Roots

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Roots
Fibrous Roots
Tap Root
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Primary Root Growth
1 emerging lateral root, 2 lateral root
primordium,   3 root hair nearly fully grown, 4
mature vessel element, 5 level at which root
hairs appear, 6 endodermal cells differentiate,
7 level at which elongation ceases, 8 first
vessel element begins to differentiate, 9
region of maximum cell elongation, 10 first
sieve tube matures, 11 cell division ceases in
most cell layers, 12 first sieve element begins
to differentiate, 13 pattern of future vascular
cylinder becomes recognizable at this level, 14
zone of maximum rate of cell division, 15
apical initials, 16 root hair zone, 17 growth
in length, 18 elongation zone, 19 meristem,
20 rootcap
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Root hairs
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Dicot root with an actinostele
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Development of actinostele
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Monocot roots have a polyarch actinostele
Wheat Root
Lily Root
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Corn root with parenchyma in center of the stele
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Endodermis

• Stage I Endodermal cells have a Casparian Strip
• Stage II Endodermal cells develop suberin in
  all wall areas except for plasmodesmata
  especially inner tangential wall and radial walls
• Stage III Endodermal cell wall becomes
  thickened with added layers of cellulose and
  lignin
• Passage cells Endodermal cells that remain in
  Stage I condition while neighboring cells are in
  Stage II or III (often near xylem poles)
• Exodermis with similar properties occurs in some
  species just beneath the epidermis

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Endodermal cell with Casparian strip
Casparian strip
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Endodermis
Early stage of root development Later
stage of development
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Orchid roots are modified by development of a
velamen a multiple epidermis consisting of dead
cells an exodermis separates the velamen from
the cortex
Velamen
Exodermis
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Dicot root drawing at end of primary growth
1 epidermis 2 root hair, 3 cortex, 4
intercellular spaces, 5 pericycle (one layer
colored dark green), 6 endodermis, 7 primary
phloem, 8 protoxylem, 9 metaxylem, 10
initial vascular cambium, 11 sieve plate
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Branch roots
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Development of branch roots from pericycle
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Development of branch roots
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Branch root
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Branch root in corn
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Secondary Growth in Roots
1 primary xylem, 2 endodermis, 3 primary
phloem, 4 pericycle, 5 vascular cambium, 6
secondary phloem, 7 secondary xylem
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Limited secondary growth in castor bean root
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Tilia root
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Tilia root periderm
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Carrot roots have more secondary phloem than
xylem

• 1 secondary phloem,
• 2 vascular cambium,
• 3 parenchymatous woody secondary xylem

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Types of Mycorrhizae

• Ectotrophic mycorrhizae
• Sheathing mycorrhizae
• Endotrophic mycorrhizae
• VA (vesicular-arbuscule) mycorrhizae

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Ectotrophic Mycorrhizae

• Sheathing mycorrhizae of forest trees
• Roots have club-like appearance
• 5000 species of mushrooms form these

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Ectotrophic Mycorrhizae
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Ectotrophic Mycorrhizae
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Hartig Net
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Endotrophic Mycorrhizae

• Common on herbaceous plants and trees
• Mycelium branches in cortex of root forming
  arbuscles and vesicles

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Endotrophic Mycorrhizae
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VA Mycorrhizae
Arbuscule
Spore
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Roots and Shoots What connects the two areas?
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Hypocotyl connects the root and shoot starting in
the embryo
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