1. Root Structure and Function
Penetration of Soil
Gravitropism Downward Growth
Water and Mineral Intake
Conduction (Xylem and Phloem)
Storage of Materials
Branching
Anchorage

2. Zone of Maturation - cell differentiation
Protoderm
Ground Meristem
Provascular
Zone of Cell Elongation - cell expansion
Notice how the growing zone has no root hairs or lateral roots!
Growth among soil particles would result in shear forces.
Zone of Cell Division - new cells by mitosis
Root Cap - penetration, padding

3. Slough Cells
Mucilage

4. Gravitropism Root Tip Senses Gravity Auxin Hormone Produced
Auxin Accumulates on Lower
Growth Inhibited on Lower…
Relative to Upper
Root Curves Downward
Water and Mineral Uptake
Root Hairs Increase Surface Area
Root Hairs Secrete Acid (H+)
H+ Cation Exchange w/Minerals
Mineral Uptake into Roots

5. Radish seedlings have roots with long root hairs that increase the surface area for water and mineral uptake
©1996 Norton Presentation Maker, W. W. Norton & Company

6. Osmosis: passive movement of water from pure to polluted area
cell membrane
cell wall
water flow
cytoplasmic solutes
more concentrated
soil solutes more dilute
Water potential low
Water potential high

7. Ca2+ Ca2+ Ca2+ Root hairs are responsible for cation exchange
cortex cell
root hair penetrates soil spaces
epidermal cell
soil particles covered with capillary water
and minerals
intercellular gas space
Ca2+
Ca2+ H+
Ca2+ H+
to vascular cylinder
voids with air space
water

8. Dicot Mature Root Structure - Anatomy
Ranunculus acris - buttercup
Epidermis
Cortex
Vascular Cylinder

9. What does all of this autumn color (leaf senescence) have to do with roots?

10. √ Root Vascular Cylinder and Cortex Endodermis Cortex Phloem Pericycle
Ranunculus acris - buttercup
Endodermis
Cortex
Phloem
Meta-xylem
Endarch: protoxylem is inside the metaxylem
Exarch: protoxylem is outside the metaxylem
Proto-xylem
Pericycle √

11. Protosteles: haplostele actinostele plectostele dicot root
Specialized Versions
haplostele
actinostele
plectostele
cortex phloem xylem
dicot
root
siphonostele
solenostele
dictyostele
cortex phloem xylem pith
leaf gap
leaf trace
monocot
root
eustele
atactostele
dicot stem
monocot stem

12. Symplastic Apoplastic
©1996 Norton Presentation Maker, W. W. Norton & Company

13. The endodermis is thus responsible for selective mineral uptake.
xylem inside
cortex outside
minerals cannot go between cells
The endodermis is thus responsible for selective mineral uptake.
minerals must go through cells
cell membrane proteins (active transporters) determine which minerals may be taken up
suberin-
waxy barrier
to apoplastic
movement

14. Mineral uptake: Active transport against concentration gradient
cell membrane
cell wall
too expensive?
Calcium transport protein
ADP + Pi
Ca2+
Ca2+
Ca2+
ATP
water flow
cytoplasmic solutes
more concentrated
soil solutes more dilute
Water potential low
Water potential high
Osmosis: passive movement of water from pure to polluted area

15. Root Anatomy: Dicot Root Cross Section
Epidermis - root hairs, mineral and water intake
Cortex - storage, defense
Endodermis - selective mineral uptake
Casparian strips in radial walls
Pericycle - lateral root formation (periderm)
(Vascular Cambium - makes 2° tissues)
Xylem - conduct water and mineral upwards
Phloem - CH2O delivery from leaves
One Vascular Cylinder (Phloem + (Cambium) + Xylem)
Radial Xylem-Phloem Arrangement
Exarch Xylem Maturation
Tetrarch (this example)

16. Monocot Root Cross Section Pith Xylem/Phloem Arr? Xylem Maturation?
______arch?
Smilax-catbrier

17. How is this section different?
Smilax - catbrier

18. A closer look…
What do these features tell you?
Starch
Cutin/Suberin
Mitochondria
Sieve Tube Element
Companion Cell
Vessel with Lignin
Xylem Parenchyma
Lignified Pith Parenchyma

19. What is the Pericycle doing?
Root Cap
Growing out through cortex
Zone of Cell Division
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

20. But shrubs also generally have some compromise for uprooting forces…feeder roots extending laterally.
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!

21. 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.

22. http://www. oxc. com. hk/raoul_nathalie/gallery/images/04%20Buttress

23. Prop roots such as these inspired flying buttresses.
Pandanus utilis - screw pine

25. Avicennia germinans (black mangrove)
pneumatophores