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Roots (Other Types of Roots & Root Modifications (Aerial Roots of…
Roots
Other Types of Roots & Root Modifications
Myocorrhizae
symbiotic relationship with soil fungi
both organisms benefit
Root nodules and N Fixation
chemical conversion of atmospheric nitrogen into usable compounds
infection thread
a tubelike invagination of the plant cell wall
root notule
infection thread extends all the way into the cortex, and cells undergo mitosis
Contractile roots
roots that undergo more contraction than others
uppermost portions contract
more common than generally appreciated
Aerial Roots of Orchids
roots spread along surface of tree bark
often dangle free in the air
valamen
acts as a waterproof barrier permitting water to leave the sides of the root
Haustorial roots of flowering plants
haustoria
roots of highly parasitic plants that have become highly modified
very little root like structure remains
parasitic
Prop roots
roots growing through the air
after making contact with soil
they transport nutrients and water to stem
contract and place tension on stem
stabilizer
buttress roots
upper side grows more rapidly than other parts
roots of strangler figs
when seeds germinate, its roots cling to the bark of the host tree
for months/years, the roots have no contact with soil
must absorb rainwater that runs down the trunk of the host tree
can prevent host tree from growing bigger
branch and grow at various angles
Storage roots
provide long term storage for carbohydrates
these are used to produce a new shoot in the spring
Internal structures
Zone of elongation
just behind the root apical meristem
region where cells expand greatly
mostly cells are enlarging
tissues here are quite permeable
Zone of maturation/root hair zone
root hairs grow outward
increasing absorption of water and minerals
endodermis
innermost layer of cortical cells
cells have tangled walls
waterproof
casparian strips
involved in controlling the types of minerals that enter the xylem
pericylce
between the vascular tissue and endodermis
perenchyma cells
irregular region
lateral roots are initiated by this
Root apical meristem
files of cells originate here and extend into the mature root tissues
more orderly than the shoot
mitotically inactive region
quiescent center
these cells are more resistant to types of harmful agents
now believed these cells serve as a reserve of healthy cells
mature portions of the root
root hairs only function for several days
passage cells
once thought to be a passageway for the absorbtion of minerals
now thought to show development
root pressure
water pressure from the absorption of water and minerals by the root hairs
Root Cap
provides protection for the apical meristem
first cells are small and meristematic
then they develop dense starch grains
ER gets displaced to the forward end of cell
as cells are pushed, their structure and metabolism change
External Structures
Organization of root systems
enormous absorptive surface
lateral roots or branch roots
much larger than all the rest
develops from the radicle
may produce more lateral roots
monocots and eudicots
fibrous root system
mass of many similar sized roots
aka adventitious roots
Structure of individual roots
fairly simple
no leaf axils nor axillary buds
root tip is where growth occurs
apical growth
only extreme tip pushes through soil
apical meristem is protected by a thick layer of cells
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the root cap
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root cap cells secrete polysaccharides
mucigel
lubricates passage of the root through the soil
zone of elongation
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cells undergo division and expansion
root hair zone
trichomes
