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Root (Other Types of Roots and Root Modifications (Prop Roots (Mangrooves,…
Root
Other Types of Roots and Root Modifications
Storage Roots
long term storage of carbohydrates
used to produce new shoots in autumn
more stable enviroment
survival of storage perichyma cells
Aerial root of orchids
spread along the surface of the bark
adapted to dry, arid environment
Prop Roots
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Mangrooves
helps in respiration
provides support against powerful water currents
buttress root
brace the trunk
prevents from wind from blowing it
upper side grows more rapidly
function
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transport nutrients and water to stem
act as stabilizers for stem
extensive growth through the air
Contractile roots
contraction caused by changes in cells shape of cortex
shoots becomes anchored to the soil
important in keeping stems at the proper depth
Mycorrhizae
symbiotic relationship between root and soil fungi
ectomycorrhizal
almost all woody forest plants
fungal hyphae invades the cells of the outermost cortex
endomycorrhizal
fungal hyphae penetrates upto endodermis
important for phosphorus absorption
Root nodules and nitrogen fixation
scarcity of nitrogen
growth limiting factor
plants cannot use atmospheric nitrogen, N2
Nitrogen fixation
conversion of atmospheric nitrogen into usable compound
Rhizobium
nitrogen fixing bacteria
symbiotic with legumes
Root nodule
cortical cell division in inner cortex
provides way for
Rhizobium
to enter cytoplasm
Haustorial roots of parasitic flowering plants
very little root-like structure remains
grow around the roots to adhere
Tristerix
spends most of its life growing inside cactus
Roots of strangler figs
roots do not contact soil for months
must absorb nutrients from rainwater
grows rapidly once it touches soil
Internal structure of roots
Root Cap
Function
protect apical meristem
Provide stability to the root
Cells
undergo cell division
small and meristematic when formed
differ as they push towards the side
Root apical meristem
more orderly than shoots
cell division occurs throughout
quiescent center
mitotically inactive
more resistant to radiation and toxic chemicals
reserve of healthy cells
become active when the apical meristem or root cap damaged
Zone of elongation
behind apical meristem
cells expand greatly and expand
similar to shoot subapical meristem
Protoderm
outermost cells
differentiate into epidermis
Provascular tissue
in the center
develop in to primary xylem and phloem
ground tissue
differentiate into root cortex
Larger, older cells
differentiate into metaxylem and metaphloem
Zone of maturation
root hairs grow outward
increase surface area
increase water and minerals absorption
cortex cells enlarge
transport minerals from epidermis to vascular tissue
endodermis
water proof cell wall
cylindrical
Casparian strips
bands of altered wall
control the flow of minerals
Mature portion of the root
root hair
dies and degenarate after several days
absorption of water/minerals greatly reduce
endodermis
unchanged
continue to mature
Passage cells
have only Casparian strips
slow to develop
Origin and Development of Lateral Roots
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initiated by cell divisions in the pericycle
root primordium
organize itself into apical meristem
push outwards
swells into cortex
causes endodermis to torn
new lateral root
invades the endodermis
destroys cells of the cortex and epidermis
complete lateral root
formed root cap
protoxylem and protophloem differentiate
establish connection to the vascular tissue of the parent root
External structure of Roots
Organization of root system
highly branched
seed plants
single prominant taproot
numerous small lateral roots
radicle
embroyonic root
give rise to taproot
fibrous root system
most monocots and some eudicots
radical dies during germination
adventitious roots
do not arise on pre-existing roots
increase absorptive and transport capacities
structure of individual roots
simple structure
root tip
growth in length occurs
longitudinal growth
by discrete apical meristem
extreme tips pushes through soil
mucigal
secreted by dictyosomes
lubricate passage of the root
causes soil to release nutrient ions
rich in carbohydrates and amino acids
foster rapid growth of microbes around the tip
Functional Connection
Mechanism Connection
Structural Connection
