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Roots, Roots (Storage roots (permanent organs in biennial species (celery,…
Roots
Roots
Storage roots
Carbohydrates
used to produces new shoot in spring
permanent organs in biennial species
celery
beets
carrots
permanent organs in many perennials
Datura
Phlox
Daisies
extensive growth through air
may take months to reach ground
once ground is reach
act as stablizers
buttress roots
Tall plates like and brace trunk
Aerial roots of orchids
Epiphytic
attached to branches tree
adapted to drought
Adapted to drought
velamen
root epdermis
Water proof barrier
Contractile roots
roots firmly anchor in soil
stem is pulled dowward
root surface becomes wrinkled
uppermost portions contract
roots of strangler figs
roots cling to bark of host tree
hug the tree trunk
grow rapidly downward
penetrate soil rapidly once reached
encased host tree trunk
host tree dies and decomposes
Strangler fig becomes self supported
Other Types of Roots and Root Modifcation
Mycorrhizae
symbiotic relationship with soil fingi
Ectomycorrhizal relationship
fungi hyphae penetrate b/t root cortex cells
endomycorrhizal association
fungi hyphae penetrate root cortex to caspian strip
invade cell
do not break plasma vacuole
Root Nodules and Nitrogen Fixation
scarcity of nitrogenous compounds in the soil
main growth limiting factor
Symbiotic relationship
nitrogen fixing bacteria (Rhizobium)
infection
penetrates to roots cortex
bacterium enters cytoplasm
proliferates
becomes bacteriods
plant and microbe benefit
root nodule
complex
simple
nitrogen fixation
prokaryotes use N2 in the air
die and decompose available for plants
Haustorial Roots and Parasitic Flowering Plants
Number of angiosperms are parasites
substrate in the body of another plant
haustoria
highly modified roots
grow around branch roots
make contact with xylem
secrete adhesive
External Structure of roots
Organization of root systems
enormous absorptive area
branched roots
highly branched root system
develops from radicle
embryonic root
carrots
beets
turnips
Taproot
similar sized roots
fibrous root system
adventitious roots
increase absorbtive and transport capacities
lateral roots
Adventrous roots
increased absorption and transport capabilites
Structure of individual roots
no leaves
no leaf axils
no leaf scars
no axillary buds
fairly simple
root tip region of growth
apical merstem
thick layer of cellls
renewed by cell multipilcation
dictyosomessecrete mucigel to lubricate passage through soil
rich in carbohydrates
amino acids
fosters rapid growth of bacteria
release of nutrients from the soil
protected by root cap
just behind root cap
cells under go divison and expansion
zone of elongation
behind zone of elongatior
narrow trichromes
root hairs
form where root is not elongating
penetrate small pores in soil
Origin and Development of lateral roots
initiated by cell division
small root primordum
organizes in the root
pushes out
protoxylem protophloem differentiate
forms root cap
breaking through endodermis
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
proliferate
grow toward side
Root Apical Meristem
quiescent center
mitotically inactive
if apical /root cap damage
quiescent center cells become active form new apical meristem
believed to be a reserve for healthy cells
resistant to harmful agents
Zone of Elongation
cells expand greatly
epidermis
cells are enlarging
differentiation
ground tissue
provascular tissue
root cortex
primary xylem/ primary phloem
Zone of Maturation/ Root Hair Zone
pericycle
between vascular tissue and endodermis
initiate lateral roots
endodermis
tangential walls
encrusted lignin and suberin
waterproof the endodermis
known as Casparian strips
root hairs grow outward
increasing water absorption
Mature Portions of the Root
passage cells
only casparian strips
suspected slow development
root pressure
Forced shaft of cell through host dermis
