Transcript
Plant Tissue
Plant tissues fit into 3 main categories:
Dermal tissues: epidermis, trichomes (“hairs”), guard cells, root hairs
Ground tissues: parenchyma (with chloroplasts = chlorenchyma), sclerenchyma, collenchyma
Vascular tissues: xylem (dead at maturity: tracheids and vessel elements), phloem (living: sieve tube cells [no nuclei], companion cells [with nuclei])
Meristematic tissues – localized regions of cell division
1. Apical Meristems◦ Primary or Transitional Meristem Primary growth
Protoderm gives rise to epidermis Ground meristem gives rise to ground tissue Procambium gives rise to 1
o vascular tissue
2. Lateral Meristems◦ Vascular cambium 2
o vascular tissue
◦ Cork cambium or phellogen periderm
3. Intercalary Meristems (found in the nodes of grasses)
lateral branch
root
shoot
axillarybud
shootapex
lateralbranch
node
internode
root tip
root apicalmeristem
root cap
root hairs
shoot tip
shoot apicalmeristem
budprimordium
lateral roots
meristem - region of actively dividing cells 1) apical (shoot & root);
2) lateral (vascular & cork cambia)
Cell differentiation:1) Cell expansion (elongation)2) Cell maturation / specialization
Derivation from the Apical Meristem
Plant Body Organization11
Meristems are clumps of small cells with dense cytoplasm and large nuclei
They act as stem cells do in animals-One cell divides producing a differentiating cell and another that remains meristematic
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Dermal Tissues
dermal tissues cover the organs of a plant. They are analogous to skin.
epidermisoutermost layer of cellsusually one cell layer thickepidermal cells have a layer of cutin (cuticle)
resistant to bacteria and other disease organisms
Plant Epidermis
1. Outer layer covering primary plant body
2. Interface through which plant interacts with external environment
3. Replaced by cork or bark in plants with secondary growth
Function of Epidermis
1. Protection1. Sunlight2. Other organisms3. Abiotic damage
2. Regulates water movement1. Uptake and loss2. Shoot reduces water loss3. Root regulates absorption
3. Secretion
Cell Wall and its Coverings
1. Epidermal Cell Wall – varies in thickness
2. Cuticle – made of cutin and waxes
3. Cutin – high molecular weight lipid polyester material C16Hn or C18Hn or a combination of both
1. Arrangement 1 – cutin + cell wall2. Arrangement 2 – cutin pectin cell wall
4. Wax layer 1. epicuticular (on surface) 2. intercuticular (pockets inside cuticle)
Epicuticular Waxes
Epidermal Cells – Ordinary Cells
Ordinary Cells1. Dicots – sinuous cell wall
2. Monocots – “straight” cell walls
3. No intercellular spaces
4. Typically no chloroplasts (exceptions??)
5. May have leucoplasts (plastids that do not have any pigments)
Epidermal Cells – Guard Cells and Stomata
Stomata1. Openings in epidermis2. Occur on all aerial parts of plant3. Most abundant on leaves; typically absent in
roots4. Pore size regulated by guard cells
Guard Cells1. Found on all green plants and flower parts2. Regulate gas exchange (CO2 and H2O vapor)3. Special arrangement of microfibrils in cell wall
allows pore to open and close between guard cells
Epidermal Cells – Trichomes
1. Highly variable appendages of the epidermis
2. Living or dead, uni- or multicellular
3. Lots of forms: glandular, nonglandular, scales, papillae, absorbing hairs of roots…
4. Functions – highly variable including protection, excretion, reflection, water absorption, water shedding…
Epidermal cells of root showing formation of root hairs from single cells.
Cuticle Wax
Wax MyrtleMyrica
ceriferawaxes
obtained from boiling the leaves is used to make bayberry candles
Epidermis is made of many types of cells
1. Guard cells form stomata2. Trichomes
Outgrowths – ‘hairs’ Some leaf trichomes use to
keep animals away Some used to eliminate salt Some thought to increase
reflection to reduce stem/leaf temperature
Root hairs are a type of trichome, increase surface area to increase uptake of nutrients
3. Glands
Root Hairs are extensions of
epidermal cells
Dermal Tissues: Epidermis
Glands secrete substances that protect the plant
secrete nectardigestive glandsSundewstrigger hairs of a
Venus Flytrap
Prickles grow out of the epidermis
A Few Definitions
Periderm = secondary tissue replaces epidermis in roots and stems consists of phellem, phellogen, and phelloderm
Phellem corky tissues non-living suberized cells produced by the cork cambium (phellogen) to outside of
stem
Phellogen cork cambium produces cork to the outside produces phelloderm to the inside
Phelloderm parenchyma-like cells produced toward inside of stem by the cork cambium
(phellogen)
Dermal tissue: Periderm
How is the periderm like the layer of dead skin cells on human skin?Replaces epidermis on roots and stems of woody plants with age.
The periderm composed mainly of thick, waterproof cork cells.
Protects stems and root
Ground TissuesGround tissue functions
metabolism: conduct photosynthesis; regulate gas exchangestorage: photosynthate (sugar, starch), water, & proteins support: via cellulose and lignin
Ground tissuesParenchyma
undifferentiated, thin, living cells; extremely common ‘filler;’ storage; photosynthesis; tissue healing
Ground tissuesCollenchyma
unevenly thickened, living cells; sub-epidermal FLEXIBLE support
Ground tissuesSclerenchyma
thick & lignified; non-living cells at maturityRIGID support; conduction
Ground tissue: Parenchyma
What can you see in these parenchyma cells?oThin-walled cellsoAlive at maturityoMany functions, including photosynthesis, starch storage, hormone production.
Ground Tissue: Collenchyma
How might support cells be different from other plant cells?
Plants don’t have a skeletal system as humans do. What holds a plant up?
What features do you see in these cells?
Flexible support tissue.Elongated cells with irregular shapes and
unevenly thickened walls.Living at maturity.
Ground tissue: Sclerenchyma
How are these thick-walled cells different from collenchyma cells?
What features do you see in these cells?Sclerenchyma cells are dead at maturity.
Why might that be?
Support tissue.Elongated cells with thick cell walls.Dead at maturity.Forms long fibers, or smaller
sclerids (such as stone cells in pears).
Ground Tissue
Parenchyma: Gen. metabol.1) Isodiametric to elongate
2) Primary cell wall 3) Living
Collenchyma: support
1) Elongate2) Primary cell wall thick, uneven, rich in pectins
3) Living
Ground Tissue
Sclerenchyma1) Secondary cell wall (+ primary)
2) Dead at maturity (usually)
Fibers
Elongate, sharply tapering
Ground Tissue
Sclerenchyma1) Secondary cell wall (+ primary)
2) Dead at maturity (usually)
Sclereids Isodiametric to irregular
VASCULAR TISSUE XYLEM and PHLOEM
1. Structurally and functionally complex tissue
2. Continuous through plant as veins
3. Typically associated with each other
4. Functions1. Water movement (Tracheids and Vessel members)2. Storage (parenchyma)3. Support (fibers and sclereids)
Vascular Tissue
XylemWater & mineral conductionTracheary elements + parenchyma + sclerenchyma
PhloemSugar conductionSieve members + parenchyma + sclerenchyma
- Both complex tissues
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Looking at the Vascular Bundle
Xylem and phloem found together in “collateral bundle”
In stem: Phloem toward epidermis Xylem toward center
In Leaf: Phloem toward bottom (abaxial) Xylem toward top (adaxial)
1 = apical meristem, 2 = procambium, 3 = protoderm, 4 = ground meristem, 5 = primary phloem, 6 = primary xylem, 7 = leaf trace, 8 = pith ray, 9 = pith, 10 = epidermis
Vascular tissue: Xylem
Xylem tissue moves water. What features would the cells need to carry out this function?
What features do you see in these cells?
Long, tube-like cells, joined end-to end, that transport water and minerals from soil to leaves.
Two types of cells: tracheids (in conifers) and vessel elements (in flowering plants).
Vascular tissue: Phloem
Phloem tissue moves sap, which is sugar dissolved in water. What features would the cells need to carry out this function?
What features do you see in these cells?
XYLEM in the Primary Plant Body
Found in Higher plants (tracheophytes)
Transport water and nutrients by bulk flow
Several types of cells and structures• Tracheary elements (conduct water)• Xylary Fibers (support)• Parenchyma (storage)• Perforation plate (perforated part of a cell wall usually
found at the end) Protoxylem (still elongating) and Metaxylem (elongation
complete)
Tracheary Elements: Tracheids
Found in both gymnosperms and angiospermsDead at maturitySo-so water movementSmall diameter with angular end wallsNO perforation plates in end wallsWater moves through pairs of pits (holes) in
adjacent cell walls
Tracheary Elements: Vessel Members
Found only in angiospermsDead at maturityGood water movementLarge diameter and nearly circular in cross
sectionVariety of perforation plate types in end wallsWater moves through pairs of pits (holes) in
adjacent cell walls
1 = annular thickening; 2 - 4 = helical thickenings; 5 = reticulate thickening; 6 = scalariform pitting; 7 = opposite pitting; 8 = alternate pitting
Pitting in Vessel Members
simple to more advanced
Phloem
Function is carbohydrate and nutrient transport Always from source to sink Living tissue with short functional life (days to
one season) Very fragile 1o cell wall Velocity of movement 10 – 100 cm/hr Component of phloem tissue
◦ Sieve elements (sieve cells and sieve tube elements◦ Parenchyma◦ Companion cells◦ Fibers◦ sclereids
1 = companion cells;
2 = sieve tube content;
3 = parenchyma cell;
4 = sieve plate (oblique view);
5 = one sieve element;
6 = sieve plate (side view);
Sieve tube and companion cells in the phloem of squash
SIEVE ELEMENTS
No functional nucleus
Few organelles, no vacuole when mature
Two types1. Sieve Cells (gymnosperms and lower vascular
plants only)
2. Sieve Tube Members (flowering plants)
SIEVE ELEMENTSSieve Cells
Lower vascular plants and gymnosperms
Long and gradually taperingEnd wall poorly definedModerate efficiency for moving sapSide walls covered with primary pit
fields
SIEVE ELEMENTSSieve Tube Members
Flowering plants onlyBroad cell end wall – covered by sieve
plateMore than one stacked on top of each
other = Sieve tubeTwo types of sieve plates
Simple
Compound
1 = inclined simple sieve plate; 2 = phloem parenchyma cells, 3 = companion cell; 4 = sieve tube members
“Helper” Cells
1. help load sieve elements with photosynthates in source area and unload in sink areas.
2. Ribosomes provide sieve elements with essential proteins and ATP.
3. Companion cells and sieve elements together constitute a functional unit in food conductance.
4. Two Types1. Albuminous cells in Gymnosperms with sieve
cells 2. Companion cells in Angiosperms with sieve
tube members
Albuminous Cells
Only in gymnosperms
Specialized type of parenchyma
Very small in comparison to sieve cell
The number associated with a sieve cell varies
Tracheary Elements
Tracheids - Imperforate Vessels - Perforate
Angiosperms (most)
Gnetales
A few Monilophytes
Sieve ElementsSieve cells - No sieve plates Sieve tube members -
Sieve plates
Apomorphy of Angiosperms
Vascular cambium - a lateral meristem
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