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Roots (Root Modifications (Prop Roots (mangroves (subterranean portion (no…
Roots
Root Modifications
Storage Roots
long term for carbs
produce new shoot in spring
annual plants dont need
Prop Roots
in soil
contract slightly
#
act as stabilizer
secondary growth
can become very strong
no breaking
no sagging
banyan trees
massive trees
roots become tall
buttress roots
upperside grows rapidly
brace the trunk
against wind
mangroves
selectively advantageous
subterranean portion
no O2
cortex
wide aerenchyma
Aerial Roots of Orchids
epiphytic
living attached to branches
roots spread along bark
epidermis
#
"Velamen"
layers of large dead cells (white)
waterproof barrier
Contractile Roots
more contraction than prop roots
caused by changes in
cortex cell shape
more common
Mycorrhizae
symbiotic relationship
ectomycorrhizal relationship
woody forest plants
fungal hyphae
penetrate cortex but never invade cell
endomycorrhizal association
herbaceous plants
hyphae penetrate root cortex
cannot pass casparian strip
#
root nodules
remain simple
complex
meristematic region
vascular tissue
endodermis
represent symbiosis
benefit
bacteria
#
without complex development does not occur
plant
not damaged
Nitrogen fixation
no enzyme system to use it
conversion
ATM N to usable compounds
symbiotic relationship
bacteria
secrete
causes root hairs to curl
tube
"Infection thread"
extends and forms root nodule
#
Haustorial Roots
parasitic plants'
highly modified
Haustoria
little root like structure remains
firmly to host
secreting adhesive
growing around
External Structures
lateral roots
"branch roots"
numerous
small
taproot
develops from embryonic roots
radicle
may produce more later roots
fibrous root system
monocots
eudicots
radicle dies
adventitious roots
not radicles
do not arise from pre-existing roots
increase absorption and transport capacities of root system
root cap
thick layer of cells
protects root apical meristem
dictyosomes
secrete
mucigel
lubricates passage of root through soil
rich in carbohydrates
foster rapid growth of soil bacteria
rich in amino acids
behind root cap
#
zone of elongation
few mm long
cells undergo
division
expansion
behind
root hair zone
epidermal cells
extend out
trichomes
root hairs
form in part of root that is not elongating
increase surface area
Internal Structures
root cap
#
provide protection
cells
meristematic
small
root apical meristem
quiescent region
mitotically inactive central region
resistant to harm
reserve of healthy cells
form new apical meristem
zone of elongation
#
behind root apical meristem
no cells mature
protoxylem
provascular tissue
closest to meristem
tissues are permeable
protophloem
outermost cells
protoderm
short zone
little absorption occurs
#
zone of maturation/root hair zone
grow outward
increasing absorption of h2o
minerals
no free access
vascular tissues
inner most layer
cortical cells
endodermis
#
cylinder
tangential walls
1 more item...
radial walls
1 more item...
bands alt walls
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zone of elongagtion
#
merges
cortex cells enlarge
between
#
#
parenchyma cells
pericycle
#
lateral roots
#
absorbtion
h20
root pressure
Origin & Development of Lateral Roots
initiated by cell divisons
in pericycle
densely cytoplasmic
smaller vacuoles
activity
root primordium
organizes into
root apical meristem
#
pushes outward
swells into cortex
#
endodermis
rip
root cap forms
#
undergo cell division
deep within
endogenous
axillary buds
superficial
