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Ch 7 Roots (Other Types of Roots & Root Modifications (Roots of…
Ch 7 Roots
Other Types of Roots & Root Modifications
Storage Roots
long term storage
roots as permanent organs
biennial
beets
carrots
celery
perennials
Phlox
Datura
many daisies
Prop Roots
transport nutrients & water to stem
buttress roots
brace trunk
upper side grows faster
ex
ex.
Aerial Roots of Orchids
epiphytic
roots along surface of bark
dangle freely in the air
Contractile Roots
ex.
Gladiolus
Crinum
Oxalis
more contraction
important keeping stem @ proper depth
Mycorrhizae
2 relationships
ectomycorrhizal
never invade cells
fungal hyphae
penetrate root cortex cells
endomycorrhizal
hyphae
penetrate endodermis
cells cannot pass Casparian strip
Root Nodules and Nitrogen Fixation
nitrogen fixation
some prokaryotes use N2
later available to other plants
as nitrogenous compounds
infection thread
where bacteria sits
extends to root cortex
root nodule
simple or complex
Haustorial Roots of Parasitic Flowering Plants
haustoria
inadequate for growth in soil
very little root structure remains
ex.
Tristerix
Roots of Strangler Figs
grow as epiphytes perched on host tree
germinates from bird deposition
form tight network of branches on host
results in hosts death
Structure of Roots
External Structure
Organization of Root Systems
radicle
embryotic root
largest out of lateral roots
fibrous root system
monocots/eudicots
arises because radicle dies
adventitious roots
increase absorptive/transport capacities
not limited to monocots
do not rise on pre-existing roots
Structure of individual roots
mucigel
secreted by root cells
lubricates passage of root
root cap
thick layer of cells
protects the root apical meristem
Internal Structure
Root cap
small and meristematic cells
constantly regenerating
dynamic equilibrium
Root apical meristem
more orderly than the shoot
because of
leaf traces
axillary buds
leaf primordia
quiescent center
inactive central region
cells resistant to harmful agents
reserve of healthy cells
Zone of elongation
differentiate to visible pattern
protoderm cells differentiate to epidermis
Center: provascualar tissue develop to
primary xylem
primary phloem
older cells develop to
metaxylem
metaphloem
Zone of maturation/Root hair zone
endodermis
minerals have no free access to tissue
cortical cells differentiates here
Casparian strip
bands of altered walls
controls minerals that enter xylem
cells become fully differentiated & functional
metaxylem & metaphloem
Mature Portions of the Root
passage cells
once passageways
but suspected slow to develop
root pressure
water pressure from absorption
water/mineral absorption reduced
Concepts
root functions
anchoring the plant
absorbing water & subsrate
producing hormones
taproots
carrots
beets
radishes
main site of carb storage during winter
