Lecture 8 - Root Structure And Development Flashcards
The first structure to emerge from germinating seed.
Primary root
Root functions
Anchorage, absorption, storage, hormone production, secondary metabolite production
Anchorage
Holds plant in position and stabilizes it
Absorption
Water, minerals, gas exchange
Storage
Food from photosynthesizing parts moves through phloem to root
Food is used by the root but also:
Digested and transported back aboveground
Storage: Some roots are specialized for:
Overwinter storage
What hormones are produced?
Cytokinins and gibberellins
What do hormones do?
Stimulate growth and development
Where are hormones made and where are they transported?
Made in meristematic regions of root and transported upward in xylem
Secondary metabolite production example
Nicotine in tobacco
What is the rhizosphere?
Layer of soil bound to the root by mucigel and root hairs
What does the rhizosphere contain?
Micro-organisms and sloughed off rootcap cells
Rhizosphere: what is mycorrhizae?
Mutually beneficial symbiotic associations between fungi and plant roots
Plant benefit
Increased ability to get water and elements, protection
Fungus benefit
Carbohydrates and vitamins
Types of root systems
- Tap root
- fibrous root
Tap roots are most common in?
Dicots
What is the main component of taproots?
Primary root
Lateral roots are common in what?
Tap roots and fibrous roots
Fibrous roots are common in what?
Monocots
No one root is prominent
Fibrous roots
Describe the primary root of fibrous roots
Short and short-lived
Root design is dependent on:
Moisture, temperature, soil composition
What do feeder roots do?
Most of the absorption
Where are feeder roots located?
Upper soil layers
Growth of roots is continuous unless:
Adverse conditions
Balance between surface area for photosynthesis and absorption of water and minerals is balance between:
The root and shoot
Damage to the root will cause:
Damage to the shoot (and vice versa)
What does lack of water cause?
Root-produced hormones that slow down shoot growth
What does reduced shoot growth cause?
Decreases available carbohydrates so root growth is limited.
What is the root apex made of?
Root apical meristem and rootcap
What is the rootcaps function?
Protection
Rootcap: cells produce a slimy polysaccharide called?
Mucigel
Mucigel function
Lubrication
What happens to sloughed off cells of the rootcap?
Replaced by new ones from the root apical meristem
root apical meristem is subterminal, meaning its
Under the root cap
In the root apical meristem, files of cells (initials) divide, but do not
Differentiate
root apical meristem: quiescent Center
Contains initials that are inactive and will replace injured regions
Zones of root growth
root apical meristem, region of elongation, region of maturation
root apical meristem is the region of:
Cell division
Region of elongation is the region of
Cell expansion
In the Region of elongation, root growth is towards:
The tip
The Region of elongation increases:
Root length
Region of maturation is the region of:
Cell differentiation
Root hairs are present in which growth zone?
Region of maturation
What are trichoblasts?
- Root hairs
- unicellular extensions of epidermal cells
What zone do root hairs form?
Absorption zone
Describe the life span of root hairs
Short-lived and replaced by new ones
Cuticle is _________ in root hairs
Absent
Primary meristems formed by the root apical meristem
Protoderm, ground meristem, procambium
What does the protoderm form?
Dermal tissues - epidermis, root hairs
What does the ground meristem form?
Ground tissue - cortex
What does the procambium form?
Vascular cylinder: primary vascular tissues, pericycle
What makes up most of the root?
The Cortex
Cortex is made of mostly:
Parenchyma
What are plastids (of the cortex) role?
Store starch
Cortex contains numerous:
Intercellular spaces
Intercellular spaces allow for:
Free flow of material through the symplast
In some plants, what is the outermost layer of the cortex?
Exodermis
What is the location of the endodermis?
Innermost layer of cortex
Describe the endodermis
Compact, lacks air spaces
Has a casparian strip
Endodermis
What does the casparian strip contain?
Suberin or lignin in anticlinal walls
casparian strip function
Apoplastic barrier
casparian strip: How do substances enter and leave the vascular cylinder? What does this allow for?
Through protoplasts. Allows for selectivity
What forms the stele?
Xylem and phloem
Stele does not include
Secondary vascular tissue
Outermost layer of stele and its location
Pericycle, below endodermis
Simplest and most primitive type of stele
Protostele
Describe the core of a protostele
Solid Xylem core, ridge like projections
- phloem surrounds Xylem
- no pith
What kind of roots have protostele?
Dicot roots
Xylem and phloem form concentric cylinders around a central pith
Siphonostele
Where is phloem located in Siphonostele?
Outer surface of Xylem only or on both inner and outer surface of xylem
What kind of roots have Siphonostele?
Monocot roots
How many cell layers does the pericycle have?
Single cell layer
Outermost layer of stele
Pericycle
What is the pericycle made of?
Parenchyma cells
Region where lateral roots begin
Pericycle
In roots that undergo secondary growth, what does the pericycle form?
Vascular cambium and cork cambium
Lateral roots are referred to as:
Secondary roots
How do lateral roots arise?
From pericycle by periclinal cell divisions
Several lateral roots initiate:
Simultaneously
Have their own root cap, root apical meristem, and absorption zone
Lateral roots
Lateral roots can produce:
New lateral roots
Secondary growth increases:
Width of root
What plant type is secondary growth common in?
Woody plants
Secondary growth is produced by:
Lateral meristems
Secondary growth: vascular cambium produces:
Secondary xylem (inside) and secondary phloem (outside)
What is the vascular cambium initiated from?
Procombial cells between primary phloem and primary Xylem
Also contributes to vascular cambium
Pericycle
Where are rays produced?
In the secondary xylem and secondary phloem
Secondary growth: cork cambium initiates from:
Pericycle
Cork is produced towards:
Outer surface
Phelloderm produced toward
Inner surface
What does the periderm consist of?
Phelloderm, cork cambium, and cork
Lenticels allow
Gas exchange
Secondary growth: At the end of first years growth, these tissues are present in a woody dicot root
- Remnants of epidermis
- remnants of cortex
- periderm
- pericycle
- primary phloem fibers and crushed phloem cells
- secondary phloem
- vascular cambium
- secondary xylem
- primary Xylem
Modified root types
Aerial, stilt, epiphytes, pneumatophores, fleshy
How are aerial roots produced?
From aboveground structures
Some aerial roots are prop roots that function in? What is their function after making contact with soil?
Supporting the plant. Then, Absorption
Stilt roots seen in tropical trees provide
Support
Some aerial roots cling to surfaces to provide:
Climbing support
Non-parasitic plants that grow on other plants
Epiphytes
Epiphytes: Root epidermis is:
Several layers thick
Epiphytes: root Epidermis function
Protection, may function in water absorption
Air roots
Pneumatophores
Pneumatophores allow plants to grow where?
Swampy habitats
Pneumatophores contain
Large air-filled cavities, may have lenticels
Grow upward against gravity
Pneumatophores
Fleshy roots are specialized for:
Food storage
Have Storage parenchyma in Xylem and phloem
Fleshy roots
What are root nodules?
Swellings on roots of legumes inhabited by symbiotic nitrogen-fixing bacteria (ex rhizobium)
Bacteria provides plant with nitrogen it can use
Fix atmospheric nitrogen
Root nodules: Plant provides bacteria with
Carbohydrates
