1/20/11

1

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?

1/20/11

2

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

1/20/11

3

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