Root Structure and Function - plant physplantphys.info/plants_human/lecpdf/root.pdf1/20/11! 1! Root...
Transcript of Root Structure and Function - plant physplantphys.info/plants_human/lecpdf/root.pdf1/20/11! 1! Root...
1/20/11
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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 differentiation Protoderm Ground Meristem Provascular
Zone of Cell Elongation - cell expansion
Zone of Cell Division - new cells by mitosis
Root Cap - penetration, padding
Mucilage Slough Cells
Root Tip Senses Gravity Auxin Hormone Produced Auxin Accumulates on Lower Growth Inhibited on Lower… Relative to Upper Root 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
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?
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Root Vascular Cylinder and Cortex Ranunculus acris - buttercup
Cortex
Endodermis
Xylem
Phloem
Pericycle
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)
Monocot Root Cross Section
Smilax-catbrier
Pith
How is this section different? Smilax - catbrier
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
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
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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 pine Prop 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