Plants have array of defense response against biotic stresses which could be either structural reinforcement, release of chemicals, and defense gene expression against invading organisms. The physical barriers are trichoms, waxy cuticle, thick cell wall. Once the pathogen overcomes the first line of defense, basal or innate defense response comes into play. Pathogens secrete some conserved molecules known as Pathogen Associated Molecular Pattern (PAMP/MAMP), which are recognized by transmembrane receptors present in the plasma membrane and initiate a series of signal cascade reaction which ultimately leads to activation of various defense related genes. Apart from inducing the expression of defense related genes, it also triggers a hypersensitive reaction (HR) which cause deliberate cell death at the site of infection and limit the pathogen access to water and nutrient by sacrificing a few cells in order to save the rest of the plant. Once HR is triggered, plant tissue may become highly resistant to a broad range of pathogens for an extended period of time. This phenomenon is called Systemic Acquired Resistance (SAR).
Plants respond to herbivory is a similar manner as described above. The biochemical mechanisms of defense against the herbivores are wide-ranging, highly dynamic, and are mediated both by direct and indirect defenses. The defensive compounds are either produced constitutively or in response to plant damage, and affect feeding, growth, and survival of herbivores. In addition, plants also release volatile organic compounds that attract the natural enemies of the herbivores. These strategies either act independently or in conjunction with each other. However, our understanding of these defensive mechanisms is still limited. Induced resistance could be exploited as an important tool for the pest management to minimize the amounts of insecticides used for pest control. Host plant resistance to insects, particularly, induced resistance, can also be manipulated with the use of chemical elicitors of secondary metabolites, which confer resistance to insects. By understanding the mechanisms of induced resistance, we can predict the herbivores that are likely to be affected by inducing responses. The elicitors of induced responses can be sprayed on crop plants to build up the natural defense system against damage caused by herbivores. The induced responses can also be genetically engineered, so that the defensive compounds are constitutively produced in plants challenged by the herbivory. Induced resistance can be exploited for developing crop cultivars, which readily produce the inducible response upon mild infestation, and can act as one of components of integrated pest management for sustainable crop production.
Molecular basis of plant resistance and defense responses to pathogensSenthil Natesan
In response to pathogen attack, plants have evolved sophisticated defense mechanisms to delay or arrest pathogen growth.Unlike animals, plants lack a circulating immune system recognizing microbial pathogens. Plant cells are more autonomous in their defense mechanisms and rely on the innate immune capacity of each cell and systemic signals that disseminate from infection sites (Jones and Dangl, 2006). Plant innate immunity consists of preformed physical and chemical barriers (such as leaf hairs, rigid cell walls, pre-existing antimicrobial compounds) and induced defenses. Should an invading microbe successfully breach the pre-formed barriers, it may be recognized by the plant, resulting in the activation of cellular defense responses that stop or restrict further development of the invader.
Plants have array of defense response against biotic stresses which could be either structural reinforcement, release of chemicals, and defense gene expression against invading organisms. The physical barriers are trichoms, waxy cuticle, thick cell wall. Once the pathogen overcomes the first line of defense, basal or innate defense response comes into play. Pathogens secrete some conserved molecules known as Pathogen Associated Molecular Pattern (PAMP/MAMP), which are recognized by transmembrane receptors present in the plasma membrane and initiate a series of signal cascade reaction which ultimately leads to activation of various defense related genes. Apart from inducing the expression of defense related genes, it also triggers a hypersensitive reaction (HR) which cause deliberate cell death at the site of infection and limit the pathogen access to water and nutrient by sacrificing a few cells in order to save the rest of the plant. Once HR is triggered, plant tissue may become highly resistant to a broad range of pathogens for an extended period of time. This phenomenon is called Systemic Acquired Resistance (SAR).
Plants respond to herbivory is a similar manner as described above. The biochemical mechanisms of defense against the herbivores are wide-ranging, highly dynamic, and are mediated both by direct and indirect defenses. The defensive compounds are either produced constitutively or in response to plant damage, and affect feeding, growth, and survival of herbivores. In addition, plants also release volatile organic compounds that attract the natural enemies of the herbivores. These strategies either act independently or in conjunction with each other. However, our understanding of these defensive mechanisms is still limited. Induced resistance could be exploited as an important tool for the pest management to minimize the amounts of insecticides used for pest control. Host plant resistance to insects, particularly, induced resistance, can also be manipulated with the use of chemical elicitors of secondary metabolites, which confer resistance to insects. By understanding the mechanisms of induced resistance, we can predict the herbivores that are likely to be affected by inducing responses. The elicitors of induced responses can be sprayed on crop plants to build up the natural defense system against damage caused by herbivores. The induced responses can also be genetically engineered, so that the defensive compounds are constitutively produced in plants challenged by the herbivory. Induced resistance can be exploited for developing crop cultivars, which readily produce the inducible response upon mild infestation, and can act as one of components of integrated pest management for sustainable crop production.
Molecular basis of plant resistance and defense responses to pathogensSenthil Natesan
In response to pathogen attack, plants have evolved sophisticated defense mechanisms to delay or arrest pathogen growth.Unlike animals, plants lack a circulating immune system recognizing microbial pathogens. Plant cells are more autonomous in their defense mechanisms and rely on the innate immune capacity of each cell and systemic signals that disseminate from infection sites (Jones and Dangl, 2006). Plant innate immunity consists of preformed physical and chemical barriers (such as leaf hairs, rigid cell walls, pre-existing antimicrobial compounds) and induced defenses. Should an invading microbe successfully breach the pre-formed barriers, it may be recognized by the plant, resulting in the activation of cellular defense responses that stop or restrict further development of the invader.
this presentation provides an idea on how plants act when they are infected by a pathogen.specially post infection structural mechanisms of plants have been discussed.
Systemic Acquired Resistance (SAR) and it’s Significance in Plant Disease Ma...Ankit Chaudhari
Systemic Acquired Resistance (SAR) is a mechanism of induced defense that confers long-lasting protection against a broad spectrum of microorganisms and pests. Presently disease control is largely based on the use of hazardous chemicals viz., fungicides, bactericides and insecticides for either direct or indirect disease management. The hazardous natures of the products on the environment, human and animal health strongly necessitates the search for new safer means of disease control. SAR have high potential to diminish the use of toxic chemicals in the agriculture and has emerged as an alternative, non-conventional, non-biocidal and eco-friendly approach for plant protection and hence for sustainable agriculture. SAR requires the signal molecule salicylic acid (SA) and is associated with accumulation of pathogenesis-related proteins, which are thought to contribute to resistance.
Gene for gene system in plant fungus interactionVinod Upadhyay
MOLECULAR CHARACTERIZATION OF GENE FOR GENE SYSTEMS IN PLANT- FUNGUS INTERACTION AND THE APPLICATIONS OF AVIRULENCE GENES IN CONTROL OF PLANT PATHOGENS
plant pathogen interaction
different types of pathogens
gene for gene hypothesis
direct receptor model
Elicitor receptor model
suppersor repressor model
gaurd hypothesis
The concept of gene for gene hypothesis was first developed by Flor in 1956 based on his studies of host pathogen interaction in flax, for rust caused by Melampsora lini. The gene for gene hypothesis states that for each gene controlling resistance in the host, there is corresponding gene controlling pathogenicity in the pathogen. The resistance of host is governed by dominant genes and virulence of pathogen by recessive genes. The genotype of host and pathogen determine the disease reaction. When genes in host and pathogen match for all loci, then only the host will show susceptible reaction. If some gene loci remain unmatched, the host will show resistant reaction. Now gene – for –gene relationship has been reported in several other crops like potato, sorghum, wheat, etc. The gene for gene hypothesis is also known as “Flor Hypothesis.”
this presentation provides an idea on how plants act when they are infected by a pathogen.specially post infection structural mechanisms of plants have been discussed.
Systemic Acquired Resistance (SAR) and it’s Significance in Plant Disease Ma...Ankit Chaudhari
Systemic Acquired Resistance (SAR) is a mechanism of induced defense that confers long-lasting protection against a broad spectrum of microorganisms and pests. Presently disease control is largely based on the use of hazardous chemicals viz., fungicides, bactericides and insecticides for either direct or indirect disease management. The hazardous natures of the products on the environment, human and animal health strongly necessitates the search for new safer means of disease control. SAR have high potential to diminish the use of toxic chemicals in the agriculture and has emerged as an alternative, non-conventional, non-biocidal and eco-friendly approach for plant protection and hence for sustainable agriculture. SAR requires the signal molecule salicylic acid (SA) and is associated with accumulation of pathogenesis-related proteins, which are thought to contribute to resistance.
Gene for gene system in plant fungus interactionVinod Upadhyay
MOLECULAR CHARACTERIZATION OF GENE FOR GENE SYSTEMS IN PLANT- FUNGUS INTERACTION AND THE APPLICATIONS OF AVIRULENCE GENES IN CONTROL OF PLANT PATHOGENS
plant pathogen interaction
different types of pathogens
gene for gene hypothesis
direct receptor model
Elicitor receptor model
suppersor repressor model
gaurd hypothesis
The concept of gene for gene hypothesis was first developed by Flor in 1956 based on his studies of host pathogen interaction in flax, for rust caused by Melampsora lini. The gene for gene hypothesis states that for each gene controlling resistance in the host, there is corresponding gene controlling pathogenicity in the pathogen. The resistance of host is governed by dominant genes and virulence of pathogen by recessive genes. The genotype of host and pathogen determine the disease reaction. When genes in host and pathogen match for all loci, then only the host will show susceptible reaction. If some gene loci remain unmatched, the host will show resistant reaction. Now gene – for –gene relationship has been reported in several other crops like potato, sorghum, wheat, etc. The gene for gene hypothesis is also known as “Flor Hypothesis.”
Defensive mechanisms in Plants: The role of component plant cells in defense ...Agriculture Journal IJOEAR
— Plants are often exposed to various environmental stresses such as extreme temperatures, drought, and disease and pest attack. In natural systems, plants face a plethora of antagonists and thus posses a myriad of defense and have evolved multiple defense mechanisms by which they are able to cope with various kinds of biotic and abiotic stresses. In fact plants defense against stresses by different ways. The role of cellular organelles is very important in this way. Cell wall and their derivatives such as oligosaccharins as biochemical defenser or for example trichomes as mechanical defenser is the frontline of the plant defense system. Also Plants have evolved a multi-layered immune system that dynamically responds to pathogens alike cell membrane that is a key mediator of communication between plants and microbes. Cytoplasm and the membrane-bounded structures (organelles) defense against different kind of stresses. The role of cellular organelles in plant defense relate to their enzymes primarily. Enzymes such as proteases, esterases and ribonucleases in cytoplasm, PM H+-ATPases in plasma membrane or β glucosidases included cyanogenic glucosides, saponins, glucosinolates or DIMBOA (2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one) glucoside in ER are responsible for plant defense. Also ROSs plus SA and JA in chloroplast and mitochondria play an important role in immune plant system. In nucleus macromolecules including nucleoporins, importins, and Ran-GTP-related components, are essential to mount an efficient immune response in response to different pathogens. And in Golgi apparatus, peroxysomes and vacuoles, glycosyltransferases, myrosinase and hydrolytic enzymes are liable for plant defense respectively. Keywords— biotic and abiotic stresses; organells; plant defense.
a detailed description of structural and biochemical mechanisms and importance of phytoalexins in plants and different types of phytoalexins produced the plants and its functions and importance in plant defense mechanism
Detailed description on the mode of actions of various phytoalexins, mechanisms involved phtyoalexin formation, various types of phytoalexins, its functions
Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
What is greenhouse gasses and how many gasses are there to affect the Earth.moosaasad1975
What are greenhouse gasses how they affect the earth and its environment what is the future of the environment and earth how the weather and the climate effects.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
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.
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.
Comparing Evolved Extractive Text Summary Scores of Bidirectional Encoder Rep...University of Maribor
Slides from:
11th International Conference on Electrical, Electronics and Computer Engineering (IcETRAN), Niš, 3-6 June 2024
Track: Artificial Intelligence
https://www.etran.rs/2024/en/home-english/
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.
2. RESISTANCE
The ability of an organism to exclude or overcome completely
or in some degree, the effect of a pathogen, or other damaging
factor.
Non-Host Resistance
Plants are resistant to certain pathogen either because they
belong to taxonomic groups that are outside the host range of
these pathogens.
Gene For Resistance
They posses gene for resistance (R gene) directed against the
gene for virulence of the pathogen.
INTRODUCTIO
N
3. TRUE RESISTANCE
Disease resistance that is genetically controlled by the presence
of one, a few or many genes for resistance in the plants is known
as True resistance.
In true resistance the host and the pathogen are more or less
incompatible with one another either because of the lack of the
chemical recognition between the host and the pathogen.
TYPES
1. Horizontal resistance
2. Vertical resistance
4. 1. Horizontal resistance
Such resistance is also called non-specific, general, quantitative,
adult plants, field or durable resistance but it is most commonly
known as horizontal resistance.
Horizontal resistance is controlled by many type of genes so it is
also called Polygenic resistance.
2. Vertical resistance
Such resistance is also called strong, major, specific, qualitative
or differential resistance but it is most commonly known as
vertical resistance.
Vertical resistance is always controlled by one gene so it is also
called monogenic resistance.
5. APPARENT RESISTANCE
In any area, and almost every year, limited or widespread plant
disease epidemics occur on various crop plants.
The apparent resistance to disease of plants known to be
susceptible is generally the result of disease escape or tolerance to
disease.
DISEASE ESCAPE
Disease escape occurs whenever genetically susceptible plants do
not become infected because the three factor necessary for disease
do not coincide.
1.Susceptible host
2.Virulent pathogen
3.Favourable environment
6. PREEXISTING STRUCTURAL AND CHEMICAL DEFENSES
Preexisting structural defense
Wax
Thick cuticle
Thickness and toughness of the outer wall of epidermal cells
Stomata
Sclerenchyma cells
Lenticel
Preexisting chemical defense
1. Inhibitors
Released by plant in it’s environment
Present in plant cells before infection
2. Phenolics
Tannins
Glucanases
Dienes
Chitinase
7. INDUCED STRUCTURAL AND CHEMICAL DEFENSES
Induced structural defense
Cytoplasmic defense reaction
Cell wall defense structure
Histological defense structure
Formation of cork layer
Formation of abscission layer
Formation of tyloses
Deposition of gums
Induced chemical defense
Hypersensitivity response (HR)
Production of Antimicrobial substances
Pathogenesis- Related Protein (PR Protein)
Phytoalexins
Systemic acquired Resistance
8. PREEXISTING STRUCTURAL DEFENSE
Some structural defense are present in the plant even before the
pathogen comes in contact with the plant.
1. WAXES
Waxes is a general term used to the mixture of long-chain
apolar lipids forming a protective coating (cutin in the
cuticle) on plant leaves and fruits
Synthesized by epidermal cells
Extremely hydrophobic
Waxes form outer coating of the cuticle
Often crystallizes in pattern of rods, tubes or plates
9. 2. THICK CUTICLE
Plant cuticle are protective, hydrophobic, waxy covering
produced by the epidermal cells of leaves, young shoots and all
other aerial plant organ.
Thickness of cuticle e.g. in resistant flax Melampsora lini,
Barberry-Puccinia graminis tritici
10. 3.THICKNESS AND TOUGHNESS OF THE OUTER WALL
OF EPIDERMAL CELLS
The thickness and toughness of outer wall of epidermal cells are
apparently important factors in the resistance of some plants to
certain pathogen.
Thick, tough walls of epidermal cells make direct penetration by
fungal pathogens difficult or impossible.
For example Barberry- Puccinia graminis tritici resistance is
attributed to the tough outer epidermal cells.
4.STOMATA
The minute pores in the epidermis of leaf through which
exchange of gases takes place.
Size of stomata (Resistant citrus vars. have small stomata-
Xanthomonas campestris)
Location and shape of stomata, opening and closing (resistant
wheat vars. – Rust).
11. 5. SCLERENCHYMA CELLS
Composed of walls thickened with lignin
Have brittle cells helps in mechanical support to plants
These cells effectively blocks spread of fungal and bacterial
pathogen that cause angular leaf spot
For example some wheat varieties resistant to stem rust-stem
contain high sclerenchyma cells.
6. LENTICEL
Lenticels are airy cells in the bark of stem and roots
The shape and internal structure of lenticels can increase and
decrease the incidence of fruit disease
Lenticels of small size restrict entry of pathogen.
12. PREEXISTING CHEMICAL DEFENCE:
Although structural characteristics may provide a plant with
various degree of defence against attacking pathogens.
It is clear that the resistance of a plant against pathogen attack
depends not so much on its structural barriers as on the substances
produced in its cell before or after infection.
INHIBITORS RELEASED BY THE PLANT IN IT’S
ENVIRONMENT
Plants exude a variety of substances through the surface of their
aboveground parts as well as through the surface of their roots.
Fungitoxic exudates- on the leaves of some plants, e.g. tomato and
sugarbeet inhibit the germination of Botrytis and Cercospora
Oil capric acid on elm seed toxic to Ceratocystis ulmi spores
Phenolics: red scale onion against smudge –Colletotrichum
circinans
14. INHIBITORS PRESENT IN PLANT CELLS BEFORE
INFECTION
It is becoming increasingly apparent that some plants are
resistant to disease caused by certain pathogen of an inhibitory
compound present in the cell before infection.
Stored in vacuoles, lysogenous glands, heart wood periderm
of plants
Phenolics – onion (catechol and protocatechuic acid )
Saponins (tomatin in tomato, avenacin in oats ) most of these
compounds inhibits hydrolytic enzymes produced by pathogen
e.g. pectolytic enzymes etc.
Tannins, and some fatty acid-like compound such as dienes,
which are present in high concentrations in cells of young
fruits, leaves or seeds.
Some plants also contains hydrolytic enzymes e.g.
glucanases, chitinases etc.
15. INDUCED STRUCTURAL AND CHEMICAL DEFENSES
INDUCED STRUCTURAL DEFENSE
Cytoplasmic Defense Reaction
Some of the defense structures formed involve the cytoplasm of the cells
under attack, and the process is called cytoplasmic defense reaction.
Cell Wall Defense Structure
It involve morphological changes in the cell wall or change derived from
the cell wall of the cell being invaded by the pathogen.
Three main types of such structures have been observed in plant diseases.
The outer layer of the cell wall of parenchyma cells coming in contact with
incompatible bacteria swells and produced an amorphous, fibrillar material
that surrounds and traps the bacteria and prevents them from multiplying.
Cell walls thicken in response to several pathogens by producing what
appears to be a cellulosic material.
Callose papillae are deposited on the inner side of cell walls in response to
invasion by fungal pathogen.
16. Histological Defense Structures
Formation Of Cork And Abscission Layer
The formation of cork or abscission layers can limit the size of lesions, and
consequently the extent of damage that can be caused by a single
infection.
e.g. Cork layer Rhizoctonia solani canker in potato
Abscission layer Xanthomonas pruni shot hole
Provide protection by -
Inhibiting the further
spread of pathogen
Block the spread of
toxic substances of the
pathogen
stop the flow of
nutrients to infection
point
17. Tyloses
Tyloses are overgrowth of living cells that protrude via pits into
xylem vessels blocking the vascular system.
If they form abundantly and quickly, they can stop the spread of
vascular wilt pathogens.
Their formation is triggered by a “stress condition”.
18. DEPOSITION OF GUM
Various types of gums are produced by many plants
around lesions after infection by pathogen or injury.
Gums secretion is most common in stone fruit trees but
occurs in most plants.
Generally these gums are exudated by plant due to the
stressed condition.
The production gum by these trees by the process
called as gummosis.
19. INDUCED CHEMICAL DEFENSE
HYPERSENSITIVE RESPONSE (HR)
The hypersensitive response is localized death of host cells at
the site of infection.
It is the result of a specific recognition of a pathogen attack by
the host.
The HR is considered to be a type of programmed cell death.
20. The hypersensitive response is the culumination of the plant
defense response initiated by:
The recognition by the plant of specific pathogen-produced
signal molecules, known as elicitors.
Recognition of the elicitors by the host plant activates a cascade
of biochemical reactions in the attacked and surrounding plant
cells, leads to new or altered cell functions and to new or greatly
activated defense- defense related compounds.
The most common new cell functions and compound include:
A rapid burst of reactive oxygen species, leading to a dramatic
increase of oxidative reaction.
Increased ion movement, especially of K+ and H+ through the
cell membrane.
21. PRODUCTION OF ANTIMICROBIAL SUBSTANCES
PATHOGENESIS- RELATED PROTEINS (PR-
PROTEINS)
Pathogenesis related proteins, called PR- proteins- A group of
plant coded proteins
Are structurally diverse group toxic to invading pathogens.
Produced under stress
They are widely distributed in plants in trace amounts but are
produced in high concentration following pathogen attack or
stress.
The PR proteins exist in plant cells intracellularly (acidic in
Apoplast & basic form in vacuoles) and also in the intercellular
spaces.
Varying types of PR- proteins have been isolated from several
crop plants.
22. Groups of PR- proteins
The better known PR protein are:
PR- 1 proteins, B-1,3-glucanases, chitinases, lysozymes
PR 4 proteins, thaumatinelike proteins, osmotinlike
proteins, cysteine-rich proteins, glycine-rich proteins,
proteinase inhibitors, proteinases and peroxidases. There
are often numerous isoforms of each PR- protein in
various host plants.
23. PHYTOALEXINS
Concept given by Borger & Muller in Potato- late blight
interactions
Defined as antibiotics produced in plant- pathogen interaction or
as a response to injury or physiological stimuli
Paxton (1981) defined phytoalexins as low molecular weight
antimicrobial compounds which are synthesized by and
accumulates in plant cells after microbial infection.
Involves the role of elicitors in their production
Not produced during bio trophic infection.
E.g. Leguminosae, Solanaceae, Malvaceae, Graminae,
Compositae, Umbelliferae and Chenopodiaceae.
24. SYSTEMIC ACQUIRED RESISTANCE (SAR)
SAR confers broad-based resistance to different pathogens.
For example, primary inoculation with a fungal leaf spot
pathogen reduces susceptibility of the host plant to other fungi
as well as to bacterial and viral pathogens.
Salicylic acid (chemical related to aspirin) is part of signaling
pathway involved in transmission of the defense response
throughout the plant to produce SAR. This has lead to the
development of synthetic chemicals that mimic the role of
salicylic acid.
25. Induction of Systemic Acquired Resistance
Production of H2O2 (plus antioxidants)
Hydrogen peroxide has been associated
secondary induction of SAR and direct toxic
activity to invading pathogens
Thickening of plant cell wall Production of
phenolic (lignin, tannic acid) that strengthen
walls and inhibit pathogen enzymes
Accumulation of pathogenesis related
proteins “PR-proteins” chitinases, ß-1,3
Glucanases.
These enzymes accumulate in vacuole of
plant cell. Upon attack, they directly degrade
fungal cell walls. Indirectly, their action
results in the release of fungal wall
components that elicit additional defense
reactions
Sprayed
inducer
(activator) that
mimics
salicyclic acid
26. CONCLUSION
Under favourable condition the infection(susceptibility) or non-
infection (resistance) in each host-pathogen combination is
predetermined by the genetic material of the host and of the
pathogen.
In some diseases however, particularly those caused by fungi,
such as potato late blight, apple scab, powdery mildews, tomato
leaf mould, and the cereal smuts and rust, and also in several
viral and bacterial disease of plants, considerable information
regarding the genetics of host-pathogen interaction is available.