Plant Structure

1
Plant Structure

• Chapter 35

2
3 Basic Plant Organs

• roots
• stems
• leaves

3
Roots

• functions
• anchors plant
• absorbs minerals water
• occurs near root tips where tiny root hairs
  increase surface area for absorption
• stores organic nutrients
• 2 types of root systems
• taproot one main root with many lateral roots
• fibrous many small roots grow from the stem
  (adventitious)

4
Stems

• consist of an alternating system of nodes (points
  at which leaves attached) internodes (stem
  segments between nodes)
• in angle formed by leaf stem is an axillary bud
  which can become a branch
• at stem apex is a terminal bud which has apical
  dominance and, thereby, inhibits growth of
  axillary buds
• types of modified stems stolons, rhizomes,
  tubers, bulbs

5
Leaves

• main photosynthetic organ
• consists of blade petiole (stalk)
• veins can be parallel (monocots) or netlike
  (eudicot)
• simple versus compound leaves

6
3 Tissue Systems

• dermal
• vascular
• ground

7
Dermal Tissue

• outer protective covering
• consists of a single layer of cells (epidermis)
  in nonwoody plants
• consists of protective tissue layers (periderm)
  in older regions of woody plants
• epidermis has a waxy cuticle to help prevent
  water loss

8
Vascular Tissue

• carries out long-distance transport between roots
  and shoots
• 2 types
• xylem conveys water dissolved minerals from
  roots to shoots
• phloem transports organic nutrients from source
  to sink
• xylem phloem are collectively called the stele
• in roots, the stele is a solid central cylinder
• in stems leaves, the stele is divided into
  vascular bundles

9
Ground Tissue

• tissues that are neither dermal nor vascular
• if located internal to vascular tissue it is
  called pith
• if located external to vascular tissue it is
  called cortex

10
Stem Tissue Organization

• epidermis covers stem
• vascular tissue runs length in bundles
• lateral shoots arise from axillary buds
• vascular bundles converge with root vascular
  cylinder at zone of transition

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Leaf Tissue Organization

• epidermis has pores called stomata flanked by two
  guard cells
• ground tissue (mesophyll) between upper lower
  epidermis
• palisade upper layer of elongated cells
• spongy lower layer of loosely arranged cells
• vascular tissue (veins) enclosed by protective
  bundle sheath cells

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Types of Plant Cells

• parenchyma perform metabolic functions
• collenchyma provide flexible support without
  restraining growth of young parts of plant shoot
• sclerenchyma provide rigid support have thick
  secondary walls strengthened by lignin
• tracheids vessel elements found in xylem
• sieve-tube members make up phloem
• companion cells serve sieve-tube members

13
Plant Growth

• Chapter 35

14
Indeterminate Growth

• plant growth is not limited to an embryonic or
  juvenile stage
• this is due to meristems (perpetually embryonic
  tissues)
• apical meristems
• located at tips of roots and in buds of shoots
• associated with primary growth (length)
• lateral meristems
• cylinders of cells located along length of roots
  stems
• includes vascular cambium cork cambium
• associated with secondary growth (girth)

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Types of Growth

• primary growth
• produces primary plant body parts of the root
  and shoot systems produced by apical meristems
• secondary growth
• produces secondary plant body growth in
  thickness produced by lateral meristems (vascular
  cambium cork cambium)
• commences where primary growth has stopped
• occurs in stems roots process is similar

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Primary Growth Roots

• growth occurs just behind the root tip
• 3 zones
• division
• elongation
• maturation
• produces epidermis, ground tissue, vascular
  tissue

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Primary Growth Shoots

• leaves arise as leaf primordia along flanks of
  apical meristem
• axillary buds form in meristematic cells at based
  of leaf primordia

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Secondary Growth

• vascular cambium
• cylinder of meristematic cells one cell thick
• increases circumference thickens
• lays down secondary xylem phloem
• cork cambium
• replaces epidermis produces periderm

19
Plant Development

• Chapter 35

20
Plant Morphogenesis

• influenced by
• plane symmetry of cell division
• direction of cell expansion
• positional information
• homeotic genes

21
Cell Division

• asymmetrical cell division unequal division of
  the cytoplasm
• (ex) formation of guard cells
• preprophase band ring of microtubules that
  predicts the plane of cell division

22
Cell Expansion

• due to water uptake into vacuole pressure on a
  cell wall that has been weakened by enzymes
• direction depends on orientation of cellulose
  microfibrils in the cell wall

23
Pattern Formation

• development of specific structures in specific
  locations is due to
• positional information in the form of signals
  from neighboring cells
• regulatory genes called homeotic genes
• (ex) genetic control of flowering

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Genetic Control of Flowering

• involves a developmental phase change
• juvenile ? adult vegetative ? adult reproductive
• transition from vegetative growth to flowering is
  associated with the switching on of floral
  meristem identity genes which produce
  transcription factors that convert indeterminate
  vegetative meristems to determinate floral
  meristems
• floral pattern is controlled by organ identity
  genes ABC model (see next slide)

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