Biological Nitrogen Fixation
Contents:
Introduction
Methods for measuring N2 fixation
1. Ntrogen balance method
2. Nitrogen difference method
3. Ureides method
4.〖𝟏𝟓〗_𝑵 isotope techniques
5. Acetylene reduction assay
6. Hydrogen evolution method
Introduction
N2 gas are found 78.084%on atmosphere of earth.
Nitrogen is an essential element for plant growth and development and a key issue of agriculture.
N2 are found in molecular N2 (𝑵 ≡ 𝑵) form in soil.
Dinitrogen is more stable, so we need of nitrogen fixation.
Most studies indicate that nitrogen fertilizers contribute to resolving the challenge the world is facing, feeding the human population.
The Green revolution was accompanied by an enormous increase in the application of nitrogen fertilizer.
Nitrogen fixation is a process by which nitrogen of the Earth's atmosphere is converted into ammonia (NH3), nitrogen salts or other molecules available to living organisms.
Biological Nitrogen Fixation(BNF) is known to be a sustain agriculture and increase soil fertility.
Research on microorganisms and plants able to fix nitrogen contributes largely to the production of bio fertilizers.
Thus it is important to ensure that BNF research and development will take into account the needs of farmers in the developing countries mainly.
Role of nitrogen in Plant
Sources of Nitrogen
Why measure 𝑵_𝟐 fixation?
Ecological consideration require an understanding of the relative contribution of 𝑵_𝟐 fixing components to the N-cycle.
Measurement of 𝑁_2 fixation enable an investigator to evaluate the ability of indigenous Rhizobium spp. to effectively nodulate newly introduced legumes.
Development of sustainable farming systems.
Understanding of the amount of 𝑵_𝟐fixed by legumes as influenced by soil management or cultural practices allows development of efficient agricultural and agroforesty production systems.
Biological Nitrogen Fixation
Contents:
Introduction
Methods for measuring N2 fixation
1. Ntrogen balance method
2. Nitrogen difference method
3. Ureides method
4.〖𝟏𝟓〗_𝑵 isotope techniques
5. Acetylene reduction assay
6. Hydrogen evolution method
Introduction
N2 gas are found 78.084%on atmosphere of earth.
Nitrogen is an essential element for plant growth and development and a key issue of agriculture.
N2 are found in molecular N2 (𝑵 ≡ 𝑵) form in soil.
Dinitrogen is more stable, so we need of nitrogen fixation.
Most studies indicate that nitrogen fertilizers contribute to resolving the challenge the world is facing, feeding the human population.
The Green revolution was accompanied by an enormous increase in the application of nitrogen fertilizer.
Nitrogen fixation is a process by which nitrogen of the Earth's atmosphere is converted into ammonia (NH3), nitrogen salts or other molecules available to living organisms.
Biological Nitrogen Fixation(BNF) is known to be a sustain agriculture and increase soil fertility.
Research on microorganisms and plants able to fix nitrogen contributes largely to the production of bio fertilizers.
Thus it is important to ensure that BNF research and development will take into account the needs of farmers in the developing countries mainly.
Role of nitrogen in Plant
Sources of Nitrogen
Why measure 𝑵_𝟐 fixation?
Ecological consideration require an understanding of the relative contribution of 𝑵_𝟐 fixing components to the N-cycle.
Measurement of 𝑁_2 fixation enable an investigator to evaluate the ability of indigenous Rhizobium spp. to effectively nodulate newly introduced legumes.
Development of sustainable farming systems.
Understanding of the amount of 𝑵_𝟐fixed by legumes as influenced by soil management or cultural practices allows development of efficient agricultural and agroforesty production systems.
Biological nitrogen fixation (BNF) can be defined as the conversion of atmospheric dinitrogen (N2) to ammonia (NH3) under the combined action of biological and chemical activities
A biotechnology dream nitrogen fixing cereal crops by Deepak Sharma Deepak Sharma
The presentation discuss about the present studies going on regarding biological nitrogen fixation in cereals. The material collected is recent one and includes all the potential studies and researches going around the world. the information given includes the pathways, the genetics, molecular mechanism, and results of various experiments and potential solutions. It describe all the possible ways and shows the future possibilities to achieve this dream.
It is a biofertilizer that contains symbiotic Rhizobium bacteria which is the most important nitrogen-fixing organism. These organisms have the ability to drive atmospheric Nitrogen and provide it to plants. It is recommended for crops such as Groundnut, Soybean, Red-gram, Green-gram, Black-gram, Lentil, Cowpea, Bengal-gram and Fodder legumes, etc.
Quality control and constraints in biofertilizer production technologyVENKATESH AGRI
Biofertilizers or microbial inoculants are the carrier-based preparations containing sufficient number of microorganisms in a viable state inoculated to soil or seed to augment the nutrient availability to plant by enhancing the growth and proliferation of microorganisms.
CS_701_Nitrate Assimilation by arnold_damasoAr R Ventura
Nitrate assimilation is the formation of organic nitrogen compounds like amino acids from inorganic nitrogen compounds present in the environment. Organisms like plants, fungi and certain bacteria that cannot fix nitrogen gas (N2) depend on the ability to assimilate nitrate or ammonia for their needs.
Plants like castor reduce a lot of nitrate in the root itself, and excrete the resulting base. Some of the base produced in the shoots is transported to the roots as salts of organic acids while a small amount of the carboxylates are just stored in the shoot itself. However, about 99% of the organic nitrogen in the biosphere is derived from the assimilation of nitrate. NH4+ is formed as an end product of the degradation of organic matter, primarily by the metabolism of animals and bacteria, and is oxidized to nitrate again by nitrifying bacteria in the soil. Thus a continuous cycle exists between the nitrate in the soil and the organic nitrogen in the plants growing on it. While nearly all the ammonia in the root is usually incorporated into amino acids at the root itself, plants may transport significant amounts of ammonium ions in the xylem to be fixed in the shoots. This may help avoid the transport of organic compounds down to the roots just to carry the nitrogen back as amino acids.
Mechanism of Zinc solubilization by Zinc Solubilizing bacteriasJaison M
M.Sc. Credit Seminar
One of the way to manage Zn deficiency is by using Bacteria which have potentiality of solubilization of insoluble forms of Zinc. Some mechanisms have been reported for solubilisation of zinc by bacteria which are acidolysis, extrusion of protons, mineralization of zinc fractions, production of zinc binding proteins and complexation by organic acids.
Biological nitrogen fixation (BNF) can be defined as the conversion of atmospheric dinitrogen (N2) to ammonia (NH3) under the combined action of biological and chemical activities
A biotechnology dream nitrogen fixing cereal crops by Deepak Sharma Deepak Sharma
The presentation discuss about the present studies going on regarding biological nitrogen fixation in cereals. The material collected is recent one and includes all the potential studies and researches going around the world. the information given includes the pathways, the genetics, molecular mechanism, and results of various experiments and potential solutions. It describe all the possible ways and shows the future possibilities to achieve this dream.
It is a biofertilizer that contains symbiotic Rhizobium bacteria which is the most important nitrogen-fixing organism. These organisms have the ability to drive atmospheric Nitrogen and provide it to plants. It is recommended for crops such as Groundnut, Soybean, Red-gram, Green-gram, Black-gram, Lentil, Cowpea, Bengal-gram and Fodder legumes, etc.
Quality control and constraints in biofertilizer production technologyVENKATESH AGRI
Biofertilizers or microbial inoculants are the carrier-based preparations containing sufficient number of microorganisms in a viable state inoculated to soil or seed to augment the nutrient availability to plant by enhancing the growth and proliferation of microorganisms.
CS_701_Nitrate Assimilation by arnold_damasoAr R Ventura
Nitrate assimilation is the formation of organic nitrogen compounds like amino acids from inorganic nitrogen compounds present in the environment. Organisms like plants, fungi and certain bacteria that cannot fix nitrogen gas (N2) depend on the ability to assimilate nitrate or ammonia for their needs.
Plants like castor reduce a lot of nitrate in the root itself, and excrete the resulting base. Some of the base produced in the shoots is transported to the roots as salts of organic acids while a small amount of the carboxylates are just stored in the shoot itself. However, about 99% of the organic nitrogen in the biosphere is derived from the assimilation of nitrate. NH4+ is formed as an end product of the degradation of organic matter, primarily by the metabolism of animals and bacteria, and is oxidized to nitrate again by nitrifying bacteria in the soil. Thus a continuous cycle exists between the nitrate in the soil and the organic nitrogen in the plants growing on it. While nearly all the ammonia in the root is usually incorporated into amino acids at the root itself, plants may transport significant amounts of ammonium ions in the xylem to be fixed in the shoots. This may help avoid the transport of organic compounds down to the roots just to carry the nitrogen back as amino acids.
Mechanism of Zinc solubilization by Zinc Solubilizing bacteriasJaison M
M.Sc. Credit Seminar
One of the way to manage Zn deficiency is by using Bacteria which have potentiality of solubilization of insoluble forms of Zinc. Some mechanisms have been reported for solubilisation of zinc by bacteria which are acidolysis, extrusion of protons, mineralization of zinc fractions, production of zinc binding proteins and complexation by organic acids.
Nitrogen is one of the most important major limiting nutrients for most crops and other plant species. Biological Nitrogen Fixation (BNF) is an ecologically important phenomenon that can support an amount of nitrogen to compensate the difficiencies of this element. In this biologically-mediated process, a specific group of bacteria, collectivelly called rhizobia, fixed atomospheric dinitrogen (N2) via symbioses with legumes.Other free living bacteria fix nitrogen in the soil or in non specific association with plants. This biological process between rhizobium strains and their legume partners can be happened under low level of available nitrogen with help of many different genes such as nod, nif, fix, production of polysaccharides, competition, infection process, host specificity, Type I to Type VI secretion, signals of host and many other different genes that recently have been reported by scientists. The establishment of the symbiosis requires close coordination between the partners and is mediated by the exchange of diffusible signal molecules. Most recently, bacterial and plant genome-sequencing projects have added immensely to the resources available to study the symbiosis. A major event was the adoption of two genetic model legumes, Lotus japonicus and Medicago truncatula, and the genomes of both plants are currently being sequenced.Research with these model plants has now revealed the basic outlines of the plant-signaling pathways that lead to nodule formation.
Nitrogen-fixing bacteria, microorganisms capable of transforming atmospheric nitrogen into fixed nitrogen (inorganic compounds usable by plants). More than 90 percent of all nitrogen fixation is effected by these organisms, which thus play an important role in the nitrogen cycle.
Two kinds of nitrogen-fixing bacteria are recognized. The first kind, the free-living (nonsymbiotic) bacteria, includes the cyanobacteria (or blue-green algae) Anabaena and Nostoc and genera such as Azotobacter, Beijerinckia, and Clostridium. The second kind comprises the mutualistic (symbiotic) bacteria; examples include Rhizobium, associated with leguminous plants (e.g., various members of the pea family); Frankia, associated with certain dicotyledonous species (actinorhizal plants); and certain Azospirillum species, associated with cereal grasses.
The symbiotic nitrogen-fixing bacteria invade the root hairs of host plants, where they multiply and stimulate formation of root nodules, enlargements of plant cells and bacteria in intimate association. Within the nodules the bacteria convert free nitrogen to ammonia, which the host plant utilizes for its development. To ensure sufficient nodule formation and optimum growth of legumes (e.g., alfalfa, beans, clovers, peas, soybeans), seeds are usually inoculated with commercial cultures of appropriate Rhizobium species, especially in soils poor or lacking in the required bacterium.
Slide 1: Title Slide
Extrachromosomal Inheritance
Slide 2: Introduction to Extrachromosomal Inheritance
Definition: Extrachromosomal inheritance refers to the transmission of genetic material that is not found within the nucleus.
Key Components: Involves genes located in mitochondria, chloroplasts, and plasmids.
Slide 3: Mitochondrial Inheritance
Mitochondria: Organelles responsible for energy production.
Mitochondrial DNA (mtDNA): Circular DNA molecule found in mitochondria.
Inheritance Pattern: Maternally inherited, meaning it is passed from mothers to all their offspring.
Diseases: Examples include Leber’s hereditary optic neuropathy (LHON) and mitochondrial myopathy.
Slide 4: Chloroplast Inheritance
Chloroplasts: Organelles responsible for photosynthesis in plants.
Chloroplast DNA (cpDNA): Circular DNA molecule found in chloroplasts.
Inheritance Pattern: Often maternally inherited in most plants, but can vary in some species.
Examples: Variegation in plants, where leaf color patterns are determined by chloroplast DNA.
Slide 5: Plasmid Inheritance
Plasmids: Small, circular DNA molecules found in bacteria and some eukaryotes.
Features: Can carry antibiotic resistance genes and can be transferred between cells through processes like conjugation.
Significance: Important in biotechnology for gene cloning and genetic engineering.
Slide 6: Mechanisms of Extrachromosomal Inheritance
Non-Mendelian Patterns: Do not follow Mendel’s laws of inheritance.
Cytoplasmic Segregation: During cell division, organelles like mitochondria and chloroplasts are randomly distributed to daughter cells.
Heteroplasmy: Presence of more than one type of organellar genome within a cell, leading to variation in expression.
Slide 7: Examples of Extrachromosomal Inheritance
Four O’clock Plant (Mirabilis jalapa): Shows variegated leaves due to different cpDNA in leaf cells.
Petite Mutants in Yeast: Result from mutations in mitochondrial DNA affecting respiration.
Slide 8: Importance of Extrachromosomal Inheritance
Evolution: Provides insight into the evolution of eukaryotic cells.
Medicine: Understanding mitochondrial inheritance helps in diagnosing and treating mitochondrial diseases.
Agriculture: Chloroplast inheritance can be used in plant breeding and genetic modification.
Slide 9: Recent Research and Advances
Gene Editing: Techniques like CRISPR-Cas9 are being used to edit mitochondrial and chloroplast DNA.
Therapies: Development of mitochondrial replacement therapy (MRT) for preventing mitochondrial diseases.
Slide 10: Conclusion
Summary: Extrachromosomal inheritance involves the transmission of genetic material outside the nucleus and plays a crucial role in genetics, medicine, and biotechnology.
Future Directions: Continued research and technological advancements hold promise for new treatments and applications.
Slide 11: Questions and Discussion
Invite Audience: Open the floor for any questions or further discussion on the topic.
Seminar of U.V. Spectroscopy by SAMIR PANDASAMIR PANDA
Spectroscopy is a branch of science dealing the study of interaction of electromagnetic radiation with matter.
Ultraviolet-visible spectroscopy refers to absorption spectroscopy or reflect spectroscopy in the UV-VIS spectral region.
Ultraviolet-visible spectroscopy is an analytical method that can measure the amount of light received by the analyte.
Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
Introduction:
RNA interference (RNAi) or Post-Transcriptional Gene Silencing (PTGS) is an important biological process for modulating eukaryotic gene expression.
It is highly conserved process of posttranscriptional gene silencing by which double stranded RNA (dsRNA) causes sequence-specific degradation of mRNA sequences.
dsRNA-induced gene silencing (RNAi) is reported in a wide range of eukaryotes ranging from worms, insects, mammals and plants.
This process mediates resistance to both endogenous parasitic and exogenous pathogenic nucleic acids, and regulates the expression of protein-coding genes.
What are small ncRNAs?
micro RNA (miRNA)
short interfering RNA (siRNA)
Properties of small non-coding RNA:
Involved in silencing mRNA transcripts.
Called “small” because they are usually only about 21-24 nucleotides long.
Synthesized by first cutting up longer precursor sequences (like the 61nt one that Lee discovered).
Silence an mRNA by base pairing with some sequence on the mRNA.
Discovery of siRNA?
The first small RNA:
In 1993 Rosalind Lee (Victor Ambros lab) was studying a non- coding gene in C. elegans, lin-4, that was involved in silencing of another gene, lin-14, at the appropriate time in the
development of the worm C. elegans.
Two small transcripts of lin-4 (22nt and 61nt) were found to be complementary to a sequence in the 3' UTR of lin-14.
Because lin-4 encoded no protein, she deduced that it must be these transcripts that are causing the silencing by RNA-RNA interactions.
Types of RNAi ( non coding RNA)
MiRNA
Length (23-25 nt)
Trans acting
Binds with target MRNA in mismatch
Translation inhibition
Si RNA
Length 21 nt.
Cis acting
Bind with target Mrna in perfect complementary sequence
Piwi-RNA
Length ; 25 to 36 nt.
Expressed in Germ Cells
Regulates trnasposomes activity
MECHANISM OF RNAI:
First the double-stranded RNA teams up with a protein complex named Dicer, which cuts the long RNA into short pieces.
Then another protein complex called RISC (RNA-induced silencing complex) discards one of the two RNA strands.
The RISC-docked, single-stranded RNA then pairs with the homologous mRNA and destroys it.
THE RISC COMPLEX:
RISC is large(>500kD) RNA multi- protein Binding complex which triggers MRNA degradation in response to MRNA
Unwinding of double stranded Si RNA by ATP independent Helicase
Active component of RISC is Ago proteins( ENDONUCLEASE) which cleave target MRNA.
DICER: endonuclease (RNase Family III)
Argonaute: Central Component of the RNA-Induced Silencing Complex (RISC)
One strand of the dsRNA produced by Dicer is retained in the RISC complex in association with Argonaute
ARGONAUTE PROTEIN :
1.PAZ(PIWI/Argonaute/ Zwille)- Recognition of target MRNA
2.PIWI (p-element induced wimpy Testis)- breaks Phosphodiester bond of mRNA.)RNAse H activity.
MiRNA:
The Double-stranded RNAs are naturally produced in eukaryotic cells during development, and they have a key role in regulating gene expression .
Cancer cell metabolism: special Reference to Lactate PathwayAADYARAJPANDEY1
Normal Cell Metabolism:
Cellular respiration describes the series of steps that cells use to break down sugar and other chemicals to get the energy we need to function.
Energy is stored in the bonds of glucose and when glucose is broken down, much of that energy is released.
Cell utilize energy in the form of ATP.
The first step of respiration is called glycolysis. In a series of steps, glycolysis breaks glucose into two smaller molecules - a chemical called pyruvate. A small amount of ATP is formed during this process.
Most healthy cells continue the breakdown in a second process, called the Kreb's cycle. The Kreb's cycle allows cells to “burn” the pyruvates made in glycolysis to get more ATP.
The last step in the breakdown of glucose is called oxidative phosphorylation (Ox-Phos).
It takes place in specialized cell structures called mitochondria. This process produces a large amount of ATP. Importantly, cells need oxygen to complete oxidative phosphorylation.
If a cell completes only glycolysis, only 2 molecules of ATP are made per glucose. However, if the cell completes the entire respiration process (glycolysis - Kreb's - oxidative phosphorylation), about 36 molecules of ATP are created, giving it much more energy to use.
IN CANCER CELL:
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
introduction to WARBERG PHENOMENA:
WARBURG EFFECT Usually, cancer cells are highly glycolytic (glucose addiction) and take up more glucose than do normal cells from outside.
Otto Heinrich Warburg (; 8 October 1883 – 1 August 1970) In 1931 was awarded the Nobel Prize in Physiology for his "discovery of the nature and mode of action of the respiratory enzyme.
WARNBURG EFFECT : cancer cells under aerobic (well-oxygenated) conditions to metabolize glucose to lactate (aerobic glycolysis) is known as the Warburg effect. Warburg made the observation that tumor slices consume glucose and secrete lactate at a higher rate than normal tissues.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
This presentation explores a brief idea about the structural and functional attributes of nucleotides, the structure and function of genetic materials along with the impact of UV rays and pH upon them.
5. Root nodule symbiosis
Most plants that form
nitrogen-fixing nodules
are legumes. Their
partners are diverse
bacteria collectively
called rhizobia
Unrelated Frankia
bacteria nodulate a
diverse group of
plants called
actinorhizal plants
Casuarina equisetifolia
Root nodules of the legume
Medicago truncatula inoculated
with Sinorhizobium meliloti
6. Root nodule symbiosis is a mutually
beneficial arrangement
N2 N2
NH4
+
Glutamine
NH4
+
CO2
Light
Carbohydrate
Legume with
nitrogen-fixing
nodule
Bartering reduced molecules
The plant provides organic carbon
derived from photosynthesis, and
the bacteria provide fixed nitrogen.
Most rhizobia cannot fix nitrogen
except in nodules
8. Biological nitrogen fixation
2 NH3
N2
Nitrogenase
16 ATP
Many prokaryotes can fix nitrogen
using an enzyme called
nitrogenase. This process uses a
great deal of cellular energy, ATP.
3 H2
9. Symbiotic nitrogen fixation
Actinorhizal plants like
alder with symbiotic
Frankia bacteria
Legumes with
symbiotic
rhizobia
Some nitrogen-
fixing bacteria
form an intimate
partnership with
plants in the
form of nitrogen-
fixing nodules
10. The rhizobia-legume symbiosis
• The most sophisticated N2-
fixing symbiosis
• The nodule is a unique root
organ designed to support
endosymbiotic rhizobia and
N2-fixation
• Upon infection, the rhizobia
differentiate into bacteroids
• Bacteroids are enclosed in
the plant cell by the
symbiosome
• Symbiosomes are
surrounded by a specialized
plant membrane - the
peribacteroid membrane.
Root nodules
Cross-section of the
nodule
Bacteroids inside symbiosomes
Bacteroids inside a
nodule
10 μm
11. Legumes are important ecologically
and as food and fodder crops
Lupines and other legumes are
pioneer plants that can grow in
disturbed or infertile soils
Some legumes are too
successful and become a
pest, such as the
invasive legume kudzu
(Pueraria montana)
Legumes provide protein to
humans and other animals
13. Steps in nodule development
Communication
Root hair
curling
Infection
thread
formation
Cell
division
in root
Nodule
expressing
leghemoglobin
Generalized steps in the formation of a nodule
N2
NH4
+
Bacteroid
Plant root
Rhizobia
14. Communication:
Flavonoids and Nod factors
1. The plant root
produces specific
flavonoids that
attract rhizobia
2. Most rhizobia produce
Nod factors, identifying
them as appropriate
symbionts
3. The plant prepares to
form a symbiotic nodule
structure
Rhizobia
Plant cell
15. Nod factor perception induces root
hair curling
• Nod-factors are
concentrated in the
cell wall and are
almost immobile
• Nod-factors cause
redirection of tip
growth (shown in a)
• Only a few bacteria
actually redirect the
growth of the root hair
successfully and
become enveloped in
an infection thread
time
16. Bacterial entry and nodulation process
1. Root hair curling
2. Infection thread (IT)
formation and cortical cell
division (CCD)
3. Nodule primordium (NP)
formation
4. Nodule development with
formation of nodule
meristem (in some
legumes)
17. Symbiotic nitrogen fixation requires
teamwork
N2 N2
NH4
+
Gln
NH4
+
CO2
Light
Carbohydrate
Plants cannot fix nitrogen on
their own, and most rhizobia
cannot fix nitrogen on their
own.
Symbiotic nitrogen fixation is
a true partnership.
The bacteria provide
nitrogenase.
The host plant provides
leghemoglobin,
homocitrate, carbon
sources, organic
nitrogen…..
18. Bacteroids need a high O2 flux but low O2
environment
C6H12O6
O2
A high affinity cytochrome
oxidase in the bacteroid
functions at low oxygen
concentrations
A low oxygen environment
is maintained by an oxygen
permeability barrier
Oxidative phosphorylation
requires oxygen for ATP
production
Leghemoglobin buffers
oxygen and deliver it to
respiring symbiotic cells
Leghemoglobin gives
nodules their pink
colour
19.
20. WHY TO FOCUS CEREALS?
• Top consumed crops
belong to this
category.
high yielding varities
during green revolution.
• Need large amount of
inorganic fertilizers.
• Comparatively low N
use efficiency.
21. CEREALS….. BUT HOW?
• Engineering cereal crops to fix nitrogen
without compromising their yield potential.
• Possible if the ability to percieve rhizobial
signaling molecules and formation of an
oxygen-limited, nodule-like root organ can be
transferred to cereal plants.
• Potential criticism: cereals is the potential for
a yield penalty associated with the increased
demand on photosynthates required to
support nitrogen fixation.
22. BIOTECHNOLOGICAL APPROACHES TO
TARGET CEREALS
• Transferring the legume-rhizobial interaction to cereals roots.
• Utilizing endophytic diazotrophs that infect cereals to fix nitrogen
for their host plants.
• Introduction of nitrogenase enzyme into organelles of plant cells to
create a new nitrogen-fixing capability.
Highly complex enzyme
High energetic emands
Irreversibly denatured by oxygen
23. TRANSFERRING THE LEGUME-RHIZOBIAL
INTERACTION TO CEREALS ROOTS
• Nod Factor: the signaling molecule
• Four genetic processes to be introduced
–Recognition of Nod factors
–Organogenesis of the root nodule
–Bacterial infection
–Establishment of a suitable environment for
nitrogenase activity inside the nodule
24. The connecting link: SYM Pathway
• Nod factors and Myc factors perception leads to the
activation.
• Well conserved between legumes and monocotyledons
• The SYM pathway present in cereals and essential for
supporting the mycorrhizal symbiosis.
• A number of OoSYM signalling components (CASTOR,
CCaMK, and CYCLOPS): complement legume mutants,
not only for mycorrhization, but also for nodulation.
– Longer domain length versions: able to support nodulation
signalling.
25. Conti…
• Nitrogen fixation: transferred from Klebsiella to E.
coli in 1972
• But transfer to a eukaryote (including a plant) or
engineering a stable association between a
nitrogen-fixing bacterium and a cereal crops has
remained elusive:
– Requires simultaneous transfer of 9-20 genes, most of
which are essential.
– Very fragile system with activity being lost quickly
when the expression of any gene is suboptimal.
26. Conti…
• Successful transfer of
nitrogen fixation to the
facultative anaerobe
E.coli by refactoring
nitrogen fixation
cassettes.
Most microbes that
efficiently colonize
plants as associative
bacteria or endophytes
are aerobic organisms.
• Challenge of
transferring to aerobic
microorganisms :
nitrogenase is oxygen
labile.
Some aerobes(Azotobactor
vinelandii, Azorhizobium
caulinodans) : capable of
free-living nitrogen
fixation.
27. Summary
Symbiotic
microorganisms are
intimate allies of
plants
These symbioses are
mutualistic
associations in which
both partners benefit
The plant uses a
core SYM pathway
for symbioses with
mycorrhizal fungi and
rhizobia
