The Shoot: Primary The Shoot: Primary Structure & DevelopmentStructure & Development

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ShootShoot

Above-ground partsAbove-ground parts Stem + leavesStem + leaves EmbryonicEmbryonic

Plumule – epicotyl, Plumule – epicotyl, 1 leaves, and SAM 1 leaves, and SAM SAM onlySAM only

SupportSupport ConductionConduction

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Shoot Shoot ComplexityComplexity

More complex than More complex than rootroot

Shoot has nodes (with Shoot has nodes (with leaves) and internodesleaves) and internodes

Root apex has no Root apex has no lateral organslateral organs

Gaps in vascular Gaps in vascular cylindercylinder

No root capNo root cap3

Origin & Growth of Primary Origin & Growth of Primary TissuesTissues

SAM -- repetitively SAM -- repetitively produces leaf produces leaf primordia and bud primordia and bud primordia – primordia – phytomeresphytomeres Leaf primordia – Leaf primordia –

leavesleaves Bud primordia – Bud primordia –

lateral shootslateral shoots

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Shoot ApexShoot Apex Shoot apex is Shoot apex is notnot synonymous with synonymous with

SAMSAM Shoot apex – SAM and subapical Shoot apex – SAM and subapical

region with leaf primordiaregion with leaf primordia

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Vegetative SAMVegetative SAM Tunica-corpusTunica-corpus

Tunica Tunica o One or more peripheral layersOne or more peripheral layerso Surface growth – anticlinal divisionsSurface growth – anticlinal divisions

Corpus Corpus o Interior layerInterior layero Volume growth – both anticlinal and Volume growth – both anticlinal and

periclinalpericlinal

Separate initialsSeparate initials

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Tunica-CorpusTunica-Corpus L1 – generally anticlinalL1 – generally anticlinal

If periclinal – cell becomes part of L2 If periclinal – cell becomes part of L2 and behaves accordingly – cell and behaves accordingly – cell differentiation differentiation positionalpositional..

Same for L2 and L3 layersSame for L2 and L3 layers

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Tunica-CorpusTunica-Corpus Central zone (promeristem) – corpus + Central zone (promeristem) – corpus +

adjacent tunica cellsadjacent tunica cells Peripheral zone/meristem – ring around Peripheral zone/meristem – ring around

central zonecentral zone Partly from tunica (L1 & L2) and partly from Partly from tunica (L1 & L2) and partly from

corpus (L3)corpus (L3) Pith MeristemPith Meristem

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Shoot Apical MeristemShoot Apical Meristem Central Zone -- Metaphysically Central Zone -- Metaphysically

equivalent to quiescent centerequivalent to quiescent center Peripheral zone – mitotically activePeripheral zone – mitotically active

Protoderm – L1Protoderm – L1 Procambium and part of ground Procambium and part of ground

meristem (cortex & maybe pith) – meristem (cortex & maybe pith) – peripheral meristemperipheral meristem

Rest of ground meristem (pith) – pith Rest of ground meristem (pith) – pith meristemmeristem

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Root vs Stem Root vs Stem DevelopmentDevelopment No regions in stem like in rootNo regions in stem like in root

SAM produces phytomeres so rapidly -- tissues SAM produces phytomeres so rapidly -- tissues initially indistinguishable initially indistinguishable On cell elongation, nodes/internodes recognizableOn cell elongation, nodes/internodes recognizable

Intercalary meristem – meristem between 2 or Intercalary meristem – meristem between 2 or more differentiated regionsmore differentiated regions Activity localizedActivity localized

SAM gives rise to same meristems as in rootSAM gives rise to same meristems as in root Protoderm, procambium and ground meristemProtoderm, procambium and ground meristem

Thickening – periclinal divisions and cell Thickening – periclinal divisions and cell enlargementenlargement

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Primary StructurePrimary Structure VariationVariation

Cortex around a central pithCortex around a central pitho Continuous cylinder of vascular tissueContinuous cylinder of vascular tissue

o Tilia americanaTilia americanao Cylinder of discrete strands/bundlesCylinder of discrete strands/bundles

o Sambucus canadensis , Ranunculus, Sambucus canadensis , Ranunculus, and and Medicago sativaMedicago sativa

Pith and cortex not separablePith and cortex not separableo Scattered vascular bundlesScattered vascular bundles

o Zea maysZea mays

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Primary StructurePrimary Structure

Primary StructurePrimary Structure

Primary StructurePrimary Structure

Vascular CylinderVascular Cylinder Vascular bundles separated by ground Vascular bundles separated by ground

meristemmeristem Interfascicular regions – connect cortex and Interfascicular regions – connect cortex and

pithpith Cortex – parenchyma and collenchymaCortex – parenchyma and collenchyma

1º phloem – outer cells of procambium1º phloem – outer cells of procambium 1º xylem – inner cells of the procambium1º xylem – inner cells of the procambium Vascular cambium – single layer of cells Vascular cambium – single layer of cells

betweenbetween meristematicmeristematic

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Vascular Vascular TissuesTissues

Fibers develop Fibers develop after internode after internode elongationelongation

First formed First formed 1º xylem and 1º xylem and 1º phloem 1º phloem stretched & stretched & destroyed destroyed during during elongationelongation

Vascular Vascular TissuesTissues

First formed 1º First formed 1º xylem and 1º xylem and 1º phloem stretched & phloem stretched & destroyed during destroyed during elongationelongation Protoxylem lacunaProtoxylem lacuna

Vascular Tissues of Stem Vascular Tissues of Stem & Leaf& Leaf

Inexorably tied Inexorably tied together – from together – from the beginning, the beginning, continuous with continuous with stemstem

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Vascular Tissues of Stem Vascular Tissues of Stem & Leaf& Leaf

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← ← TriticumTriticum meristem meristem

Vascular Vascular TissuesTissues

Leaf trace extends Leaf trace extends from stem bundle to from stem bundle to the leafthe leaf

Leaves can have Leaves can have multiple leaf tracesmultiple leaf traces

Sympodium – stem Sympodium – stem bundle and all bundle and all associated leaf associated leaf tracestraces

Branch trace – to Branch trace – to budsbuds

Leaf Traces & Leaf GapsLeaf Traces & Leaf Gaps Some sympodia interconnected; Some sympodia interconnected;

some independentsome independent Generally 2 branch traces/budGenerally 2 branch traces/bud

PhyllotaxyPhyllotaxy Opposite, alternate or whorledOpposite, alternate or whorled

Opposite: MADCap HorseOpposite: MADCap Horse …….. Remember Fibonacci?.. Remember Fibonacci?

First available spaceFirst available spaceo As soon as there’s enough space …..As soon as there’s enough space …..

Physiological field hypothesisPhysiological field hypothesiso Each new bud surrounded by a “zone of Each new bud surrounded by a “zone of

inhibition”inhibition” Biophysical forcesBiophysical forces

o Pressure causes buckling in tunicaPressure causes buckling in tunicao Expansin genes expressed at sites of Expansin genes expressed at sites of

primordium initiationprimordium initiation

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Morphogenesis Morphogenesis

Primary event – expansion of tissuePrimary event – expansion of tissue Subdivided by cell divisionSubdivided by cell division

Think tunica-corpus ……Think tunica-corpus ……

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Leaf Morphology Blade (lamina) Petiole Stipules sheath

Leaf MorphologyLeaf Morphology Simple vs CompoundSimple vs Compound

Simple may be Simple may be lobedlobed

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Simple vs Compound

Leaves -- lateral buds Leaflets -- same plane

Habitat FormsHabitat Forms MesophytesMesophytes

Size varies; thin cuticle; numerous Size varies; thin cuticle; numerous stomatesstomates

Palisade/spongy; bundle sheath cellsPalisade/spongy; bundle sheath cells

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Habitat FormsHabitat Forms HydrophytesHydrophytes

Large thin leaves; aerenchymaLarge thin leaves; aerenchyma Thin cuticle; stomates on Thin cuticle; stomates on upperupper surface surface Epidermis photosyntheticEpidermis photosynthetic

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Habitat FormsHabitat Forms XerophytesXerophytes

Small thick leavesSmall thick leaves Often sunken stomatesOften sunken stomates Thick cuticleThick cuticle

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MesophyllMesophyll Specialized for photosynthesisSpecialized for photosynthesis

Generally – spongy parenchyma & Generally – spongy parenchyma & pallisade parenchymapallisade parenchyma

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Vascular TissueVascular Tissue Permeates laminaPermeates lamina Branching patterns Branching patterns oftenoften characteristic characteristic

Monocot vs dicotMonocot vs dicot Xylem on topXylem on top

Why?????Why????? Minor veins vs Major veinsMinor veins vs Major veins Vascular bundles & bundle sheath cellsVascular bundles & bundle sheath cells

ProtectionProtection Filtering Filtering Bundle sheath extensions – conduits to Bundle sheath extensions – conduits to

epidermis?epidermis?

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Grasses and C4 Grasses and C4 photosynthesisphotosynthesis Different AnatomyDifferent Anatomy

No pallisade mesophyll – Krantz No pallisade mesophyll – Krantz anatomyanatomy

Mesophyll rings around bundle sheath Mesophyll rings around bundle sheath cellscellso Mestome sheath in C3 – thick wallsMestome sheath in C3 – thick walls

Distance between veinsDistance between veins

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Bulliform CellsBulliform Cells

In grasses – appear to function in In grasses – appear to function in folding/rolling of leaves – changes in folding/rolling of leaves – changes in turgor pressureturgor pressure

Leaf DevelopmentLeaf Development Chimera – different genotypesChimera – different genotypes

Only apical meristem – Only apical meristem – ColeusColeus and and CrotonCroton

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Leaf DevelopmentLeaf Development Founder cellsFounder cells

10-15 cells/layer in 10-15 cells/layer in ArabidopsisArabidopsis L1, L2, and L3L1, L2, and L3

First change is a Leaf ButtressFirst change is a Leaf Buttress Buttress → Leaf primordiumButtress → Leaf primordium

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Leaf DevelopmentLeaf Development

Tissue derives from only two tunica Tissue derives from only two tunica layers layers L1 – epidermisL1 – epidermis L2 & L3 – internal tissuesL2 & L3 – internal tissues

Intercalary growth Intercalary growth Cell divisionCell division Cell enlargementCell enlargement

Determinate – stops at the tip firstDeterminate – stops at the tip first

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Vascular DevelopmentVascular Development Differentiation of midvein from Differentiation of midvein from

procambiumprocambium Major veins develop “upward” with Major veins develop “upward” with

the procambiumthe procambium Minor veins – from margin in toward Minor veins – from margin in toward

midveins!midveins!

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Sun and Shade LeavesSun and Shade Leaves Sun Leaves – Smaller & ThickerSun Leaves – Smaller & Thicker

Palisade parenchymaPalisade parenchyma Vascular system more extensiveVascular system more extensive Internal surface area to leaf blade much Internal surface area to leaf blade much

higherhigher

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Leaf AbcissionLeaf Abcission Fall Color!Fall Color! Two layersTwo layers

Separation layer – poorly Separation layer – poorly developed cell wall developed cell wall thickeningsthickenings

Protective layer – isolates Protective layer – isolates leaf from plant – leaf scarleaf from plant – leaf scar

Enzymes break down Enzymes break down cell wallscell walls Weakening middle Weakening middle

lamellalamella Hydrolysis of cell wallsHydrolysis of cell walls

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Root/Shoot TransitionRoot/Shoot Transition Distribution and arrangement of Distribution and arrangement of

stele stele veryvery different! different! Solid cylinder → discrete vascular Solid cylinder → discrete vascular

bundlesbundles Transition initiated during Transition initiated during

embryogenesisembryogenesis One example …..One example …..

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Floral DevelopmentFloral Development Ends meristematic activity of shoot Ends meristematic activity of shoot

apexapex Transformation from vegetative to Transformation from vegetative to

reproductivereproductive Lots of environmental factorsLots of environmental factors

Day length, temperature, etc.Day length, temperature, etc. Increase in mitotic activityIncrease in mitotic activity Major changes in organizationMajor changes in organization

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Floral DevelopmentFloral Developmenta=floral apex; b=bract; s=sepals; p=petals; a=floral apex; b=bract; s=sepals; p=petals;

st=stamens; c=carpelst=stamens; c=carpel

Genetics of Floral Genetics of Floral DevelopmentDevelopment 3 genes – A, B, C3 genes – A, B, C

Stem & Leaf Stem & Leaf ModificationsModifications

TendrilsTendrils Modified stems – grapeModified stems – grape Modified leaves – peasModified leaves – peas

CladophyllsCladophylls Stems that look like leavesStems that look like leaves

Spines, thorns & pricklesSpines, thorns & prickles Spines – modified leavesSpines – modified leaves Thorns – modified stemsThorns – modified stems Prickles – epidermal outgrowthsPrickles – epidermal outgrowths

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Stem & Leaf Stem & Leaf ModificationsModifications

Food StorageFood Storage Tubers – aka Taters, precious!Tubers – aka Taters, precious! OnionsOnions GladiolusGladiolus KohlrabiKohlrabi

Water storageWater storage CactusCactus Agave/ AloeAgave/ Aloe

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