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Roots (Other Types of Roots and Root Modifications (Storage Roots…
Roots
Other Types of Roots and Root Modifications
Storage Roots
carbohydrates
used to produce new shoot in spring
permanent organs in biennial species
beets
carrots
celery
permanent organs in many perennials
Datura
Phlox
daisies
Prop Roots
extensive growth through air
may take months to reach ground
once ground is reached transport nutrients
act as stabilizers
buttress roots
tall
plate-like
brace the trunk
Aerial Roots of Orchids
epiphytic
attached to branches of trees
adapted to drought
velamen
root epidermis
waterproof barrier
Contractile Roots
roots firmly anchor in soil
uppermost portions contract
stem is pulled downward
root surface becomes wrinkled
Mycorrhizae
symbiotic relationship w/ soil fungi
ectomycorrhizal relationship
fungi hyphae penetrate b/t root cortex cells
endomycorrhizal association
fungi hyphae penetrate root cortex to caspian strip
invade the cell
do not break plasma/ vacuole membrane
Root Nodules and Nitrogen Fixation
scarcity of nitrogenous compounds in soil
main growth limiting factor
nitrogen fixation
prokaryotes use N₂ in the air
die and decompose=available to plants
symbiotic relationship
nitrogen-fixing bacteria (Rhizobium)
infection thread
penetrates to roots cortex
bacterium enters cytoplasm
proliferates and becomes known as bacteriods
plant and microbe benifit
root nodule
simple
complex
Haustorial Roots of Parasitic Flowering Plants
number of angiosperms are parasites
substrate in the body of another plant
haustoria
highly modified roots
secrete adhesive
grow around branch/root
penetrate by forcing shaft of cells through host dermis
make contact with xylem
carry out own photosynthesis
contact phloem and perform little/no photosynthesis
Roots of Strangler Figs
roots cling to bark of host tree
grow rapidly downward
hug the tree trunk
months-years roots do not contact soil
penetrate soil rapidly once reached
encase host tree trunk
host tree dies and rots away
strangler fig becomes self supporting tree
Internal Structure of Roots
Root Cap
meristematic
files of cells pushed forward
detect gravity
starch grains settle to lower side of cell
simultaneously cells on edge
grow toward side
proliferate
Root Apical Meristem
quiescent center
mitotically inactive
believed to be a reserve for healthy cells
resistant to harmful agents
if apical meristem/ root cap damage
quiescent center cells become active
form new apical meristem
Zone of Elongation
cells expand greatly
cells are enlarging
differentiation
protoderm
epidermis
provascular tissue
primary xylem/ primary phloem
ground tissue
root cortex
Zone of Maturation/ Root Hair Zone
root hairs grow outward
increasing water absorption
endodermis
tangential walls
encrusted with lignin and suberin
waterproof the endodermis
known as Casparian strips
pericycle
between vascular tissue and endodermis
initiate lateral roots
Mature Portions of the Root
passage cells
only casparian strips
suspected slow development
root pressure
External Structure of Roots
Organization of Root Systems
enormous absorptive area
highly branched root system
lateral roots
branched roots
taproot
develops from radicle
embryonic root
carrots
beats
turnips
fibrous root system
similarly sized roots
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adventitious roots
increase absorbtive and transport capacities
Structure of Individual Roots
fairly simple
root tip is region of growth
apical meristem
protected by root cap
dictyosomes
secrete mucigel to lubricate passage of root
through soil
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thick layer of cells
renewed by cell multipilication
zone of elongation
just behind root cap
cells undergo division and expansion
root hair zone
behind zone of elongation
epidermal cells extend out
narrow trichomes
root hairs
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no leaves
no leaf scars
no leaf axils
no axillary buds
Origin and Development of Lateral Roots
initiated by cell division in pericycle
small root primordium
organizes into root apical meristem
pushes outward
breaking through endodermis
forms root cap
protoxylem/ protophloem differentiate
