The Shoot: Primary Structure & Development 1. Shoot Above-ground parts Above-ground parts Stem +...
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Transcript of The Shoot: Primary Structure & Development 1. Shoot Above-ground parts Above-ground parts Stem +...
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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