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Roots (Other types of roots and root modification (Roots of Strangler Figs…
Roots
Other types of roots and root modification
Storage Roots
store carbohydrates
carbs produce a new shoot
have a more stable enviroment
store parenchyma cells
Prop Roots
Extensive growth through the air
do not make contact with soil
transport nutrients and water
acting as a stablizer
butress roots
air chamber
Aerial Roots of Orchids
dangle freely in the air
adapted to drought conditions
velamen does not permit water to leave
Contractile Roots
upmost portion roots slowly contract
the stem is pulled downward
the roots shorten and expand rapidly
keep stems at a proper depth
Mycorrhizae
soil fungi and plants benefit
ectomycorrhizal relationship
fungal hyphae penetrate outermost cortex cell
endomycorrhizal association, hyphae penetrate root cortex but not the casparian strip
form arbuscule
some hyphae fill with membranous vessels
Root Nodules and Nitrogen Fixation
nitrogen fixation
the chemical change of atmospheric nitrogen to usable compounds
bacteria
cause root hairs to curl
pushes into the cell
infection thread
penetrates the inner cortex
form a root nodule
plant cells fill with bacteria cells
convert N2 to nitrogenous compounds
the bacteria and plant co-evolve
Parasitic, Bacteria benefit (cross link)
Haustorial Roots of Parasitic Flowering Plants
roots of parasitic plants
adhere firmly to host
penetration through dermal system
makes contact with xylem
may or may not carry out own photosynthesis
Roots of Strangler Figs
root cling to bark
grows rapidly downward
absorbs nutrients from rainfall
root reaches soil
encircle tree's trunk
host tree finally dies
External Structure
Organization of Root Systems
Radicle
taproot- main root
Eudicots
lateral roots
adventitious roots
fibrous root system
increase absorptive and transport capacities
Monocots
Structure of Individual Roots
root tip- region of growth
localized growth
root cap- protect root apical meristem
the lateral root emerges a root cap that protects the root (cross link)
root cap secretes mucigel
Zone of elongation
Root hair zone
root hair
extract water and nutrients
Internal Structure
Root Cap
Cells closest to root meristem
forming cells that are pushed forward
Cells to the edge
grow toward side
Cells develop dense starch grains
Root Apical Meristem
Quiescent Center
mitotically inactive
resistant of harmful agents
root cap is damaged
quiescent center becomes active
Zone of Elongation
cells began to differentiate
protoderm becomes epidermis
provascular tissue becomes primary xylem and phloem
older, larger cells become metaxylem and metaphloem
ground tissue becomes root cortex
Zone of Maturation/ Root Hair Zone
Root hairs grow outward
Max absorption of water and minerals
Cortex cells
transfer of minerals
intercellular space
apoplastic transport
endodermis
thin cell walls
casparian strip
pericycle
parenchyma cells between vascular tissue and endodermis
Mature Portions of the Root
Root hairs die
absorption of water and mineral are reduced
Passage cells
have only casparian strip
Casparian Strip is to protect most inner cells (cross link)
endodermis maturation
sheath around vascular tissue
Root pressure
powerful absorption of water
Origin and Development of Lateral Roots
lateral roots
cell division of pericycle
small root primordium
primordium swells and breaks endodermis
lateral root emerges a root cap
lateral roots develop from roots
