Microbial Role In Regulatory Mechanisms Of Plants discusses how microbes can help regulate plant growth through direct and indirect mechanisms. Direct mechanisms include nitrogen fixation, phosphate and iron solubilization by microbes like cyanobacteria and rhizobia. Indirect mechanisms involve microbes modulating phytohormone levels, producing antibiotics to inhibit pathogens, and competing with pathogens for resources. Using plant growth promoting bacteria and fungi is a more sustainable alternative to chemicals to increase crop yields and feed a growing population while avoiding environmental harm.
2. Contents
• Introduction
• Why we use microbes
• Plant growth-promoting bacteria(PGPB)
• Mechanism of action of PGPB
• Direct method
• Modulating phytohormone level
• Indirect mechanism
• Conclusion
3. Introduction
Regulatory mechanism
• Regulatory mechanism is necessary for the normal
functioning of living body
• To control and maintaining reactions taking place in the
body
• Maintain within narrow limit
• Any reaction that regulates normal functioning of the
body
• Not only increase size but also numbers
5. Why we use microbes
• There are currently around 7 billion people in the
world and expected to increase approximately 8
billion around the year 2020.
• To feed this growing population, the world needs
to begin to greatly increase agricultural
productivity.
• And to do so in a sustainable and
environmentally friendly manner.
6. • To feed the growing world, it is
necessary to re-examine many of
existing approaches to agriculture.
• Such as the use of:
1. Chemical fertilizers
2. Herbicides
3. Fungicides
4. Insecticides
7. Drawbacks of chemicals
• They are disturbing the symbiotic
association of plants, killing the normal
flora
• Ecological problems.
• Residues have been seen in vegetables
and fruits
• Increase the toxicity of soil profile.
8. Advantages of microbes
• Microbes play important role in
maintaining life on earth.
• Easily available.
• No bad impact on plants and animals.
• Environmental friendly.
9. Plant Growth-Promoting
Bacteria(PGPB)
• Microbes
o Bactria are around 108 to 109 cells per gram of soil
o Other fungi, actinomycites, protozoa, algae also present in soil
• Interaction of microbes with plants are in
3 ways
o Beneficial (bacterium that fixed nitrogen or phosphorus)
o Harmful (IAA overproducing mutant of the bacterium
Pseudomonas fuorescens )
o Neutral (PGPB)
11. Issues in commercialization
of PGPB
• Determination of most important traits that are
effective in working of PGPB strains
• Consistency among regulatory agencies in
different countries regarding to what strains can
be released and in what conditions
• Selection of PGPB strain that function optimally
under specific environmental condition
• Development of more effective mean of applying
PGPB to plant in various settings
13. Nitrogen fixation
• Nitrogen is the most vital nutrient for plant
growth and productivity
• Atmospheric nitrogen can not be utilized
by plants directly
• Conversion of atmospheric nitrogen into
organic nitrogenous compounds is called
nitrogen fixation
15. • Asymbiotic nitrogen fixation:
o Free living nitrogen fixing microorganism.
o E.g. Aerobic and Anaerobic cyanobacteria
• Symbiotic nitrogen fixation:
o Nitrogen fixing microorganism forming mutualistic
association with plant
o E.g. Nodule forming rhizobium
species
16. Steps of nitrogen fixation
• Involves three main
processes:
oAmmonification
oNitrification
oAssimilation
20. Iron solubilization
• Iron is the fourth most abundant element o
earth
• Sparingly soluble, so assimilation by
microorganism is very low
• Rhizoshpores produce compound,
siderophores, which have high affinity for
iron
21. Siderophores
• Low molecular weight ferric iron chelating
compound
• Act as solubilizing agent
• Iron-siderophore complex
• Increase in siderophore producing PGPR,
increase the rate of iron supply to plants
22. Phosphate
Solubilization
• Its amount in soil is between 400 and
1,200mg/kg of soil
• Insoluble phosphorus is present as
• inorganic mineral
o (apatite)
• organic forms
o inositol phosphate (soil phytate), phosphomonesters, and
phosphotriesters
23. Solubilization
• the solubilization of inorganic phosphorus occurs as a
consequence of the action of low molecular weight
organic acids such as gluconic and citric acid, both of
which are synthesized by various soil bacteria.
• mineralization
• The mineralization of organic phosphorus occurs through
the synthesis of a variety of different phosphatases,
catalyzing the hydrolysis of phosphoric esters.
24.
25. Sulphur solublization
• Sulfur is part of some amino acids (cysteine and
methionine) and of proteins.
• The presence of cysteine in proteins allows the
formation of disulfide bonds
• Sulfur is also contained glutathione
• Soil microorganisms can affect sulfur forms and
availability in four ways:
•
26. • Through oxidation
• Through reduction
• Through immobilization
• Through mineralization
• Many soil bacteria are able to use
sulfur as a source of energy i.e.
Thiobacillus sp.
27.
28. Modulating
phytoharmone level
• Cytokinins
• They are synthesized in roots and then
transported into other parts of plants
• Its functions are
o Stimulation of cell division
o Shoot initiation
o Leaf cell enlargement
• Cytokinins have been detected in the cell-free
medium of some strains of Azotobacter spp.
29. Auxin
• The naturally producing auxin is , indole-
3aceticacid(indoleaceticacid,IAA)
• function
o affects plant cell division
o stimulates seed and tuber germination
o increases the rate of xylem and root development
• IAA synthesized by bacteria may be
involved at different levels i.e. , plant
growth promotion and root nodulation
30. Ethylene
• The plant hormone ethylene has a wide
range of biological activities and is
activated at concentration of 0.05 µl/L and
in fruit ripening its level is 200 µl/L.
• Functions
o promoting root initiation
o inhibiting root elongation
o Promoting fruit ripening
31. • The ethylene that is synthesized as a
response to various stresses is called
“stress ethylene”
• plants that are exposed to stress
quickly respond by producing a small
peak of ethylene that initiates a
protective response by the plant
32. INDIRECT
MECHANISM
• A phenomena in which microbes produced
toxins which are antioxidants to others.
METHODS OF INDIRECT MECHANISM
(1) Antibiotics and lytic enzymes
(2) Induced systematic resistance
(3) Ethylene
(4) Siderophores
(5) Competition
33. Antibiotics and lytic
enzymes
• The synthesis of a range of different
antibiotics is the PGPB trait that is most
often associated with the ability of the
bacterium to prevent the proliferation of
the plant pathogens.
• One problem with depending too much on
antibiotic producing bacteria as biocontrol
agent is that some phytopathogens may
develop resistance to specific antibiotics.
34. • To prevent this ,researchers have
utilized biocontrol strains that
synthesize HCN as well as one or
more antibiotics.
• Some biocontrol bacteria produce
enzymes including
o chitinases
o cellulases
o proteases
o lipases
35. Induced systematic
resistance
• PGPB can trigger a phenomena in plants
known as ISR.
• It is similar to SAR that occurs when plants
activate their defense mechanism in
response to infection by a pathogenic
agent.
36. • ISR said to be “primed” so that they react
faster and most strongly to pathogen
attack by inducing defense mechanisms.
• ISR involves JASMONATE and
ETHYLENE signaling with plants defense
responses to a range of pathogens
37. Siderophores
● Some bacterial strains, that do not employ any other
mean of biocontrol can act as biocontrol agent.
● Prevent plants from pathogens by limiting iron
proliferation.
● Effective for fungal pathogens.
● Effective because siderophores have much capability of
binding Iron than do fungal pathogens.
38. Compitition
● Some indirect evidence indicates that
Compitition between pathogens can limit
disease severity.
● Non pathogenic soil microbes rapidly
colonize on plant surface & use most of
available nutrients.
e.g
Treatment of plants with leaf bacterium
"sphinogomones sp. "
39. Conclusion
• Regulatory mechanism plays an important
role in growth of plants
• They are enhanced by using either
chemical fertilizer or PGPB
• Synthetic compounds are harmful for
plants, so we are adopting microbe
mediated regulatory mechanisms.
