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CHAPTER 7: ROOTS, root zones, developing lateral root - Coggle Diagram
CHAPTER 7: ROOTS
Other Types of Roots and Root Modifications
Contractile Roots
after extending through soil and becoming anchored
uppermost portions contract
stem is pulled downsward
keeps stems at proper depth
Mycorrhizae
symbiotic relationship with soil fungi
mycorrhizae
ectomycorrhizal relationship
nearly all woody forest plants
fungal hyphae penetrate between outermost root cortex cells
endomycorrhizal association
hyphae penetrate root cortex as far as endodermis
cannot pass through Casparian strip
#
branch repeatedly
arbuscule
granules of phosphorus
take starch grains
herbaceous plants
Aerial Roots of Orchids
epiphytic
attached to branches of other trees
rainforests
adapted to
drought conditions
velamen
(root epidermis)
waterproof barrier
Root Nodules and Nitrogen Fixation
scarcity of nitrogen in soil
growth-limiting factor
nitrogen fixation
legumes
symbiotic relationship with nitrogen-fixing bacteria
infection thread
into root's inner cortex
root nodule
released from infection thread
fills plant cells with bacteroids
bacteria fixes nitrogen
plan supplies sugars
leghemoglobin
protects bacterium from oxygen
This is just me thinking, but could this someday become it's own organelle like mitochondria or chloroplasts
endosymbiosis
Prop Roots
some roots grow through the air
prop roots grow through the air
act as stabilizers after reaching the ground
as well as absorption
supports long branches
buttress roots
brace trunk against wind
tropical trees
aerial portion can be used for gas exchange and respiration
intertidal regions
mangrove trees
Haustorial Roots of Parasitic Flowering Plants
roots of parasites
haustoria
must adhere firmly to host
secrete adhesive
grow around small branch or root
penetration
connects to xylem of host
Storage Roots
carbohydrate storage
used to produce new shoot in the spring
biennial and perennial plants
Roots of Strangler Figs
epiphytes perched on branch of host tree
roots cling to bark of host
grow rapidly and hug trunk of host
absorb nutrients from rainwater
roots reach soil
penetrate rapidly
branch profusely
upper portions become woody
roots branch
encircle host tree's trunk
fuse to each other where they meet
encases trunk of host
host tree dies
Internal Structure of Roots
Zone of Elongation
#
behind apical meristem
cells expand greatly
begin to differentiate
protoderm
provascular tissue
protoxylem and protophloem
metaxylem and metaphloem
uniform parenchyma
cortex
permeable tissues
Zone of Maturation / Root Hair Zone
#
root hairs grow outward
no distinct boundary between this and zone of elongation
transfer of minerals from epidermis to vascular tissue
endodermis differentiates
Casparian strips
control minerals that enter xylem
vascular tissues
larger cells become fully differentiated and functional
mass of xylem surrounded by phloem
no pith
pericylce
between vascular tissue and endodermis
lateral roots are initiated in pericycle
Root Apical Meristem
#
mitotically active
mitotically inactive central region
quiescent center
backup meristem in case apical meristem or root cap is damaged
which happens a lot
Mature Portions of the Root
#
root hairs only function for a few days
endodermis maturation
passage cells
layers of suberin and lignin
watertight sheath
root pressure
Root Cap
#
cells closest to meristem are meristematic
dense starch grains to detect gravity
constantly regenerating itself
Concepts
main functions
absorbing water and minerals
cylindrical shape
producing hormones
ratio of shoot to root control
gibberellin
cytokinin
anchoring plant to substrate
stability
additional functions
taproots
carbohydrate storage
shoot buds
new plants
spines
hold-fasts
parasitic
Origin and Development of Lateral Roots
#
lateral roots initiated by cells in pericycle
root primordium breaks through endodermis
emerges with root cap and proto-vascular elements
External Structure of Roots
Organization of Root Systems
highly branched root system
prominent taproot (usually larger)
develops from embryonic root (radicle)
numerous lateral roots
produces more lateral roots
fibrous root system
mass of similarly sized roots
more root primordia initiated
adventitious roots
growth forms
eudicots
secondary growth
trunk has more conduction capacity
increases leaf and root size
monocots
no secondary growth
does not increase leaf or root size
stolons and rhizomes
adventitious roots
Structure of Individual Roots
root tip
growth occurs
apical meristems
longitudinal growth
root cap
pushes through soil
must be renewed
mucigel
lubricant
helps ion diffusion
protects meristem
zone of elongation
zone of maturation
root hair
increase surface area
can fit in smaller pores
region where new lateral roots emerge
Plants and People and Having a Weight Problem
storing food for winter
animals
store as fat
lightweight
good for movement
deciduous plants
store as starch
long-term stability
roots
potatoes, carrots, etc.
exceptions
pollen
drop of oil
lighter and easier to carry
seeds
store oil
lighter and smaller
