Transcript plant immunology lecture 5,6

PLANT IMMUNOLOGY
Lecture 5, 6
PLANT CELL
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The cell is the basic unit of life.
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Plant cells are eukaryotic cells or cells with membrane bound
nucleus.
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Generally, plant cells are larger than animal cells and are mostly
similar in size and are rectangular or cube shaped.
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Plant cells are similar to animal cells in being eukaryotic and they
have similar cell organelles.
COMPONENTS OF PLANT CELL
COMPONENTS OF PLANT CELL
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Outer-layer of cell is composed of:
 Cell wall
 Plasma membrane
 Plasmodesmata
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Inside the cell, it has following components:
 Cytoplasm
 Cell nucleus
 Vacuole
 Nucleolus
 Nuclear membrane
 Ribosomes





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Rough endoplasmic reticulum
Smooth endoplasmic reticulum
Mitochondrian
Chloroplast
Golgi body
Microtubules
CELL WALL
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Plant cells have cell walls. The most
composition of a plant cell wall is cellulose.
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Long cellulose molecules grouped into bundles called microfibrils
are twisted into rope-like macrofibrils.
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Sometimes there is also another layer component of cell wall e.g
lignin - which gives strength, e.g. strengthens wood (xylem cells)
in trees.
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suberin - which helps prevent water from penetrating, e.g. suberin
in mangroves minimize salt intake from their habitat
important
chemical
FUNCTION(S) OF PLANT CELL WALLS
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The main functions of plant cell walls are mechanical.
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Plant cell walls form part of a transport system called the
apoplast system via which water and some solutes can pass
through plant tissue via
 apoplastic pathways (along / through cell walls)
 symplastic pathways (i.e. through the cytoplasm of a series of
adjacent cells).
PLASMA MEMBRANE
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The plasma membrane is flexible enough to move closer to or
away from the cell wall - according to changes in the water
content of the cytoplasm within the cell.
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As a differentially-permeable surface, the plasma membrane
controls movement of solutes in and out of the cell.
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Synthesis and assembly of cell wall components
PLASMODESMATA
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Plasmodesmata are tiny strands of cytoplasm that pass through
pores in plant cell walls, forming "connections" or "pathways"
between adjacent cells.
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Specifically, plasmodesmata form the symplast pathway for the
movement of water and solutes through plant structures.
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These cell-cell connections are especially important for the
survival of plant cells during conditions of drought.
CYTOPLASM
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The cytoplasm is the part of a plant cell that includes all the contents of
the cell within the cell membrane but outside of the nucleus of the cell.
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It therefore includes the cytosol (i.e. the semi-fluid part of a cell's
cytoplasm) as well as the plant cell organelles incl. mitochondria,
chloroplasts, etc..
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Also located within the cytoplasm is the cytoskeleton, which is a
network of fibres whose function is to provide mechanical support to the
cell, including helping to maintain the cell's shape.
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Cytoplasm consists mainly of water and contains enzymes, salts,
organelles, and various organic molecules.
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It has a clear appearance and a gel-like texture.
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The cytoplasm helps to move materials around the cell and also
dissolves cellular waste
VACUOLE
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A cell's vacuole can occupy a large proportion of the total volume of the
cell - e.g. 90% of the volume of some mature plant cells.
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Each vacuole is enclosed by a vacuolar membrane called the tonoplast.
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Contents of the vacuole:
 cell sap, which is a solution of salts, sugars and organic acids.
 Enzymes needed for recycling components of cells, e.g. chloroplasts.
 Anthocyanins are sometimes present in cell vacuoles. These are
chemical pigments responsible for some of the (non-green) colours of
glowers, e.g. reds, blues, purples.
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Helps maintain turgor pressure (turgidity) inside the cell. This pressure
pushes the plasma membrane against the cell wall. Plants need turgidity
to maintain rigidity.
CELL NUCLEUS
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The nucleus is the "control center" of a eukaryotic cell (i.e. plant
cells and animal cells)
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Each cell nucleus is surrounded by a nuclear membrane that is
also known as the "nuclear envelope".
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The contents of the nucleus - so, inside the nuclear membrane includes DNA (genetic material) in the form of genes and a
nucleolus.
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The cell nucleus controls the activity of the cell by regulating
protein synthesis within the cell.
NUCLEOLUS & NUCLEAR MEMBRANE
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The nucleolus is located within the nucleus and is the site of
synthesis of:
 Transfer RNA
 ribosomal RNA
 ribosomal subunits
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The nuclear membrane is also known as the nuclear envelope and
encloses the contents of the nucleus of the cell - separating the
contents of the nucleus from the rest of the cell.
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Nuclear pores in the nuclear membrane enable various
substances, such as nutrients and waste products, to pass into and
out of the nucleus.
ENDOPLASMIC RETICULUM
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Rough endoplasmic reticulum is the site of protein synthesis
(which takes place within the ribosomes attached to the surface of
the RER) as well as storage of proteins and preparation for
secretion of those proteins.
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Smooth endoplasmic reticulum is the site of lipid synthesis and
secretion within cells
MITOCHONDRIAN
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Mitochondria are structures found in both plant and animal cells.
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They are bounded by double membranes, the inner of which is
folded inwards, forming projections (called cristae).
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Their function of mitochondria is energy production.
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Mitochondria contain enzyme systems needed to synthesize
adenosine triphosphate (ATP) by oxidative phosphorylation.
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The quantity of mitochondria within cells varies with the type of cell.
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In the case of plant cells, mitochondria may be particularly abundant
in sieve tube cells (also called sieve tube members), root epidermal
cells and dividing meristematic cells.
CHLOROPLASTS
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Chloroplasts are the sites of photosynthesis within plant cells.
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Chloroplasts are very important parts of plant cells.
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Some cells include up to 50 chloroplasts.
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The number of chloroplasts per cell varies according to the type of
cell and its function.
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They are plentiful in leaf cells that receive sunlight - as opposed to
root cells that do not receive light.
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Chloroplasts are a type of plastid. There are also other types of
plastids (not all of which are present in all plant cells but all of
which are derived from proplastids.
GOLGI APPARATUS
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The Golgi apparatus of a cell is sometimes called the "packaging
organelle" because it plays a role in transporting proteins.
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It's structure and appearance takes the form of a stack of tiny
pancake-like shapes, each of which is enclosed by a single
membrane and contains fluid and biochemicals such as proteins,
sugars and enzyme.
FUNCTIONS OF GOLGI APPARATUS
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Modifies some newly-synthesized biomolecules before storing them in
granules, sometimes called vesicles - ready for transport later.
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Forms lysosomes - which are tiny sacs filled with enzymes that enable the
cell to utilize its nutrients, so are sometimes described as "cell digestion
machines". Lysosomes also destroy the cell after it has died.
• Transports the proteins produced in the ER:
After a
protein has been synthesized in the ER, a transition vesicle (or "sac") is
formed then floats through the cytoplasm to the Golgi apparatus, into
which it is absorbed.
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After processing the molecules inside the sac, a secretory vesicle is formed
and released into the cytoplasm, moves to the cell membrane, then
releases the molecules from the cell
MICROTUBULES
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Microtubules are hollow rope-like structures composed of the
protein Tubulin .
They can be as long* as 25μm and have a diameter of approx 25
nm.
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Functions
 facilitate addition of cellulose to cell wall
 form the spindles and cell plates of dividing cells
 play a role in cytoplasmic streaming (i.e. moving the fluid
cytoplasm within the cell) e.g. to/from chloroplasts.
RIBOSOMES
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Ribosomes take part in the synthesis of some proteins by
catalyzing the formation of those proteins from individual amino
acids (using messenger RNA as a template).
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Examples of proteins catalyzed by ribosomes include
glycoproteins, lysosome proteins, membrane proteins and some
organelle proteins.
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In general, ribosomes can be either "free" or "membrane-bound",
which in the cases of plant and animal cells means attached to the
rough endoplasmic reticulum (RER).
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An individual ribosome could be "membrane-bound" while it is
making one protein, then "free" while making a different protein.
ORGANIZATION OF PLANT TISSUES
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Plants are made up of meristematic and permanent tissues
and are supported by shoot and root organ systems.
The primary plant is made up of 4 tissue types:
Tissue type
Functional roles
meristematic
division of new cells for new growth or repair
ground tissue
bulk tissue; storage, processing, physical support
dermal tissue
protection and sometimes nutrient absorption
vascular tissue
movement of fluids/food and physical support
PLANT ORGANS
• Shoot: stem and leaf
• Node/internode
• Root
• Meristems: Apical & Lateral
PLANT TISSUES
MERISTEMATIC TISSUES
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Meristematic tissues are responsible for the division of new cells...
they are zones of actively dividing cells.
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Cell division occurs solely in
expansion may occur anywhere.
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Thus in a single plant there are zones of young dividing cells,
maturing cells, and mature cells.
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There are 3 meristematic regions in the plant:
 Apical meristems
 Lateral meristem
 Intercalary meristem
meristematic
regions,
while
APICAL MERISTEMS
• Apical meristems are located at the apices or tips - at root
and shoot tips and are directly involved in their elongation
• They create derivatives which form primary growth.
 The protoderm which forms the outer dermal layer of
tissues,
 The ground meristem which forms the cortical cells and
 The procambium which forms the vascular tissue.
ROOT APICAL MERISTEM
LATERAL MERISTEM
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Lateral meristem are responsible for horizontal expansion. It has
following parts:
 Vascular meristem- internal growth in girth which involves
secondary tissues (xylem and phloem). In the fasicular region
the cambial cells which divide toward the center form xylem
tissue and towards the outside phloem tissue.
• Interfasicular indicates the cambium between the 'fasciles of
xylem & phloem.
 Cork cambium- external girth growth beyond the phloem
area.
They
form
the
characteristic
corky
layer
as well as an internal layer.
INTERCALARY MERISTEM
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occurs between mature tissues
sections in the vicinity of the nodes
or leaf attachment.
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common in grasses (occur at bases
of nodes)
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helps regenerate parts removed
(by lawnmowers, herbivores, etc.)
GROUND TISSUES
• Ground Tissue is simple non-meristematic tissue (nondividing tissue) made up 3 cell types:
 Paranenchyma
 Collenchyma
 sclerenchyma.
• This tissue generally forms either the pith, cortex or bulk of
leaf ( mesophyll).
PARENCHYMA CELLS
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Most abundant cells in plants
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Spherical cells which flatten at point of contact; alive at maturity;
pliable, primary cell walls
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large vacuoles for storage of starch, fats, and tannins (denature
proteins)
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Primary sites of the metabolic functions such as photosynthesis,
respiration, and protein synthesis;
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They are "ready reserves" from which a plant makes specialized
cells to meet its changing needs.
COLLENCHYMA CELLS
• Living protoplasm
• Unevenly thickened primary cell walls; elongate cells
• Longer than wide; just beneath epidermis
• Function to support growing organs, grass, floral parts, and
border veins; their non-lignified cell walls can stretch.
SCLERENCHYMA CELLS
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Most are dead at maturity
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Rigid, thick, lignified, nonstretchable secondary cell walls.
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There are 2 types of sclerenchyma cells:
 Sclereids or stone cells- short; variable shape; form hard layers
such as the shells of nuts and seed coats; produce the gritty
texture of pears
 Fibers- long, slender; occur in strands or bundles; tiny cavity or
lumen; the different hardnesses of fibers are used to make
coarse rope, linen cloth, etc.
DERMAL TISSUE
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Epidermal tissue is a single layer of cells, (except in velamen,
pepperomia and rubber plants) that covers the plant body
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Functions:
 Acts as a buffer between the environment and the internal plant
tissues
 Absorption of water and minerals primarily in the root region
 On the stem and leaves generally covered with a cutin which
prevents evaporation, secretion of cuticle (waterproof; made of
cutin= fatty substances)
 Can form a barrier resistant to bacteria and fungi
 Can prevent leaching of materials in or out of the surface
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Leaf hairs (trichomes)- 1-2 cells; important in boundary layer and in
defense; they reflect light to protect against overheating and
excessive water loss.
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This is an incredibly important function for plants in dry regions
where excess light may lead to photobleaching of pigments and
excess absorption of light would overheat the tissue.
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The layer acts to hold in a layer of humidity 'trapped' between the
epidermis and the tips of the trichomes.
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This layer also prevent air moving directly against the stomata
which would encourage water loss. Its' rough surface breaks up
wind currents.
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When in high density they act to deter herbivory by small animals.
STOMATA
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Created by guard cells; most abundant on underside of leaves
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Regulate diffusion of CO2 into the leaf for photosynthesis as well
as regulate loss of water from the leaf
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Stomata respond to turgor pressure
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Stomata open when water enter, thereby increasing turgor
pressure in guard cells, thus pushing them apart
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Stomata close when water leave the guard cells, thus leaving
them flaccid and closing upon each other.
SALT GLANDS
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Dump sites for the excess salt absorbed in water from the soil;
help plants adapt to life in saline environments
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A crust of salt forms on leaves which tastes bad and the white
surfaces act to reflect light
Salt Glands
VASCULAR TISSUE
• Complex tissues: involve more than one kind of cell type.
• Vascular tissue is complex mix of parenchyma, sclerenchyma,
fiber cells, all non-transporting cells and those cells involved
in transport: vessels, tracheids or phloem tube, and ray cells.
XYLEM
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Xylem functions to:
 Transport water and dissolved substances
 Support the physical structure
 Can act in food storage
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Specific cells- Vessels:
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predominate in angiosperms;
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have short, wide, thick secondary cell walls;
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are dead, hollow cells; lack end walls;
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have a large diameter, therefore water movement through them is rapid;
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the wall thickenings in vessels are pitted as you can see from the image
on the right
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note the annular thickenings in cells below on left and the helical
thickenings in cells below on right which act to help support the walls
TRACHEIDS
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Predominate in conifers
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long, slender cells with tapered, overlapping ends;
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water moves upward from tracheid to tracheid through pit pairs,
thus preventing large gas bubbles from forming and thus no
cavitation during freezing/defrosting periods.
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Water can move through the plant with little seasonal disruption
allowing water flow and photosynthesis to occur year round.
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No need for loss of leaves in the winter as in most angiosperms
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Ray cells: regulate lateral transfer or storage.
PHLOEM
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Transports dissolved organic materials
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Living protoplasts at maturity; no nuclei; most organelles gone;
vacuole disappears; little protoplasm;
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An accessory companion cell= controls metabolic regulation as it
contains functional DNA. Note the narrow cell to the left of the one
with the arrow.
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Contain P-protein along longitudinal walls
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Sieve elements are the conducting cells of phloem.
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There are two kind of sieve elements:
 Sieve Cells
 Sieve Tube Members
• Sieve cells- occur in nonflowering plants; long with tapered
overlapping ends; associated with albuminous cells, which
help regulate the sieve cells' activities
• Sieve tube members- arranged end to end in sieve tubes;
larger pores than sieve cells; concentrated along contacting
end walls of adjacent sieve tube members
SPECIALIZED CELLS
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Root hairs- absorb water and the material it carries
(minerals); they increase absorptive surface area of roots.
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Although single celled, they can be viewed by the eye on rapidly
growing radishes.