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Ch. 7 Roots (Other Types of Roots and Root Modifications (Storage Roots…
Ch. 7 Roots
Other Types of Roots and Root Modifications
Storage Roots
stored carbohydrates
annual plants can't live without it
perennial plants
permanent shoots
store significant amounts of nutrients
Prop Roots
#
transport additional nutrients and water
buttress roots
brace trunk from blowing over
Aerial Roots of Orchids
epiphytic
attached to branches of trees
velamen
layers of large dead cells (white)
waterproof barrier
Contractile Roots
contractions
caused by changes in shape of cortex cells
shorten and expand radically
Mycorrhizae
ectomycorrhizal relationship
woody forest plants
fungal hyphae penetrate between root cortex
endomycorrhizal association
herbaceous plants
hyphae penetrate root cortex as far as endodermus
Root Nodules and Nitrogen Fixation
nitrogen fixation
conversion of nitrogen into usable compounds
infection thread
penetrates one cell after another
tubelike invagination
root nodule
bulb-like structures
Haustorial Roots of Parasitic Flowering Plants
haustoria
parasitic plants become highly modified
Tristerix
spends life being diffuse root system
network of parenchyma cells
Roots of Strangler Figs
penetrate soil and branch rapidly
roots fuse together
Internal Structure of Roots
Root Cap
protect root apical meristem
4-5 days
Root Apical Meristem
quiescent center
mitotically inactive central region
Zone of Elongation
just behind root apical meristem
tissues are permeable
Zone of Maturation/Root Hair Zone
#
root hairs grow outward
merges with zone of elongation
cortex cells enlarge
transfer of minerals
endodermis
innermost layer of cortical cells
Casparian strips
bands of altered walls
pericycle
parenchyma cells
Mature Portions of the Root
passage cells
only Caparian strips
root pressure
powerful absorbtion of water
Origin and Development of Lateral Roots
lateral roots
root cap
protoxylem and protophloem differentiate
connection to the vascular tissues
differs from buds
deep within root
formed in mature regions
never develop flowers
Concepts
Three Functions
anchoring plant
plants remain upright for fruit, pollinators
blown from sites
absorbing water and minerals
cylindrical shape
producing hormones
cytokinin and gibberellin
Taproots
#
Carrots, Beets, Radishes
main site of carbohydrate storage
External Structure of Roots
Organization of Root Systems
taproots
lateral root
branch root
radicle
largest root
monocots (some eudicots)
fibrouse root system
adventitious roots
increase absorbative and transport capacities
Structure of Individual Roots
root apical meristem
root cap
protection
mucigel
zone of elongation
root hair zone
root hairs
increase root structure
few millimeters
Where lateral roots form
both contract
more about lateral roots
