Cells & TissuesCells & Tissues

Apical MeristemsApical Meristems Tips of roots and shootsTips of roots and shoots Extension of plant bodyExtension of plant body InitialsInitials

One cell remains as initial – maintaining One cell remains as initial – maintaining meristemmeristem

Other cell is derivative – new body cellOther cell is derivative – new body cell

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Primary MeristemsPrimary Meristems

Multiple divisions before differentiationMultiple divisions before differentiation Partly differentiated tissuePartly differentiated tissue

Primary growthPrimary growth Extension of the plant bodyExtension of the plant body

Secondary growthSecondary growth Thickening of the plant bodyThickening of the plant body

Indeterminate growthIndeterminate growth Formation of new organs during their Formation of new organs during their

entire lifeentire life

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Growth, Morphogenesis Growth, Morphogenesis & Differentiation& Differentiation

Development – sum total of events that Development – sum total of events that form an organisms bodyform an organisms body Driven by geneticsDriven by genetics In response to environment: day length, In response to environment: day length,

light quality/quantity, temperature, gravitylight quality/quantity, temperature, gravity Development – 3 processesDevelopment – 3 processes

GrowthGrowth MorphogenesisMorphogenesis Differentiation Differentiation

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GrowthGrowth

Combination of cell division and Combination of cell division and elongationelongation Cell division alone only increases Cell division alone only increases

number!number! Most growth – elongation & Most growth – elongation &

enlargementenlargement

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MorphogenesisMorphogenesis

Primary event – expansion of tissuePrimary event – expansion of tissue Subdivided by cell divisionSubdivided by cell division Cell/tissue differentiation follow Cell/tissue differentiation follow

morphogenesismorphogenesis

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DifferentiationDifferentiation

Often begins while cell is still enlargingOften begins while cell is still enlarging Depends on gene expressionDepends on gene expression Ultimate fate positionalUltimate fate positional

Not dependant on cell lineageNot dependant on cell lineage DeterminationDetermination

Commitment to specific course of Commitment to specific course of developmentdevelopment

Competency Competency Ability of cell to develop in response to Ability of cell to develop in response to

specific signalspecific signal7

DifferentiationDifferentiation

Internal OrganizationInternal Organization Cells Cells tissues tissues tissue systems tissue systems Tissue SystemsTissue Systems

GroundGround VascularVascular Dermal Dermal

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Tissue SystemsTissue Systems GroundGround

ParenchymaParenchyma CollenchymaCollenchyma Sclerenchyma Sclerenchyma

VascularVascular XylemXylem PhloemPhloem

DermalDermal Epidermis Epidermis periderm periderm

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Tissue SystemsTissue Systems Characteristic Distribution PatternsCharacteristic Distribution Patterns

Primary difference – vascular/ground Primary difference – vascular/ground tissuetissue

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Fig 12.1

ROOT

STEM

Dicot vs Monocot

TissuesTissues

Functionally/ structurally distinct Functionally/ structurally distinct cellscells

Simple tissues – one type of cellSimple tissues – one type of cell Ground tissuesGround tissues

Complex tissues – more than 1 type Complex tissues – more than 1 type of cellof cell Vascular tissuesVascular tissues Dermal tissuesDermal tissues

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Ground Tissues -- Ground Tissues -- ParenchymaParenchyma

Living at maturity Living at maturity Capable of cell divisionCapable of cell division Some have 2º cell wallsSome have 2º cell walls Adventitious rootsAdventitious roots Photosynthesis, storage & secretionPhotosynthesis, storage & secretion

““chlorenchyma”chlorenchyma” Movement of water and foodMovement of water and food

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Parenchyma – Transfer Parenchyma – Transfer CellsCells Increased surface areaIncreased surface area

Facilitates movement of solutes over short distancesFacilitates movement of solutes over short distances Intensive solute transferIntensive solute transfer

Common Common Associated with xylem/phloem of minor veins Associated with xylem/phloem of minor veins

CotyledonsCotyledons Leaves in herbaceous EudicotsLeaves in herbaceous Eudicots Leaf tracesLeaf traces

Reproductive tissues – placentae, endosperm …Reproductive tissues – placentae, endosperm … Glandular structures – nectaries, salt glands …Glandular structures – nectaries, salt glands …

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Ground Tissues -- Ground Tissues -- CollenchymaCollenchyma

Living at maturityLiving at maturity Discrete strands of elongated cells Discrete strands of elongated cells

Continuous cylinders in stems and Continuous cylinders in stems and petiolespetioles

Borders veins in Eudicot leavesBorders veins in Eudicot leaves Unevenly thickened, nonlignified cell Unevenly thickened, nonlignified cell

wallswalls Supports young growing organsSupports young growing organs

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Ground Tissues -- Ground Tissues -- SclerenchymaSclerenchyma

Continuous masses or small groupsContinuous masses or small groups Hard, lignified cell wallsHard, lignified cell walls Strengthening and supporting plant partsStrengthening and supporting plant parts FibersFibers

Long, slender cells Long, slender cells o strands or bundlesstrands or bundles

Bast fibersBast fibers Sclerids Sclerids

Variable in shapeVariable in shape Seed coats, nut shells, endocarpSeed coats, nut shells, endocarp

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Vascular Vascular TissueTissue

Xylem and Xylem and PhloemPhloem Conducts Conducts

water and water and nutrientsnutrients

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Vascular Tissues -- XylemVascular Tissues -- Xylem Conducts waterConducts water

Also conducts mineralsAlso conducts minerals SupportSupport Food storageFood storage

1º growth – procambium1º growth – procambium 2º growth – vascular cambium2º growth – vascular cambium Dead at maturity Dead at maturity

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Vascular Tissues -- XylemVascular Tissues -- Xylem Trachery elementsTrachery elements

Tracheids Tracheids Vessel elementsVessel elements

May have wall pitsMay have wall pits

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A-C – vessel elementsD – tracheidE-F -- fibers

Xylem – Vessel ElementsXylem – Vessel Elements

Vessel elements – perforation plateVessel elements – perforation plate End rimsEnd rims

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Xylem -- TracheidsXylem -- Tracheids

Less specializedLess specialized No perforationsNo perforations Seedless vascular plants & Seedless vascular plants &

Gymnosperms Gymnosperms Only water conducting cellsOnly water conducting cells

Less efficient because of lack of Less efficient because of lack of perforationsperforations

Safer because of pit membranesSafer because of pit membranes Stop air bubblesStop air bubbles

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Xylem -- TracheidsXylem -- Tracheids

Variety of 2º wall thickeningsVariety of 2º wall thickenings During elongation – spiral or annularDuring elongation – spiral or annular Allow for extension after differentiationAllow for extension after differentiation

Programmed cell deathProgrammed cell death Only cell walls retainedOnly cell walls retained

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Xylem – Miscellany Xylem – Miscellany

Parenchyma – stores stuffParenchyma – stores stuff Vertical strandsVertical strands In rays -- 2º xylem In rays -- 2º xylem

FibersFibers Storage and supportStorage and support May be livingMay be living

ScleridsSclerids

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Vascular Tissue -- Vascular Tissue -- PhloemPhloem

Principal food-conducting tissuePrincipal food-conducting tissue Not just sugars!Not just sugars! Long distance signaling moleculesLong distance signaling molecules

1º or 2º growth1º or 2º growth Sieve elements – principal conducting cellsSieve elements – principal conducting cells

Sieve areas connecting adjacent sieve Sieve areas connecting adjacent sieve elementselements

Sieve cells – only phloem tissue in Sieve cells – only phloem tissue in gymnospermsgymnosperms

Sieve-tube elements – only angiospermsSieve-tube elements – only angiosperms

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PhloemPhloem

Sieve CellsSieve Cells Narrow pores Narrow pores Uniform sieve areasUniform sieve areas

Sieve-tube elementsSieve-tube elements Sieve PlateSieve Plate

o Some areas Some areas larger pores larger pores

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PhloemPhloemSieve CellsSieve Cells

Narrow pores Narrow pores Uniform sieve areasUniform sieve areas

Sieve Tube ElementsSieve Tube Elements

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Sieve ElementsSieve Elements Living at maturityLiving at maturity DifferentiationDifferentiation

Trachery elements – complete breakdownTrachery elements – complete breakdown Sieve elements – partial breakdownSieve elements – partial breakdown

o Breakdown of nucleus, loss of ribosomes, Breakdown of nucleus, loss of ribosomes, Golgi & cytoskeletonGolgi & cytoskeleton

o Remainder distributed along wall → plasma Remainder distributed along wall → plasma membrane, SER, some plastids & membrane, SER, some plastids & mitochondriamitochondria

P-protein – except in some monocotsP-protein – except in some monocots

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Sieve Tube ElementsSieve Tube Elements

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Arrows show P-protein bodies

Sieve-tube ElementsSieve-tube Elements Companion Cells – Companion Cells –

specialized parenchymaspecialized parenchyma Same mother cellSame mother cell Deliver stuff to sieve-tube Deliver stuff to sieve-tube

elementselements Hormones, proteins, ATP, Hormones, proteins, ATP,

etc.etc. Life support system for Life support system for

STESTE Companion cell dies when Companion cell dies when

sieve element cell diessieve element cell dies

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Sieve-Tube Element Sieve-Tube Element DifferentiationDifferentiation

Gymnosperm Sieve CellsGymnosperm Sieve Cells

Associated with albuminous cellsAssociated with albuminous cells Have nucleus, etc.Have nucleus, etc. Similar function to companion cellsSimilar function to companion cells Also dies when sieve element cell diesAlso dies when sieve element cell dies

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Dermal TissueDermal Tissue

Epidermis – outermost layerEpidermis – outermost layer Variable functionally & structurallyVariable functionally & structurally

Unspecialized or specialized!Unspecialized or specialized! Guard cellsGuard cells Trichomes Trichomes

Protects plantProtects plant cuticlecuticle

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Epidermis – Guard CellsEpidermis – Guard Cells Contain chloroplastsContain chloroplasts Regulate stomatal openingRegulate stomatal opening

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Epidermis -- TrichomesEpidermis -- Trichomes Root hairsRoot hairs Increased reflection of radiation Increased reflection of radiation

lower tempslower temps Lower water lossLower water loss

Absorption of water and mineralsAbsorption of water and minerals Secretory functionsSecretory functions Protection against herbivory Protection against herbivory Carniverous plantsCarniverous plants

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TrichomesTrichomes

Carnivorous PlantsCarnivorous Plants

Nepenthes Drosera Dionaea

PeridermPeriderm 2º protective tissue2º protective tissue

Replaces epidermis in Replaces epidermis in 2º growth2º growth

Cork (phellem) → Cork (phellem) → nonlivingnonliving

Cork cambium Cork cambium (phellogen)(phellogen) Cork – outer surfaceCork – outer surface Phelloderm -- innerPhelloderm -- inner

Phelloderm – living Phelloderm – living parenchyma tissueparenchyma tissue

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Periderm -- LenticelsPeriderm -- Lenticels Loosely arrangedLoosely arranged Gas exchange across the corkGas exchange across the cork

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