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Chapter 7: Roots (Origin/Development of Lateral Roots (lateral roots…
Chapter 7: Roots
Origin/Development of Lateral Roots
initiated by cell division
located in the pericycle
cells become densely cytoplasmic
with small vacuoles
root primordium
swells into the cortex
lateral roots emerge
root cap has formed
then will form connections
to the vascular tissues
of the parental root
deep within the root
endogenous region
never develops into flowers
formed in mature regions
Internal Structures of Roots
root cap
cells are pushed to the cap
structure and metabolism change
endoplasmic reticulum becomes less conspicuous
starch grains are digested
cells
small
meristematic
first formed at the base
root apical meristem
extends in mature root tissue
root is more orderly
than the shoot
quiescent center
mitotically inactive central region
cells are resistant
to harmful agents
radiation
toxic chemicals
forms new apical meristem
zone of elongation
cells expand greatly
mostly enlarging
meristematic activity continues
outermost cells are protoderm
tissues are quite permeable
zone of maturation
also root hair zone
root hairs grow outward
merges with zone of elongation
no distinct boundaries exist
minerals don't have free access
to vascular tissues
endodermis
innermost layer of cortical cell
cylinder shaped
cells have tangential walls
radial walls
top walls
side walls
bottom walls
they all touch endodermis
encrusted with
lignin
suberin
casparian strip
bands of altered walls
involved in controlling
minerals
outer xylem water stream
cortex cells can't function this way
mature portions
passage cells
mature parts of the root
possible to find occasional cells
only have casparian strips
#
slow to develop
root pressure
due to absorption of minerals
created by water pressure
builds up
Other Types of Root/Root Modification
storage roots
provide long-term storage
for carbohydrates
used to produce new shoots
more stable environment
prop roots
does not make contact with soil
transport additional
nutrients
water
contract slightly
places tension on stem
acts as stabilizers
buttress roots
upper side grows more rapidly
braces the trunk
against wind damage
mycorrhizae
singular; mycorrhiza
roots of seed plants
have relations with fungi
benefits both organisms
two main types of relationships
ectomycorrhizal
all woody forest plants
fungal hypae
penetrate outermost root
endomycorrhizal
association
herbaceous plants
penetrates root cortex
root nodules/nitrogen fixations
nitrogen fixation
chemical comersion
atmospheric nitrogen
usable compounds
infection thread
a tube
bacterium sits on it
penetrates cell after cell
extends into cells inner cortex
root nodule
bacterium is released
from infection thread
adjacent cortical cells
undergoes mitosis
External Structures of Roots
Concepts
roots have 3 functions
anchoring plant to a substrate
absorption
water
minerals
producing hormones
Root Stem Organization
lateral roots
or branch roots
small roots from taproots
radicle
develops from embryonic root
present in the seed
after germination
fibrous root systems
mass of similar sized roots
located in some monocots
located in some eudicots
arises after radicle dies
after germination
#
may occur during as well
adventitious roots
don't arise on pre-existing roots
they are not radicles
increased absorption
in the root system
increased transport capacities
in the root system
Individual Root Structure
individual roots are simple
does not contain
leaves
leaf scars
leaf axils
axillary buds
root tip
growth in length occurs
root is embedded
in a solid matrix
root parts can't extend at once
root cap
protects root apical meristem
forced through the soil
ahead of the root body
renewal
by cellular multiplication
mucigel
dictyosomes of root cap cells
secrete complex polysaccharides
lubricates root passage
through the soil
rich in
carbohydrates
amino acids
zone of elongation
behind the root cap
few millimeters long
root hair zone
#
behind zone of elongation
region where the epidermal cells
extend out as narrow trichomes
root hair
forms in the root
that is not elongating
increases root surface area
can enter any crevice
extracts
water
minerals
takes place after germination
takes place after each other
mature portions only have casparian strips