Download Iron (Fe)

Sulfur (S)
Sulfur is an essential element for growth and physiological functioning of plants.
However, its content strongly varies between plant species and it ranges from 0.1 to 6 %
of the plants' dry weight. Sulfates taken up by the roots are the major sulfur source for
growth, though it has to be reduced to sulfide before it is further metabolized. Root
plastids contain all sulfate reduction enzymes, but the reduction of sulfate to sulfide and
its subsequent incorporation into cysteine predominantly takes place in the shoot, in the
chloroplasts. Cysteine is the precursor or reduced sulfur donor of most other organic
sulfur compounds in plants. The predominant proportion of the organic sulfur is present
in the protein fraction (up to 70 % of total sulfur), as cysteine and methionine (two amino
acids) residues. Cysteine and methionine are highly significant in the structure,
conformation and function of proteins. Plants contain a large variety of other organic
sulfur compounds, as thiols (glutathione), sulfolipids and secondary sulfur compounds
(alliins, glucosinolates, phytochelatins), which play an important role in physiology and
protection against environmental stress and pests. Sulfur compounds are also of great
importance for food quality and for the production of phyto-pharmaceutics. Sulfur
deficiency will result in the loss of plant production, fitness and resistance to
environmental stress and pests.
Sulfur is taken up by the roots that have high affinity. The maximal sulfate uptake rate is
generally already reached at sulfate levels of 0.1 mM and lower. The uptake of sulfate by
the roots and its transport to the shoot is strictly controlled and it appears to be one of the
primary regulatory sites of sulfur assimilation. Sulfate is actively taken up across the
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plasma membrane of the root cells, subsequently loaded into the xylem vessels and
transported to the shoot by the transpiration stream. The uptake and transport of sulfate is
energy dependent (driven by a proton gradient generated by ATPases) through a
proton/sulfate co-transport. In the shoot the sulfate is unloaded and transported to the
chloroplasts where it is reduced. The remaining sulfate in plant tissue is predominantly
present in the vacuole, since the concentration of sulfate in the cytoplasm is kept rather
constant.
Metabolic Functions of Sulfur
i)
Sulfur is the constituent of amino acid cystein and methionine and hence
protein and enzymes.
ii)
Both the above amino acids are the precursor of other sulfur containing
enzymes and secondary plant products
iii)
Sulfur is a constituents of several coenzymes and prosthetic groups such as
ferredoxin, biotin (vitamin H) and thaiamin pyrophosphate (vitamin B1).
iv)
Sulpholipid is the structural constituents of biological membrane
v)
Sulpholipids are p[articularly abundant in thylakoid membranes of
chloroplasts
vi)
Sulpholipids are sulfur containing lipids. Sulfoquinovosyl diacylglycerols are
the predominant sulfolipids present in plants. In leaves its content comprises
up to 3 - 6 % of the total sulfur present. This sulfolipid is present in plastid
membranes and likely is involved in chloroplast functioning.
vii)
Volatile compounds such as isothiocyanates and sulfoxides with sulfur as a
structural constituent which are mainly responsible for the characteristics odor
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of seed plant species as onion garlic and mustard.
Isothiocyanate
is the chemical group –N=C=S, formed by substituting sulfur for oxygen in
the isocyanate group. Many natural isothiocyanates from plants are produced
by enzymatic conversion of metabolites called glucosinolates. These natural
isothiocyanates, such as allyl isothiocyanate, are also known as mustard oils.
An artificial isothiocyanate, phenylisothiocyanate, is used for amino acid
sequencing in the Edman degradation.
Sulfur deficiency and plant growth
i)
Sulfur requirement for optimal growth varies between 0.2 and 0.5 % of the
dry weight basis
ii)
Sulfur requirements among the crop families Brassicaceae>Fabaceae>Poacae
iii)
Under condition of sulfur deficiency protein synthesis will impair which leads
to the symptoms of chlorosis.
iv)
Deficiency symptoms show in younger leaves
v)
Thedecrease in the protein content of sulfur-deficient plant is correlated with
the preferential synthesis of protein with lower proportion of methionine and
cystein.
vi) Sulfur deficiency is characterized by stunted growth, and general yellowing of
plants.
vii) In some cases and interveinal pattern appears, the veins remaining green.
viii) Sulfur deficiency may also delay maturity of groundnut crop.
ix) An acute sulfur deficiency causes the entire plant to turn yellow.
Phosphorus Assimilation
i)
Phosphate in the soil solution is readily taken up by plant roots and
incorporate into a variety of organic compounds including sugar phosphates,
phospholipids and nucleotides
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ii)
iii)
iv)
v)
vi)
P is found about 0.2 to 0.8% of the total dry matter
P remains oxidized form in the cell
Remains as esterified through a hydroxyl group to a carbon chain C-O-P
simple phosphate ester (sugar phosphate) or remain as energy phosphate bond
P-P (e.g. ATP)
Another as diester state
Phosphate along with protein/fat are significant constituent of biological
membrane
Biochemical Functions
i)
P as a structural element
a) DNA, RNA
b) Amine choline is often the dominant partner forming phosphotidal choline
(lechithin)
ii)
Role in energy transfer
iii)
ATP and phosphate ester
a) UTP (uridine triphosphate)
b) CTP (cytidine triphosphate)
c) GTP (Guinocine triphosphate)
d) ATP
e) ADP
f) AMP
iv)
NAD and NADP are important in oxidation reduction reaction in which
hydrogen transfer take place.
Regulatory Role of Organic Phosphate
i)
ii)
Pi control some regulatory role of some key enzymes
Can stimulate the phosphofructokinase enzyme which enhances the fruit
ripening of some fruits eg. Tomato
Phosphorus deficiency
All plants may be affected, although this is an uncommon disorder. Undersides of tomato
plant leaves, and the veins and stems, may turn purple. stiff, stunted plants with purlish
tinge.
Phosphorus deficiency is a plant disorder that is most common in areas of high rainfall,
especially on acid, clay or poor chalk soils. Cold weather can cause a temporary
deficiency.
i)
Deficiency is a plant disorder that is most common in areas of high rainfall,
especially on acid, clay or poor chalk soils. Cold weather can cause a
temporary deficiency.
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ii)
iii)
iv)
v)
vi)
vii)
Phosphorus deficiency may be confused with nitrogen deficiency. Some time
similar with N deficiency
Symptoms include poor growth, and leaves that turn blue/green but not
yellow—oldest leaves are affected first. Fruits are small and acid tasting
It is abundantly found in storage and growing organs
Over all stunted plant growth
Dark green or purple color due to anthocyanin pigmentation
Particularly susceptible are carrots, lettuce, spinach, apples, currants and
gooseberries.
Assimilation of Boron (B)
Metabolic Functions of B
i) The primary role of boron is its involvement in the stabilization of the primary cell
walls in plant cells.
ii) Cell elongation, cell division and nucleic acid metabolism
iii) Boron is also involved in the carbohydrate metabolism in plants, protein synthesis,
seed and cell wall formation
iv) Tissue differentiation, auxin and phenol metabolism
v) Membrane permeability
vi) Germination of pollen grains and growth of pollen tubes and sugar translocation.[2]
i) Boron (B) deficiency is an uncommon disorder affecting plants growing in deficient
soils and is often associated with areas of high rainfall and leached soils. Boron may be
present but locked up in soils with a high pH, and the deficiency may be worse in wet
seasons. Most of what is known about boron is from the observations of plants grown in
boron deficient conditions.
ii) Once boron has been absorbed by the plant and incorporated into the various structures
that require boron, it is unable to disassemble these structures and re-transport boron
through the plant resulting in boron being a non-mobile nutrient.[3] This results in the
symptoms of boron deficiency appearing in the young leaves first.
iii) Dicots are much more sensitive to B than monocots
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iv) Terminal leaf become discolor and disorder
v)
Stubby roots formation
Iron (Fe)
Iron is immobile in the plant body
Iron-containing Constituents of Redox System
Two groups of well-defined iron containing proteins:
i) Hemo-protein
Hemoglubin
Peroxidase, catalase
ii) Iron-sulfur proteins- the iron is coordinated to the thiol
group of cystein and/or to inorganic sulphur
Siderophores (Greek: "iron carrier") are small, highaffinity iron chelating compounds secreted by
microorganisms such as bacteria, fungi and grasses.
Siderophores are amongst the strongest soluble Fe3+
binding agents known.
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Metabolic Functions of Fe
i) Protein synthesis where in deficient plants ribosome
content decrease rapidly, increase the number of
aminoacids in chlorotic leaves
ii) Development of chloroplast- synthesis of structural
protein in grana
iii) Formation of chlorophyll is impaired
iv) Carotenoids formation also impared
Deficiency/Toxicity symptoms
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i) Extensive chlorosis in the younger leaf
ii) Inhibition of root elongation
iii) Increase the diameter of apical root zone
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Zinc (Zn)
General
Zinc-containg enzymes
At least four plant enzymes contain bound zinc: alcohol
dehydrogenase, Cu-Zn superoxide dismutase, carbonic
anhydrase,and RNA polymerase
i) Alcohol dehydrogenase
This enzyme catalyzes the reduction of
acetyldehyde to ethanol:
Pyruvate
Acetyldehyde
ethanol
Superoxide dismutase
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In this isoenzyme Zn is associated with copper (CuZn-SOD). The localization and role of SOD have
been discussed.
Carbonic Anhydrase
Carbonic anhydrase (CA) catalyses the hydration of
CO2:
CO2+H2O=HCO3-+H+
Enzyme Activation
Activates various types of enzymes including
dehydrogenase, aldolase, isomerase, transphosphorylase,
RNA and DNA polymerase
Carbohydrate Metabolism
Protein synthesis
Tryptophan and indoleacetic acid synthesis
Phosphorus-Zinc Interactions
Zinc Deficiency and Toxicity
Deficiency
i) Zinc deficiency is widespread among plants grown in
highly weathered acid soils and in calcareous soils.
ii) In calcareousl soils Zn deficiency is often associated
with iron deficiency (lime chlorosis)
iii) The most characteristics visible symptoms of Zinc
deficiency in dicotyledons are stunted growth due to
shortening of internodes (resetting) and a drastic
decrease in leaf size
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iv) Often accompanied with chlorosis
v) Symptoms of chlorosis and necrosis of older leaves of
Zn deficient leaves are the characteristics of P
deficiency.
Zn Toxicity
In crop plants Zn toxicity occurs mainly when sewage
sludge with a high Zn content has been applied.
Copper (Cu)
A)
Copper protein
Copper is present in three different forms in protein:
a) Blue protein- without oxidase activity e.g. plastocyanin
which functions in one-electron transfer
b) Non blue proteins which produce peroxidase and oxidize
mpnophenol to diphenols
c) Multicopper proteins at least four copper atoms per
molecule which act as oxidase (e.g. ascorbate oxidase
and laccase) and catalase the reaction
Superoxide Dismutase (SOD)
Cytochrome oxidase
Ascorbate Oxidase
Phenolase and Laccase
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Amine Oxidase
B)
Carbohydrate and Nitrogen Metabolism
C)
Lignification
Copper Deficiency and Toxicity
i) Stunted growth, distortion of young leaves, necrosis of
the apical meristem
ii) Bleaching of young leaves summer die back in trees
iii) Enhanced formation of tillers in cereals and of
auxillary shoots in dicotyledons are secondary
symptoms caused by necrosis of the apical
meristem.
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Potassium (K)
General Characteristics
i) It is a univalent cation
ii) Characterized by high mobility in plants at all
levels within individual cells, within tissue, as
well as long distance transport via xylem and
phloem
iii) Most abundant cation present in cytoplasm
iv) Luxary uptake is seen when the supply is
adequate
Metabolic and other functions
i)
Enzyme activation- there are more than 50
enzymes which either completely depend on or
are stimulated by K. It an other univalent
cations activate enzymes by conformational
changes of enzymes.
ii) Protein synthesis- it is probable that K is
involved in several steps of translocation
process, including the binding of t RNA to
ribosomes. The role of K in protein synthesis
not only is reflected in the accumulation of
soluble nitrogen compounds.
iii) Photosynthesis- the role of K as the dominant
counter ion to light-induced H+ flux across the
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thlakoid membrane and the establishment of
transmembrane pH gradient necessary for
synthesis of ATP.
iv) Osmoregulation- K+ plays a role in the
process of osmoregulationa) Cell extension
b) Stomatal movement
c) Nyctinastic and seismonastic movement
v) Phloem transport- the high K+ concentration
in the seive tubes are probablely related to the
mechanism of phloem loading of sucrose.
vi) Cation-anion balance- from the viewpoint of
change compensation, K+ is the predominant
cation for counterbalancing immobile anions
in the cytoplasm, and quite often mobile
anions in vacules as well as in the xylem and
phloem.
Deficiency of K
K deficiency, also known as potash deficiency, is a
plant disorder that is most common on light, sandy
soils, because potassium ions (K+) are highly soluble
and will easily leach from soils without colloids.[1]
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Potassium deficiency is also common in chalky or
peaty soils with a low clay content. It is also found on
heavy clays with a poor structure.
i)
ii)
iii)
iv)
v)
vi)
Wilting of leaves
Susceptibility to frost damage
Higher susceptibility to pathogens
Susceptibility to lodging
Ripenning disorder of some fruits
Reduce the yield of tubers
Chlorine (Cl)
i) It is a strange mineral nutrient
ii) It is readily taken up by the plant
iii) The mobility of chlorine is very high both short
distance and long distance transport
iv) Presence in the plant tissue as much as higher than
macro nutrient
Metabolic Functions
i) Photosynthesis and stomatal movement
a) Cl is required in Hill reaction
b) Chloride act as cofactor of the Mn-containing O2evolving system
c) Chloride can affect photosynthesis and plant growth
indirectly via stomatal regulation
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d) Stomatal closer is correlated with corresponding efflux
of accompanying anion (Cl-) in the guard cell
ii) Membrane bound proton pumping ATP-ase
a) Chloride –stimulated H+-ATP-ase is probably of
particular importance
iii) Other effects
a) A specific role of chloride in N metabolism is
indicated by its stimulating effect on asparagines
synthetase. In plant species in which asparagines is the
major compound in the long-distance transport of
soluble N
b) Chloride is one of the major osmotically active solutes
in the vacules and thus affects the turgor potentiality
Deficiency of Chlorine
i)
Cl deficiency seldom occur in plant under field
condition
ii) Severe inhibition of root growth
iii) Decrease the leaf area and plant growth
iv) Wilting of leaf margin is a typical feature and
transpiration
Manganese (Mn2+)
i)
Absorbed as Mn2+ and is translocated
predominantly as free divalent cation in the xylem
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ii)
Can replace the functions of Mg2+
Metabolic Functions
A) Involve the in photosynthetic O2 evolving system
iii) Is required for Hill reaction
iv) Electron transport chain
B) Mn- containing Enzyme
i)
Superoxide dismutase (SOD) (around 90% is
present in chloroplast)
C) Modulation of enzyme activity
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D) Synthesis of protein, carbohydrate and lipids
E) Cell division and extension
Manganese Deficiency and Toxicity
Manganese (Mn) deficiency is a plant disorder that is often
confused with, and occurs with, iron deficiency. Most
common in poorly drained soils, also where organic matter
levels are high. Manganese may be unavailable to plants
where pH is high.
Affected plants include onion, apple, peas, French beans,
cherry and raspberry, and symptoms include yellowing of
leaves with smallest leaf veins remaining green to produce
a ‘chequered’ effect. The plant may seem to grow away
from the problem so that younger leaves may appear to be
unaffected. Brown spots may appear on leaf surfaces, and
severely affected leaves turn brown and wither.
i)
ii)
iii)
iv)
v)
Decrease net Pn and Chl. Content
More susceptible to freezing tempt
Intercostals chlorosis
Manganese induce deficiency of Mg
Ca deficiency also induced by Mn toxicity
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