) The element must be involved directly in
the functioning and metabolism of the plant.
Classification of Essential Mineral Elements
Essential elements do in different proportions
in Plants. On the base of the below mentioned criteria of quiddity some elements
have been plant to be absolutely essential for the normal and better growth,
metabolism and development of Plants.
These elements have been grouped into
following two orders grounded on quantitative conditions.
i.
Macronutrients
These are the elements generally plant in plant
tissues in large quantities (in excess of around 10 m operative kg-1 or 10 mg
per gram of dry matter) and also called major elements. These elements are
generally involved in the conflation of organic motes and development of
osmotic eventuality.
These are carbon, hydrogen, oxygen, nitrogen,
phosphorus, sulphur, potassium, calcium and magnesium. Out of all these elements,
carbon, hydrogen and oxygen are attained from CO2 and H2O while, the others are
attained from the soil.
ii. Micronutrients
These are the elements generally plant in
traces ( veritably small quantum only, i.e., lower than 10 m spook kg-1 or
lower than0.1 mg per gram of dry matter). Micronutrients are generally eight in
number and include iron, manganese, Copper, molybdenum, zinc, boron, chlorine
and nickel. These are substantially involved in the functioning of enzymes as co-factors
or activators of essence.
Differences between Macronutrients and
Micronutrients
Grounded on the different functions of
essential elements, these are also categorised into four other orders given
below
. (i) As the ingredients of
biomolecules These are the essential factors of biomolecules. Hence, known as
the structural elements of cells,e.g., carbon, hydrogen, oxygen and nitrogen.
(ii) As the energy affiliated chemical
composites Some elements also serve in furnishing energy to the cell,e.g.,
Phosphorus is a element of ATP which functions as an energy currency of all the
living systems, while magnesium is a element of chlorophyll, which is involved
in the conversion of light energy into chemical energy.
(iii) As the part of enzymes showing catalytic
goods Numerous of the essential elements are needed in the form of cofactors by
enzymes. They serve as the activator or asset of enzymes,e.g., Mg2 acts as an
activator of several enzymes in both photosynthesis (e.g., Ribulose biphosphate
(RuBP) carboxylase, phosphoenol pyruvate ( Vim) carboxylase) and respiration
(e.g., hexokinase and phosphoffuctokinase).
While Zn2 acts as an activator of alcohol
dehydrogenase and Mo of nitrogenase during the course of fixation of nitrogen.
(iv) As the elements altering osmotic
implicit. Some of the essential elements also alter the Osmotic eventuality.
Utmost of the Osmotic eventuality of cell is due to the inorganic salts. Osmotic
eventuality is necessary for immersion of water and maintaining turgidity of
cell.
Part
of Macro and Micronutrients
The essential elements perform several
important spoilage, most important of them are given below
.1. Regulation of permeability
of cell membrane.
2. Conservation of Osmotic eventuality of cell
tire.
3. Some of them takes part in an electron
transport system.
4. Others serve in softening action, enzymatic
exertion and also serve as a major element of macromolecules andco-enzymes.
Macronutrients
Colorful macronutrients with their sources,
regions and multitudinous junctions are given below
.i. Nitrogen (N)
It's a major element of amino acids, proteins,
nucleic acids, hormones, vitamins, etc. It was the first macronutrient to be
discovered and is needed in veritably large quantum by Plants.
Nitrogen isn't utilised by Plants
directly as similar. It's substantially absorbed in the form of nitrates (NO3),
while others absorb, it in the form of nitrites (NO2) or as ammonium ion (NH4
–)
Region It's generally needed by all corridor
of Plants, substantially the meristematic tissues, and by all the cells, which
are metabolically active in nature Functions Its main function is in growth,
metabolic conditioning and also serves as enzymes in photosynthesis,etc.
Carbon, Hydrogen and Oxygen
. These are although not
considered as mineral elements still, they've an essential part in growth of Plants.
Together they constitute about 94 of the total dry weight of the plant. All of
these are also important part of carbohydrates, fats and proteins.
C, H, O and N are each together called
structural elements because they're the factors of biomolecules of the cell.
ii. Phosphorus (P)
Utmost soils are phosphorus deficient. It's
present in Plants as both organic and inorganic forms. Organic form of phosphorus
isn't absorbed by plant as similar, rather, it's either taken from the solid or
the result phase of soil. It's a element of certain proteins, all nucleic acid
and cell membranes.
The corruption organic form results into an
inorganic form of phosphorus, which is also utilised by the Plants.
It's generally absorbed by roots from soil in
the form of phosphate ions (either as H2PO4 – or HPO42-).
Region: It's needed in all meristems
or youthful tissues and in the regions of developing fruits and seeds.
It generally gets withdrawn from the aged tissues
which becomes metabolically less active. Functions It's substantially involved
in phosphorylation responses and also has its significance in energy transfer
responses. Phosphorus is also present in high energy biomolecules similar as
adenosine triphosphate (ATP) and guanosine triphosphate (GTP). It also has its
major part in growing of grains and fruits.
iii. Potassium (K)
It doesn't acts as a element of any organic
substance, so potassium (K) is available to Plants in its inorganic form
similar as potassium sulphate, potassium nitrate, etc. It's one of the major
ingredients of protoplasm.
Region It's plant in all tissues of Plants
that has the property of differentiating
themselves like meristematic tissues, cub, leaves and root tips.
Its amount is equal in whole plant except in
seeds where it's plant in lower quantity.
Functions It helps in maintaining anion-cation
balance in cells and is also involved in the conflation of proteins. It has its
major part in opening and ending of stomata, in activation of enzymes and also
helps in maintaining the turgidity of cells.
iv. Calcium (Ca)
It's an element which is always plant in green
Plants and is absorbed by them in the form of calcium ions (Ca2) from the soil.
Region It's demanded much in secerning and
meristematic tissues. It gets accumulated mosdy in the aged leaves.
Functions It functions in the conflation of
pectin (calcium pectate) plant in middle lamina of the cell wall during cell
division. It's also involved in the organisation of mitotic spindle. It
activates certain enzymes and plays an important part in the regulation of
cellular conditioning.
v. Magnesium (Mg)
It's the major element of ring structure of
chlorophyll, without which the conformation of chlorophyll doesn't takes place.
It's absorbed by the Plants in the form of a divalent magnesium ion (Mg2) from
the soil.
During stormy season magnesium is percolated
out from the soil due to which its quantum come deficient in Plants.
Region It's needed in growing areas of roots,
stems, seeds.
Functions It helps in the activation of
enzymes of photosynthesis and respiration, in the conformation of chlorophylls,
carotenoids and nucleic acids (DNA and RNA) and to maintain the structure of
ribosome.
vi. Sulphur (S)
It's plant generally in the complex proteins
of Plants.
The most abundant force of sulphur in soil is
in the organic form, similar as lipids, amino acids, proteins,etc.
It's absorbed by the Plants in the form of sulphate
ions (SO42-) from mineral bit of soil.
Region It's needed substantially in youthful
leaves and meristems.
Functions It acts as a major element in amino
acids like cysteine and methionine and. also of several co-enzymes, vitamin
(like thiamin, biotin, coenzyme-A (Co-A) and ferredoxin).
It's due to the presence of
sulphur element in Liliaceae family Plants like onion, garlic,etc., that
they've a characteristic odour.
Micronutrients
Various micronutrients with their sources,
regions and multitudinous functions are given befow
.i. Iron (Fe)
It's needed in huge quantum by Plants in
comparison to other micronutrients. It occurs in the soil substantially in the
form of hydroxides and oxides and is absorbed in the form of ferric ions (Fe3).
Region It's needed by every part of plant but is plant abundantly along modes
of the leaves.
* Excess
amount of
iron is stored as ferritin in Plants.
Functions It's involved in the transfer of
electrons like ferredoxin and cytochromes. Also plays an important part in
responses involving conversion of energy in both photosynthesis and
respiration.
i.e., Fe2 –> Fe3 helps in the development of chloroplasts, chlorophyll and other colors.
ii.Manganese (Mn)
The oxides of manganese are common in soil.
Still, its largely oxidised form isn't available to Plants.
It's absorbed by the Plants in the form of
manganous ions (Mn2).
Region It's needed in leayes and seeds of
plant.
Functions It's helpful is cranking numerous
enzymes that are involved in photosynthesis, respiration and nitrogen
metabolism. It also functions majorly in photolysis of water in order to
liberate oxygen during the process of photosynthesis.
iii. Zinc (Zn)
Zinc is absorbed in the form of Zn2 ions. Zinc
occurs in ferromagnesium minerals. These minerals are survived in order to
liberate bivalent form of Zn2.
It's considered to be more soluble in soil
than other heavy metals.
Region Zinc is needed in every part of the
plant. Functions It helps in activation of colorful enzymes like carboxylases,
oxidases, dehydrogenases, kinases,etc., and also in the conformation of
chlorophyll color. It's also demanded in the conflation of auxin.
iv. Copper (Cu)
It's plant in veritably low quantum in soils.
It's absorbed as cupric ions (Cu2). It acts as a element or activator of
plastocyanin, cytochrome oxidase and numerous other enzymes. Region It's also
needed in every part of Plants like zinc.
Functions Like iron, it's also involved with enzymes that are needed in
redox responses. It can also oxidise in the reversible direction, i.e., from Cu
to Cu2
v. Boron (B)
It's one of the most essential element for the
growth of nearly all Plants, e.g., Tomato, lemon, mustard, cotton,etc.
It's absorbed by the Plants in the form of
BO33-or B4O72-ions from the soil.
Region It's needed substantially by leaves and
seeds.
Functions It's essential in transportation of
carbohydrate through phloem tissues. Boron is demanded for uptake and
utilisation of calcium, in the germination of pollen and root nodulation
extension of cell isolation and carbohydrate translocation.
If pH increases, Still,
vacuity of boron to plant gets diminishments.
vi. Molybdenum (Mo)
The quantum of this element in soil vary
extensively. Plants gain it in the form of molybdate ions (MoO2).
Region It's needed everyplace in Plants but
substantially utilised by roots.
Functions It's an essential element of several
enzymes including two enzymes involved in metabolism of nitrogen, i.e.,
nitrogenase and nitrate reductase. It also has part in reduction of nitrate to
nitrite during the conflation of amino acids.
vii. Chlorine (Cl)
It's abundant in nature. lt is absorbed by the
Plants in the form of chloride ions (Cl). Region It's also needed everyplace
like zinc and Copper. Functions It helps in transfer of electrons from H2O to
photosystem-II in photosynthesis (water splitting response in order to evolve
O2). It's also helpful in determining the attention of solute with Na and K. It
seems to be essential in balancing cationic and anionic rate in cells.
viii. Nickel (A micronutrient)
It's also added as a micronutrient lately.
It's plant to be veritably mobile in Plants and is absorbed by the plant in the
form of Ni2 ions.
Region It's needed in whole plant. Function It acts as an essential part of
enzyme urease which hydrolyse urea —> CO2 NH4. Deficiency symptoms Plant
produces non-viable seeds up to 3rd generation due to its absence and may also
leads to necrotic spots on splint tips.
Deficiency
Symptoms of Essential Elements
The insufficiency symptoms vary from element
to element and they tend to vanish when the particular deficient mineral
nutrient is handed to the plant.
Whenever the force of an essential element
becomes limited, growth of the plant gets retarded. Still, if the privation of
the same nutrient continue for a long period of time, it may ultimately leads
to the death of the plant.
(i) Critical Attention is limited attention of
the essential element below which the growth of plant get reduced, retarded or
stops.
Each essential element plays a vital part in
structural and functional composition of plant. Therefore, in the absence of
any particular element, Plants shows colorful morphologicial changes, which are
reflective of certain element scarcities and are called insufficiency symptoms.
The plant parts show symptoms of insufficiency depending on the mobility of
that element in the plant.
Consequently,
these can also be divided as
. (i) Mobile elements When the
elements are laboriously mobile within the Plants, the symptoms tend to appear
first in aged leaves and tissues. It's because the elements get mobilised from
senescing regions to youthful tissues. For illustration, insufficiency symptoms
of N, K and Mg are visible in the ancient leaves first because these elements
are laboriously mobile. In the aged leaves, biomolecules containing these elements
are broken down, making these elements available for mobilising to youngish
leaves.
(ii) Immobile elements When the elements are
immobile within the Plants, the symptoms appear first in youthful leaves and tissues,
because the elements aren't transported out of the mature organs.
For example, Elements like sulphur and calcium
aren't released out fluently from the plant as they act as an important part of
the structural element of the cell. This aspect (mobility of elements) of
mineral nutrition in Plants play a veritably vital part in husbandry and
horticulture.
Some Major Scarcities in Plants
Colorful kinds of insufficiency symptoms shown
by the Plants are given below
(i) Necrosis It's the miracle, which leads to
the death of tissues, cell or organ substantially leaf tissue, while it's still
a part of the living plant.
It's caused due to the insufficiency of elements
like Ca, Mg, Cu, K,etc.
(ii) Chlorosis It's the loss of chlorophyll
which leads to the yellowing of leaves. This symptom is caused by the
insufficiency of elements like N, K, Mg, S, Fe, Mn, Zn and Mo in Plants.
(iii) Inhibition of cell division It occurs
due to the lack or low situations of elements like N, S, Mo, K,etc.
(iv) Delay unfolding Deficiency of elements,
like N, S, Mo leads to detention in flowering of Plants.
(v) Suppressed plant growth If the low vacuity
of element occurs, it may leads to inhibition of growth in plant and may
ultimately lead to the dwarfing (shortening) of whole plant,e.g.y N, K, Ca, S,
Zn, B, Mo and Cl.
(vi) Unseasonable fall of leaves and kids It's
another type of insufficiency symptom that occurs due to the lack of different
minerals like P, Mg, Cu,etc.
Differences between Necrosis and Chlorosis
Necrosis Chlorosis
Toxin of Micronutrients
A moderate drop of micronutrients beget
insufficiency symptoms, while a moderate increase leads to toxin. Therefore,
whenever the attention of mineral ion in tissues reduces the dry weight by
about 10, it's considered to be poisonous.
The position of toxin varies for different
micronutrients from plant to plant. When the toxin of element increases to
certain position it may also inhibit the uptake of another element.e.g., the
prominent symptom of manganese toxin is the appearance of brown spots girdled
by chlorotic modes.
It's important to know that
manganese competes with iron and magnesium for uptake and with magnesium for
binding with enzymes. Manganese also plays part to inhibit the calcium
translocation in shoot apex.
Thus, presence of manganese in redundant
quantum may, induce scarcities of iron, magnesium and calcium.
Medium
of Immersion and Nitrogen Metabolism
Mineral Immersion
Immersion of mineral salts by Plants from the
soil occurs through the roots substantially from the root hairs and the zones
of immersion. Hence, Plants absorb the minerals from the soil for their
translocation to other corridor of the body through sluice of xylem.
Minerals aren't absorbed as similar by the Plants
rather they're absorbed in their ionic forms.
For example, chlorine isn't absorbed as
similar by the plant insteadly it gets accumulated in the form of chloride
ions.
Mineral
immersion by Plants is done by two different phases:
(i) Original Phase (Passive transport) It's
the pathway by which water or ions present in the free space or external space
of cells are over taken by roots of Plants by taking apoplast pathway ( avoid
entry into cellular membranes and cytoplasm).
In this phase, the plant absorbs mineral
veritably fleetly and doesn't need any metabolic energy in the form of ATP.
Therefore, it's called passive process. The passive movement of ions occur
through ion- channels and the transmembrane proteins that functions as picky
pores into apoplast.
(ii) Metabolic Phase ( Active transport) It's
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 of the
cell. Hence, is called active process.
The movement of ions from cell-to- cell is
called flux. It can be further divided into two main types
(i) Influx (inward movement of ions into the
cells)
(ii) Efflux ( outside movement of ions out of
the cells)
Differences between Active and Passive absorption
Translocation
of Solutes
After absorption the mineral salts passes
readily inward with the transport of water. The translocation of mineral elements
to different parts of the body is done through tracheary elements of the xylem
to reach upward to the leaves and other corridor ( ascent of tire). It's done
through the Plants by the transpirational pull.
Note
• The upward movement of water through stem is
called ascent of sap. It occurs substantially through xylem.
• Minerals pass through xylem (not phloem) is
proved by Stout and Hoaglan in 1939.
Soil as Reservoir of Essential Elements
Soil itself acts as a mineral nutrient force
in natural conditions, but it is not essential for the growth of plant. The
majority of nutrients studied as far are essential for the growth and
development of Plants. These elements become available to the roots of Plants
by the weathering and
breakdown of rocks.
Due to which the soil become enriched with
ions and inorganic salts which are eventually taken up by the Plants itself.
Functions of Soil
Following functions are being performed by the
soil
(i) Soil inventories minerals to plant and
also harbours nitrogen fixing bacteria and other microbes.
(ii) It contains wide variety of substances
essential for plant.
(iii) It holds water and inventories air to
the roots.
(iv) It also acts as a matrix that helps in
stabilisation of plant.
Fertilisers, are the organic or inorganic
accoutrements that are added to soil to supply one or further nutrients which
are essential to the growth of Plants. Since, insufficiency of essential
mineral affects yields of crop therefore, both macro (N, P, K, S, etc) and
micronutrients (Cu, Fe, Zn, Ni, M, B,-etc) acts as element of fertiliser and
applied as per demand.
Metabolism of Nitrogen
Nitrogen exists as two nitrogen atoms joined
by a veritably strong triadic covalent bond ( = ) Nitrogen is Demanded by Plants
for the product of proteins, nucleic acids (DNA and RNA), chlorophyll and
numerous other vitamins. It's also the most prevelant element piecemeal from
carbon, hydrogen and oxygen.
It's absorbed as an inorganic compound which
is changed into its organic form by Plants and certain microbes.
The ultimate source of nitrogen is the
nitrogen gas present in the atmosphere. As nitrogen is limited in nature, Plants
contend with microbes for available nitrogen in the soil. Therefore, nitrogen
acts as a limiting nutrient for both natural and agrarian ecosystems.
Nitrogen
Cycle
It's the process of cycle of events by which
free atmospheric nitrogen is converted into its various chemical forms. The
nitrogen cycle consists of four important processes, i.e., nitrogen- fixation,
ammonification, nitrification and denitrification.
1. Nitrogen- Fixation
In this process, atmospheric nitrogen is fixed
which is to be used by the Plants. In this step, the molecular nitrogen.
converted into inorganic nitrogenous
composites like nitrate, nitrite and ammonia.
Nitrogen fixation is of two types
(i) Physical nitrogen- fixation
(ii) Natural nitrogen- fixation
i.
Physical Nitrogen- Fixation
It's the conversion of N2 to inorganic
nitrogenous composites without the involvement of microorganisms. Fixation
occurs in nature by lightening and ultra violet radiations by which nitrogen
gets converted into its oxides (as NO, NO2, N2O etc) on combining with O2.
These oxides also gets generated by timber fires, artificial combustions and
by. some power generating stations.
ii. Biological Nitrogen- Fixation
The conversion of atmospheric nitrogen into
inorganic nitrogenous composites (nitrate, nitrite and ammonia) through
microorganisms (bacteria, cyanobacteria, etc) are called natural nitrogen- fixation.
As only many organisms use atmospheric nitrogen,
certain prokaryotes are able of fixing nitrogen. The prokaryotic organism that
reduce nitrogen has an enzyme called nitrogenase similar microbes are called 2
fixers.
NEN Nitrogenas
The
organisms that fix nitrogen can be of two types
(a) Asymbiotic or Free living bacteria These
are bacteria that aren't present in close relationship with another bacteria or
other organisms in order to convert nitrogen into ammonia,e.g., number of
cyanobacteria like Anabeana and Nostoc.
The
free living bacteria can also further divided as
• Free living aerobic These include microbes
like Azotobacter and Beijemickia.
• Free living anaerobic These include microbes
like Rhodospirillum and Clostridium.
(b) Symbiotic bacteria These are bacteria the
fixes nitrogen by forming close associations with each other or with another
organism, e.g., relationship between Rhizobium bacteria with legumes and
. mycorrhizae with vascular Plants,etc.
Frankia and Rhizobium, both are unfit to fix
nitrogen when present as free living (aerobes) in soil. But when present as
symbionts they become anaerobes and are suitable to fix atmospheric nitrogen.
Symbiotic Biological Nitrogen- Fixation
The process of symbiosis involves two
organisms living together in different associations. Several types of natural
nitrogen fixing associations are known. The most familiar one is the
relationship of Rhizobium with the roots of several legumes belonging to
class-Leguminosae like sweet pea, lentils, garden pea, alfalfa, sweet clover,
broad bean, clover beans, etc.
They get associated mosdy on the root hair
cells, the root hair coil and the bacteria foray it. An infection thread is
produced carrying the bacteria into the cortex where they initiate root nodule
conformation. Root nodes are small, irregular outgrowth on the roots.
They're internally pinkish in colour due to
the presence of leguminous haemoglobin or leghaemoglobin ( analogous to the
haemoglobin, the red color present in mortal blood).
Symbiotic nitrogen fixing bacteria are also
known to do in the roots of certainnon-leguminous Plants (both angiosperms and
gymnosperms) i.e., Alnus and Cycas independently.
The carnivorous angiosperms (insectivorous Plants)
are autotrophic in nature. But, the strange thing about these Plants is they
behave as heterotrophic organisms for supplementing their nitrogen conditions
by enmeshing insects and other small creatures enzymatically and digesting
them.
They generally grow in water logged soil or wetlands
where the soil is deficient in nitrogen force. Therefore, these Plants fulfil
their need from insects and small creatures by enmeshing them through the
leaves, e.g., Pitcher plant (Nepenthes), Venus fly trap, sundew, water,
flewtrapetc.
Nodule formation
The process of conformation of nodules is a
series of multiple relations that takes place between Rhizobium bacterium and
the root system of legume plant ( host). During the process, bacteria
originally grow in soil near the roots of advanced Plants. They're unfit to fix
nitrogen there, but after coming in contact with the roots of leguminous Plants,
they interact chemically and enter into roots through root hairs.
The process of nodule conformation is as
follows
(i) Rhizobium multiply and colonize itself to
the surrounding of the roots of host plant where it gets physically attached to
the epidermal root hair cells.
(ii) After attachment, the root hair gets
coiled up at the tip due to which bacteria foray the root hair.
(iii) The enzymes from the bacteria degrade
the corridor of root hair cell wall which produces a thread-suchlike structure
called infection thread.
(iv) The bacteria foray the infection thread
and reaches upto the inner cortex of the root.
(v) The bacteria after reaching cortex (mainly
tetraploid cells) stimulate the inauguration of conformation of nodule.
(vi) Bacteria enlarges in size and become
bacteroid ( rod- shaped) therefore, leaving the infection thread and enter the
cells, i.e., inner cortical and pericycle cells to divide.
(vii) This growth and division of pericycle
and cortical cells leads to the conformation of a clump-suchlike structure
called mature root nodule.
(viii) The nodule, therefore formed after
division is eventually responsible for the direct vascular connection with the
host for the exchange of nutrients.
Mature Nodule
The mature Nodule therefore, formed after a
series of events (as bandied over) and chemical changes contains all the
essential biochemical factors i.e., leghaemoglobin and the enzyme nitrogenase.
The enzyme nitrogenase catalyses the conversion of free nitrogen into ammonium,
( first stable product).
The enzyme nitrogenase has two subunits, i.e.,
Fe protein (non-heme iron protein) and Mo-Fe protein (iron molybde-num
protein).
The Fe protein element reacts with ATP and reduces Mo-Fe protein which also reduces 2 to ammonia.
Nitrogenase enzyme, cannot serve in aerobic conditions as it's largely sensitive to molecular oxygen (O2). Therefore, for its exertion it requires anaerobic conditions. Hence, in order to cover this enzyme from oxygen, the nodes produce a substance known as leg-haemoglobin (oxygen scavenger). Nitrogenase isn't active when these microbes lives in aerobic conditions, i.e., free-living but becomes active or functional in anaerobic conditions during events of nitrogen fixation.
Note
• Winograd Sky (I89l) discovered natural
nitrogen fixation.
• The response involving NH3 – conflation by
nitrogenase enzyme requires a veritably high input of energy (8 ATP for each
NH3 produced). The energy needed, therefore, is attained from the respiration
of the host cells.
2. Ammonification
In coming step, organic matter (proteins and
nucleic acids) of the dead remains are perished in order to produce ammonia
(NH3) by microorganisms (like Actinomycetes, Clostridium etc.). Out of the
ammonia product, some of the ammonia gets volatilised and re-enters into the
atmosphere, while utmost of it suffer the process of nitrification by soil
bacteria.
Fate of Ammonia
Nitrogen assimilation results in the
conformation of ammonia which is further used for the conflation of amino acid.
Utmost of the Plants can assimilate both nitrate and ammonium ions (NH4) (the
ammonium ions are formed by the protonation of ammonia at physiological pH).
Ammonium ions are poisonous to Plants and cannot accumulate in them.
Therefore, these 4 are used in
the conflation of amino acids in Plants by following two styles
. (i) Reductive vitality
During this process, the ammonia reacts with a-ketoglutaric acid (organic acid)
and forms an amino acid, i.e., glutamic acid.
(ii) Transamination It's the transfer of amino
group (— NH2) of one amino acid to keto group (C = O) of another keto acid. The
enzyme responsible for this is transaminase or aminotransferase. Glutamic acid
is the main amino acid involved in the conflation of other amino acids through
transamination.
Glutamic acid is substantially responsible for making the transfer of amino group to keto group possible.
Amides
These are generally formed by the combination
of amino acids and ammonia. Their conformation takes place by relief of
hydroxyl ions of amino acid by NH2 ion.
The two most common amides formed in Plants
are aspargine and glutamine formed by the addition of another amino group to
amino acids i.e., aspartic acid and glutamic acid independently,
Uses
of Amides
(i) Both of the amides, i.e., aspargine and
glutamine acts as metabolic budgets. They get accumulated in the towel of
healthy Plants at the time of assimilation of ammonia (if assimilation occurs
in redundant quantum).
(ii) They're translocated to other corridor of
plant through xylem vessels in the form of nitrogen rich composites because
they contain further nitrogen than the amino acids.
In some Plants ureides acts as transporters of
fixed nitrogen along with transpiration stream (e.g., soyabean). These also
have high nitrogen to carbon rate.
3. Nitrification
It's the process in which ammonia produced by the declination of coprolites may not be available to Plants. So, it's first oxidised to nitrite by the soil bacterium Nitrosomonas or Nitrococcus. This nitrite is also farther oxidised to nitrate by another soil bacterium i.e., Nitrobacter. The bacteria which helps in the process of nitrification are inclusively known as chemoautotrophs.
The nitrate therefore, formed are absorbed by Plants and also transported to the leaves where it gets reduced to ammonia that eventually forms amino- group of amino acids.
4. Denitrification
It's the process in which the nitrate present
in the soil is reduced back to free nitrogen (N2). The process of
denitrification is carried out by denitrifying bacteria (like Thiobacillus
denitrificans, Pseudomonas denitrificans etc).
Denitrifying bacteria utilises nitrate and
nitrite ions as electron acceptors in place of oxygen.
