DICOT LEAF CUTICLE PALISADE PARENCHYMA (MESOPHYLL) UPPER EPIDERMIS BUNDLE SHEATH XYLEM PHLOEM.
Root Structure and Function Penetration of Soil Gravitropism Downward Growth Water and Mineral...
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Transcript of Root Structure and Function Penetration of Soil Gravitropism Downward Growth Water and Mineral...
Root Structure and Function
Penetration of Soil
Gravitropism Downward Growth
Water and Mineral Intake
Conduction (Xylem and Phloem)
Storage of Materials
Branching
Anchorage
Notice how the growing zone has no root hairs or lateral roots!
Growth among soil particles would result in shear forces.
Zone of Maturation - cell differentiationProtodermGround MeristemProvascular
Zone of Cell Elongation - cell expansion
Zone of Cell Division - new cells by mitosis
Root Cap - penetration, padding
Mucilage Slough Cells
Root Tip Senses GravityAuxin Hormone ProducedAuxin Accumulates on LowerGrowth Inhibited on Lower…Relative to UpperRoot Curves Downward
Gravitropism
Root Hairs Increase Surface Area
Root Hairs Secrete Acid (H+)
H+ Cation Exchange w/Minerals
Mineral Uptake into Roots
Water and Mineral Uptake
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96 N
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Radish seedlings have roots with long root hairs that increase the surface area for water and mineral uptake
Osmosis: passive movement of water from pure to polluted area
cytoplasmic solutesmore concentrated
soil solutes more dilute
cell membrane
Water potential low Water potential high
cell wall
water flow
Root hairs are responsible for cation exchange
soil particles covered with capillary waterand minerals
water
voids with air space
root hair penetrates soil spacesepidermal cell
cortex cell
H+
Ca2+H+Ca2+
Ca2+
intercellular gas space
to vascular cylinder
Dicot Mature Root Structure - Anatomy
Epidermis
Cortex
Vascular Cylinder
Ranunculus acris - buttercup
What does all of this autumn color (leaf senescence) have to do with roots?
Root Vascular Cylinder and Cortex Ranunculus acris - buttercup
Cortex
Endodermis
Meta-xylem
Phloem
PericycleProto-xylem
Endarch: protoxylem is inside the metaxylem
Exarch: protoxylem is outside the metaxylem √
haplostele
siphonostele
eustele
solenostele dictyostele
atactostele
leaf gap
leaf trace
cortexcortex phloem
xylem
cortexcortex phloem
xylem pithpith
dicot stem
monocot stem
Protosteles:actinostele plectostele
Specialized Versions
dicot root
monocot root
©19
96 N
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. W. N
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Com
panyApoplastic
Symplastic
xylem inside cortex outside
endodermis
suberin-waxy barrierto apoplastic
movement
cell membrane proteins (active transporters) determine which minerals may be taken up
The endodermis is thus responsible for selective mineral uptake.
minerals cannot go between cells
minerals must go through cells
Mineral uptake: Active transport against concentration gradient
cytoplasmic solutesmore concentrated
soil solutes more dilute
cell membrane
Water potential low Water potential high
cell wall
water flow
Ca2+
ATP
ADP + Pi
Ca2+Ca2+
Calcium transport protein
Osmosis: passive movement of water from pure to polluted area
too expensive?
Root Anatomy: Dicot Root Cross Section
Epidermis - root hairs, mineral and water intake
Cortex - storage, defense
Endodermis - selective mineral uptake
Pericycle - lateral root formation (periderm)
(Vascular Cambium - makes 2° tissues)
Phloem - CH2O delivery from leaves
Xylem - conduct water and mineral upwards
Casparian strips in radial walls
One Vascular Cylinder (Phloem + (Cambium) + Xylem)Radial Xylem-Phloem ArrangementExarch Xylem MaturationTetrarch (this example)
Monocot RootCross Section
Smilax-catbrier
Pith
Xylem/Phloem Arr?
Xylem Maturation?
______arch?
How is this section different?Smilax - catbrier
A closer look…What do these features tell you?
StarchCutin/Suberin
Mitochondria
Sieve Tube ElementCompanion Cell
Vessel with Lignin
Xylem Parenchyma
Lignified Pith Parenchyma
What is the Pericycle doing?
Root Cap
Zone of Cell Division
Growing out through cortex
In fibrous root systems, there is much lateral root formation.
Here you can see two root apices initiating from the
pericycle.
Notice their connection to the ridges of xylem
In shrubs like this tea plant (Camellia sinensis), the root system will be more tap root than fibrous root.
Notice the diameter of this tap root compared to this man’s waist!
But shrubs also generally have some compromise for uprooting forces…feeder roots extending laterally.
Tropical soils are nutrient poor.
Roots must traverse the surface for minerals, so roots grow on the surface (no tap root).
So, to keep this tall baobab tree standing upright, the roots grow in diameter but only in the vertical dimensions to form ridge roots…called buttress roots.
My wife here is as large as I am so you can see these roots are a meter tall!
These roots inspired gothic cathedral architects to design buttress walls.
http://www.dublincity.ie/dublin/citywalls/buttress.jpg
http://www.oxc.com.hk/raoul_nathalie/gallery/images/04%20Buttress.jpg
Pandanus utilis - screw pineProp roots such as these inspired flying buttresses.
http://www.contrib.andrew.cmu.edu/~ajm/Pages/Graphics/flyingbuttress.JPG
http://williamcalvin.com/BHM/img/FlyingButtressND.jpg
Avicennia germinans (black mangrove)
pneumatophores