Please enable JavaScript.
Coggle requires JavaScript to display documents.
Roots (Other Types of Roots and Root Modifications (Prop Roots (Buttress…
Roots
Other Types of Roots and Root Modifications
Lateral roots
Most common, generalized type
Comprising some or all roots in most plants
In some other plant
Roots are modified and carry out different roles
Storage roots
In biennial species
Carbohydrates stored at the root
Used to produce new shoot in the spring
Roots are the only permanent organ
Annual plants survive without storage capacity
Perennial plants
Permanent shoots
That do not die back
Store significant amounts of nutrients
During winter
Being subterranean
Roots are less available as food
Much more stable environment
Subject to less extreme changes in temperature
Important for survival of storage parenchyma cells
Prop Roots
Roots are capable of growth through the air
Act like stabilizers
Buttress roots
Tall, plate-like
Upper side grows more rapidly than other sides
Brace trunk against being blown over
Aerial Roots of Orchids
Orchids are epiphytic
Living attached to the branches of trees
Pull water out of roots when water is scarce
Valamen
Comprised of several layers of dead cells
Acts as waterproof barrier, not allowing water to leave
Contractile Roots
After extending through soil
Uppermost portion slowly contract
Changes in the shapes of cortex cells
More common than generally appreciated
Important for keeping stems at proper depths
Mycorrhizae
Seed plants that have relationship with soil fungi
Both organisms benefit
Ectomycorrhizal relationship
Fungal hyphea penetrate between the outermost root cortex cells
Never invade the cell itself
Nearly all woody forest plants
Endomycorrhizal association
Herbaceous plants
Hyphae penetrate the root cortex
As far as the epidermis
Cannot pass the Caspairian strip
Root Nodules and Nitrogen Fixation
Scarcity of nitrogenous compounds in soil
Main growth limiting factors
Plants have no enzymes to use nitrogen from the air
Conservation of atmospheric nitrogen into usable compounds
Nitrogen fixation
Nitrogenous compounds available by dead plants
Infection threat
Bacteria sits in it
Bacterium attaches to the convex and pushes into cell
Form a root nodule
Enters plant cell cytoplasm
Haustorial Roots of Parasitic Flowering Plants
Haustoria
Very little root like structures remain
Must adhere firmly to their hosts
Roots of Strangler Figs
Birds eat fruits from these
Deposit seeds onto other trees
Kills host
Internal Structure of Roots
Root cap
#
To remain in place, provide protection for apical meristem
Must have a specific structure and growth pattern
Root is growing through the edges
When first formed at the base
Cells are small and meristematic
When pushed forward
Develop dense starch grains
Endoplasmic reticulum displays to forward end of cell
Detect gravity
Root Apical Meristem
If examined in relation to root tissue it produces
Regular files of cells can be seen to originate in meristem
Extend into the regions of mature root tissue
More orderly than shoot
It experiences no disruption
Because of:
Leaf primordia
Leaf traces
Auxillary buds
Mitotically inactive region
Quiescent center
Cells are more resistant to various types of harm
They act primarily as a reserve of healthy cells
Zone of elongation
Cells expand greatly
#
Cells begin to differentiate into a visible pattern
Although none are mature
Tissues are all quite permeable
Zone of Maturation/Root Hair Zone
Several process occur simultaneously
Root hairs grow outward
Greatly increasing absorption of water and minerals
Zone of elongation merges gradually
Cortex cells continue to enlarge
Transfer of minerals from epidermis to vascular tissue
Endodermis
Minerals do not have access to the vascular tissue
The innermost layer of cortical cells differentiate into cylinder
Tangential walls
Closest to the vascular tissue or cortex
Radical walls
Top, bottom and side
Casparian strips
Bands of altered walls
Control types of minerals that enter xylem water stream
Pericycle
Between the vascular tissue and endodermis
Parenchyma cells
Constitute an irregular region
Lateral roots initiated here
#
Mature Portions of the Root
Root hairs
Only function for several days
Die quickly and degenerate
Passage cells
Cells that have only Casparian strips
Slow to develop
Root pressure
Absorption of minerals in the root hair zone
Causes powerful absorption of water
Water pressure
External Structure of Roots
Organization of Root Systems
Roots must have an enormous adsorption surface
Highly branched root system
Most seed plants have a single prominent taproot
Much larger than all the rest
Numerous small lateral roots or branch roots
Develops from the embryonic root
Radicle
Lateral roots
#
Taproots
Can become prominently swollen
Most monocots, some eudicots
Have a mass of many similarly sized roots
Fibrous root system
Adventitious roots
Increase absorptive and transport capacities of root system
Occurs from radicle dying during germination
Structure of Individual Roots
Root hair zone
Root hairs
#
Form only in the part of the root that is not elongating
Increase roots surface area
Many epidermal cells extend out as trichomes
Behind zone of elongation
Zone of elongation
#
Cells undergo division and expansion
Only a few millimeters long
Just behind the root cap and apical meristem
Root cap
Dictyosomes
Secrete a complex polysaccharide
Mucigel
Rich in carbohydrates and amino acids
Lubricates passage of root through soil
Constantly worn away
Renewed by cell multiplication
A thick layer of cells
Protects apical meristem
Root tip
Region where growth in length occurs
Fairly simple
No leaf axils or axillary buds
No leaves or leaf scars
Origin and Development of Lateral Roots
Lateral roots
Initiated by cell divisions in pericycle
Some roots become more densely cytoplasmic
Smaller vacuoles and resume mitotic activity
By the time emerging
Formed root cap
First protoxylem and protophloem element differentiate
Establishing a connection to the vascular tissue
Differs from bud formation in shoots
Initiated deep within the root
Endogenous origin
Formed in mature regions of root
Never develop into flowers
