defense mechanism of plant

1. How Plants Defend Themselves Against Pathogens

2. HOW PLANTS DEFEND
THEMSELVES AGAINST
PATHOGENS
Each plant species is affected by approximately one
hundred different kinds of fungi , bacteria ,
mycoplasmas , Viruses , and nemotodes .
a single plant is attacked by hundreds , thousands . and
in the leaf spot diseases of large trees ,probably
hundreds of thousands of individuals of a single kind of
pathogen .
Such plants may suffer damage to a lesser or greater
extent , many survive all these attacks and . not
uncommonly, manage to grow well and to provide
appreciably yields .

3. In general , plants defend themselves
against pathogens by a combination of
weapons from two arsenals :
( 1 ) Structural characteristics act as
physical barriers and inhibit the
pathogen from gaining entrance and
spreading through the plant ,
(2) Biochemical or physiological
characteristics

5. Structural Characteristics
Preexisting structures

7. WAX and CUTICLE
In addition to its function as a permeability
barrier for water and other molecules (prevent
water loss), the micro and nano-structure of
the cuticle have specialised surface properties
that prevent contamination of plant tissues
with external water, dirt and microorganisms

8. A plant’s first line of defense against pathogens is
ultra structure section surface , which the pathogen
must penetrate if it is to cause infection .
Some structural defenses are present in the plant
even before the pathogen comes in contact with the
plant.
Such structures include the amount and quality of
wax and cuticle that cover the epidermal cells , the
structure of the epidermal cell walls , the size ,
location , and shapes of stomata and lenticels , and
the presence on the plant of tissues made of thick-
walled cells that hinder the advance of the pathogen .

10. Waxes on leaf and fruit surfaces form a water-
repellent surface and thereby prevent the
formation of a film of water on which
pathogens might be deposited and germinate
(fungi) or multiply (bacteria) . A thick mat of
hairs on a plant surface may also exert a
similar water-repelling effect and may reduce
infection.

13. A thick cuticle may increase resistance
to infection in diseases in which the
pathogen enters its host only through
direct penetration . Cuticle thickness ,
however , is not always correlated with
resistance , and many plant varieties
with cuticle of considerable thickness
are easily invaded by directly
penetrating pathogens .

14. STOMATA
Stomata are typically found in plant leaves but
can also be found in some stems. Specialized
cells known as guard cells surround stomata
and function to open and close stomatal pores.
Stomata allow a plant to take in carbon dioxide,
which is needed for photosynthesis

15. Many pathogenic fungi and bacteria enter plants only
through stomata .
Although the majority of pathogens can force their
way through closed stomata , some , like the stem
rust of wheat , can enter only when stomata are open
.
Thus , some wheat varieties in which the stomata
open late in the day , are resistant because the germ
tubes of spores germinating in the night dew
desiccate owing to evaporation of the before the
stomata begin to open .
the structure of the stomata – for example , a very
narrow entrance and broad , elevated guard cell –
may also confer resistance to some varieties against
certain of their pathogens .

18. Trichomes
The non-glandular trichomes develop to form a
thick and dense surface around the leaves
which serves to protect leaves and the plant in
general from harsh environmental conditions
as well as protection from pathogens. With
some plants such as Tragia cannabina stinging
hairs develop to protect the plant from
herbivores.

22. LENTICEL
In plant bodies that produce secondary growth,
lenticels promote gas exchange of oxygen,
carbon dioxide, and water vapor. ... In woody
plants, lenticels commonly appear as rough,
cork-like structures on young branches.
Underneath them, porous tissue creates a
number of large intercellular spaces between
cells.

26. HYDATHODES
The structure and function of hydathode in
Arabidopsis. Hydathodes are the structures
that discharge water from the interior of the
leaf to its surface in a process called guttation.
... It is thought that guttation is a necessary
process to absorb solutes when transpiration
is suppressed.

27. Hydathodes in plants

28. Disease and injury are not the same :
The disease is not the result of tissue removal .
However , one should not ignore the
tremendous wound sites produced by tissue
removal and their potential for entry sites for
opportunistic parasites that may lead to
disease .

30. The function of cork layer plant defense
It can be found in underground plant organs,
as an above-ground tissue of woody species
(cork), and as a wound-healing tissue. Its outer
layers are composed of phellem cells with
suberized walls that constitute a protective
barrier, preventing pathogen invasion and fluid
loss.

33. ABSCISSION LAYER
A plant will abscise a part either to discard a
member that is no longer necessary, such as a
leaf during autumn, or a flower following
fertilisation, or for the purposes of
reproduction. ... Abscission can also occur in
premature leaves as a means of plant defense.

35. TYLOSES
Tyloses occur widely among plant species, and
are induced by environmental stimuli such as
wounding and pathogen infection. Tyloses
impair xylem function by blocking vessels, but
they are also a component in wound healing
and may inhibit the intrusion and spread of
pathogens.

39. Biochemical or Physiological
chracteristics
The combinations of structural
characteristics and biochemical re actions
employed in the defense of plants are
different in different host – pathogen
systems. In addition, even within the same
host and pathogen, the combinations very
with the age of the plant. The kind of plant
organ and tissue attacked the nutritional
condition of the plant, and with the weather
conditions .

40. Hypersensitive Response :
Pathogen produced elicitor binds to host elicitor binding site.
Recognition and activation of defense responses .
Defense response triggered to kill infected hos cell.
Kill pathogen before further spread .
Kill pathogen via buildup of toxic compounds in infected cell .

44. Elicitors found in the apoplastic space. Plant cell surface
receptors recognize a variety of pathogen-derived microbe-
associated molecular patterns (MAMPs) and plant-derived
damage-associated molecular patterns (DAMPs) as an initial
step in the induction of the immune response. Molecules from
bacteria (shown in yellow), fungi (orange), and oomycetes
(pink) all act as triggers for plant immunity after direct
interaction with pattern recognition receptors (PRRs). The
invasion of pathogens also results in the release of plant
molecules (green) that are not otherwise present in the
apoplast, which provides a danger signal to the host. The
known receptors of these molecules are grouped based on the
nature of their ligand-binding domains. Regardless of the signal,
these binding events lead to intracellular signaling and
ultimately an immune response designed to control and
eliminate the infection.

45. Inducible Chemical Defenses of
the Plant
Identifying the Intruder – Perception of Exogenous Molecules
Microbe-associated molecular pattern perception is the
dominant means by which apoplestic pathogens are
recognized and PTI elicited. MAMPs are regions of highly
conserved microbe-derived molecules that are recognized by
host PRRs, and are therefore broadly analogous to immune
epitopes. A wide range of MAMPs have been described from
fungal, oomycete, and bacterial pathogens, which span
molecular classes including oligosaccharides, lipids, and
peptides.

46. Regardless of their source and nature, these molecular
signatures provide a signal of potential pathogen attack to
the host. Some MAMPs are perceived across large swaths
of the plant kingdom, while perception of others is more
phylogenetically restricted (Boller and Felix, 2009). Overall,
MAMP-induced PTI plays a critical role in the control of
pathogen success and has enormous potential to influence
crop disease resistance and productivity. Meanwhile, the
protection afforded to the plant through these epitopes
provides a strong evolutionary pressure on the pathogen to
avoid this recognition, resulting in numerous pathogenic
strategies to avoid MAMP-perception.