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 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 plastidmembranes 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 of seed plant species as onion garlic and mustard. Isothiocyanateis 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
ii)P is found about 0.2 to 0.8% of the total dry matter
iii)P remains oxidized form in the cell
iv)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)
v)Another as diester state
vi)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)Pi control some regulatory role of some key enzymes
ii)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 chalksoils. 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 chalksoils. Cold weather can cause a temporary deficiency.
ii)Phosphorus deficiency may be confused with nitrogen deficiency. Some time similar with N deficiency
iii)Symptoms include poor growth, and leaves that turn blue/green but not yellow—oldest leaves are affected first. Fruits are small and acid tasting
iv)It is abundantly found in storage and growing organs
v)Over all stunted plant growth
vi)Dark green or purple color due to anthocyanin pigmentation
vii) 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
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, high-affinity ironchelating compounds secreted by microorganisms such as bacteria, fungi and grasses.Siderophores are amongst the strongest soluble Fe3+ binding agents known.
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
i)Extensive chlorosis in the younger leaf
ii) Inhibition of root elongation
iii)Increase the diameter of apical root zone
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
In this isoenzyme Zn is associated with copper (Cu-Zn-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
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
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.
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 thlakoid membrane and the establishment of transmembrane pH gradient necessary for synthesis of ATP.
iv)Osmoregulation- K+ plays a role in the process of osmoregulation-
a)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] 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)Wilting of leaves
ii)Susceptibility to frost damage
iii)Higher susceptibility to pathogens
iv)Susceptibility to lodging
v)Ripenning disorder of some fruits
vi)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 O2-evolving system
c)Chloride can affect photosynthesis and plant growth indirectly via stomatal regulation
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
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
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)Decrease net Pn and Chl. Content
ii)More susceptible to freezing tempt
iii)Intercostals chlorosis
iv)Manganese induce deficiency of Mg
v)Ca deficiency also induced by Mn toxicity
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