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Roots (Other modifications of Roots and Root modifications (Contractile…
Roots
Other modifications of Roots and Root modifications
Storage roots
stored carbs produce new shoot in spring
roots have stable environment
Roots store nurtients
allows growth before leaves come
Prop Roots
capable of growth through air
20-50 cm
transport water to stem
secondary growth creates good support
important for trees in stormy climates
Aerial Roots or orchids
empiphytic
attached to trees
live in rainforests
velemen
acts as water barrier
keeps water from leaving
when dry, air could pull out water
Contractile roots
root fixed to siol
stem pulled downward
Vascular tissues buckle
keep some plants stem at a depth
Mycorrhizae
symbiotic relationship with fungi
woody forst plants
fungal cells penetrate the root cortex
Herbaceous plants
hyphae penetrate to endodermis
Rood Nodules and N Fixation
no enzymes in plants use N
rhizobium fixates N for legumes
Infection thread
where bacteria sits in root
Root nodule
contains N fixating bacteria
cells undergo mitosis
Haustorial Roots of Parasitic Flowering plants
haustoria
roots of parasitic plants
little root structure remains
Inadequate for soil growth
secrete adhesive or wrap around
penetration occurs by
penetrating dermis
cracking dermis
Roots of Strangler figs
epiphites
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birds eat their fruit
deposit seed on other trees
produces leaves that cover the host
prevents photosynthesis in host
Internal Structure of Roots
Root cap
meristematic cells
base of root cap
edge cells group together
cells pushed toward cap
develop dense starch
middle lamella breaks down
Root apical meristem
produces root tissues
cell files extend to center
quiescent center
mitotically inactive region
Zone of elongation
Cells expand greatly
similar to subapical meristem
protoderm
outermost cells
tissues are permeable
center cells
pro vascular tissue
Zone of Maturation
Root hairs grow outward
Increases absorbtion
Thin cuticle appears
transfer of minerals
Endodermis
tangenital walls
radial walls
walls that touch other cells
Allows O to diffuse to root
Casparian strips
controls minerals that enter xylem
impermeable
pericycle
between vascular tissue and endodermis
Initiates lateral roots
Mature portions of root
layer of suberin applied on radial
Passage cells
slow to develop
have only casparian strips
Endodermis continues to mature
watertight sheath around vascular tissue
powerful water absorb in root hair
causes root pressure
mature endodermis keeps water in
External structure of roots
Organization of root systems
Large absorptive surface
highly branched root system,
Most seed plants have taproot
Develops from embryonic root
Lateral Roots
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Produce more lateral roots
Become swollen like taproot
woody plants
undergo secondary growth
Fibrous root system
radicle dies
plant ages
more root primidoria initiated
Advantages roots
increase absorptive and transport capapbilities
monocots
cannot undergo secondary growth
increase size
stolons or rhizozomes
adventitious roots
Structure of individual roots
simple
No leaves or leaf scars
no leaf axials
no auxiliary buds
embedded in solid matrix
all parts can't grow at once
Root cap
protects root apical meristem
forced through the soil
worn away and renews
Mucigel
Lubricates root throug in soil
Makes soil release nutrients
rich in carbs and amino acids
Zone of elongation
cells undergo division, expansion
behind root cap
Root hair zone
behind zone of elongation
increase surface area
Origin and development of Lateral Roots
Lateral Roots initiated in pericycle
forms a cap root
protoxylem and protophloem elements differentiate
Initiated deep in root
never develop into flowers
Cytoplasmic density increases