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Roots (Other types of roots and root modification (Prop roots (Buttress…
Roots
Other types of roots and root modification
Storage roots
Long-term storage for carbohydrates
Carbohydrates stored are use to produce a new shoot in spring
Prop roots
Exposed roots
Roots grow through the air
Place additional tension on the stem to stabilize it
Buttress roots
Upper side grows more rapidly than other parts
Aerial roots of orchids
Roots spread along the surface of the bark and dangle freely in the air
Contractile roots
Upper portions of root contract after extending into the soil
Pull the stem downward so the base of the shoot is kept at soil level
Mycorrhizae
Symbiotic relationships between roots
Ectomycorrhizal relationship
Fungal hyphae penetrate woody forest plants
Endomycorrhizal association
Hyphae penetrate herbaceous plants
Root nodules and nitrogen fixation
Nitrogen fixation
Chemical conversion of atmospheric nitrogen into usable compounds
Root nodule
Formed when cortical cells undergo mitosis
Haustorial roots of parasitic flowering plants
Highly modified roots
Must adhere firmly to host by adhesion or attachment
Inadequate for growth in soil
Roots of strangler figs
Cling to bark of the host tree branch and grow rapidly downward
Internal structure of roots
Root cap
Cells are small and meristematic when first formed
Cells develop dense starch grains & ER becomes displaced to front end of cell
Root apical meristem
More orderly than the stem
Quiescent center
Mitotically inactive central region
Make the root more resistant to radiation and toxic chemicals
Zone of elongation
Some meristematic activity
Most cells are enlarging
Cells differentiate but are not mature
Tissues are very permeable
So that minerals can pass through
Zone of maturation/root hair zone
Root hairs grow outward
Zone of elongation merges with zone of maturation
Endodermis
Not accessible to minerals
Casparian strips
Control types of minerals that enter the xylem
Mature portions of the root
Passage cells
Cells that are slow to mature and only have Casparian strips
Concepts
Roots have three functions
Anchor the plant
Absorb water and minerals
Produce hormones
Taproots
Plants main site for storage of carbohydrates during winter
Origin and development of lateral roots
Initiated by cell divisions in the pericycle
Small root primordium swells into cortex
Root pushes outward and destroys cells of cortex and epidermis
External structure of roots
Organization of root systems
Lateral roots (branch roots)
Numerous small roots coming off of the main taproot
Radicle
Embryonic root that forms the taproot
Fibrous root system
Mass of many similarly sized roots
Adventitious roots
Do not arise on pre-existing roots
Increase absorption and transportation
Structure of individual roots
Root cap
Protects root apical meristem
Mucigel
Polysaccharide that lubricates passage of the root through soil
Zone of elongation
Cells undergo division and expansion
Root hair zone
Epidermal cells extend out as narrow trichomes
Root hairs
Form in part of root that is not elongating