Chapter 25 The Shoot: Primary Structure and Development

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Chapter 25The Shoot Primary Structure and
Development
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Outline

• Intro
• Origin and growth of 1 tissues of the stem
• 1 structure of the stem
• Relation btwn vascular tissues of stem and leaf
  morphology and leaf structure
• Grass leaves
• Development of the leaf
• Leaf abscission
• Transition btwn vascular systems of root and
  shoot
• Development of the flower
• Stem and leaf modifications

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Intro

• 1 tissues arise from shoot apical meristem
• Shoot stem leaves
• aboveground portion of plant
• 1 func. of stems
• support, conduction
• 1 func. of lvs
• Ps
• Terms
• node
• internode
• bud
• leaf

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Primary Tissues

• Shoot apical meristem
• produces new cells, leaf and bud primordia
• pattern of repeated units (phytomeres)
• leaf primordia develop into lvs
• bud primordia develop
  into lateral shoots
• Stem length due to
  cell elongation

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Tissue Organization

• Vegetative shoot apex has tunica-corpus
  organization
• difference btwn tunica and corpus is plane of
  cell division
• tunica outermost layer of cells, divide
  anticlinally
• anticlinal division perpendicular to meristem
  surface
• ? cells on surface
• corpus cells beneath tunica, divide anti- and
  periclinally
• periclinal division parallel to meristem
  surface
• add bulk to shoot
• L1 - outer
• L2
• L3 - inner

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Tissue Organization

• Central mother cell zone area of few divisions
• similar to quiescent center
• part of corpus
• Peripheral zone peripheral meristem
• ring around mother zone
• Pith meristem beneath central mother zone

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Tissue Origins

• Apical meristem gives rise to
• protoderm originates from tunica (L1)
• procambium originates from peripheral meristem
  (tunica and corpus)
• ground meristem originates from peripheral and
  pith meristems
• Apical meristem produces leaf primordia, nodes,
  and internodes
• packed in buds
• growth occurs via intercalary meristem
• area btwn nodes
• internodal elongation
• protoX and protoP form
• stem thickening during 1 growth due to
  periclinal divisions cell enlargement

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Vascular System Organization

• 3 types of organization of vascular system
• continuous cylinder in ground tissue (eudicots)
  (Tilia)
• cylinder of discrete bundles separated by ground
  tissue (eudicots) (Sambucus, Medicago,
  Ranunculus)
• bundles scattered or in ring of ground tissue
  (monocots herbaceous eudicots) (cortex and pith
  not distinct) (Zea)

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1 Structure of Stems

• Tilia (basswood)
• almost continuous cylinder of 1 vascular tissue
• bundles separated by thin regions of parenchyma
  (interfascicular parenchyma)
• connect cortex and pith
• (inter btwn, intra across, fascicle
  bundle)
• epidermis 1 cell thick, few stomata
• procambium produces 1 P outside, 2 X inside, VC
  btwn
• 1 P fibers form in 1 P

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1 Structure of Stems

• Sambucus (elderberry)
• wide interfascicular area (pith rays)
• thus discrete bundles
• procambial strands differentiate into X and P
• protoX and protoP
  
  first-formed
  X and
  P
• X and P stretched
  during stem
  
  elongation
• destroyed
• Interfascicular
  fascicular
  cambiums

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1 Structure of Stems

• Medicago (alfalfa)
• herbaceous (non-woody)
• VC derived from procambium (fascicular) and
  interfascicular parenchyma
• Ranunculus (buttercup)
• vascular bundles similar to monocots
• after 1 X and P mature, procambium disappears
• thus no VC
• thus no potential for later growth (closed)
• vs. open bundles produce VC

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1 Structure of Stems

• Zea (corn, monocot)
• vascular bundles scattered
• closed

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1 Structure of Stems

• stages of vascular bundle differentiation
• schlerenchyma sheath covering when mature

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Vascular Tissue Connections

• Procambium arises behind apical meristem
• mature upward as stem grows
• outward as leaf develops
• continuum btwn leaf and stem
• At each node
• vascular bundles diverge from vascular cylinder
  into leaf
• leaf trace extensions of vascular
  system in stem that
  go to leaf
• leaf trace gap gap in vascular
  cylinder above leaf
  trace
• branch trace extensions of
  vascular system
  in stem that
  go to branch
• branch trace gap gap in
  vascular cylinder
  above branch trace

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Pattern of Leaf Arrangement

• Phyllotaxy arrangement of lvs on stem
• alternate 1 leaf per node
• spiral most common
• two opposite ranks distichous
• opposite 2 leaf per node
• pairs are right angles to previous and following
  pairs decussate
• whorled 3 lvs per node
• Hypotheses
• field hypothesis of phyllotaxy
• physiological field surrounding leaf primordia
  inhibits initiation of new primordia
• first available space hypothesis
• primordia arise in first available space
• biophysical force hypothesis
• primordia arise when tunica surface
  bulges/buckles due to pressure