Roots Flashcards
What are the function of roots?
• Anchorage • Absorption–water&mineralsinsolution • Storageofwater/food • Specialised: – ‘breathing’ – vegetative spread – climbing – contractile – support: aerial, prop, buttress • producehormones(GAs,ABA,cytokinins)
More about roots?
• Radicle–embryoroot
• almostallseedlingsdeveloparootsystemmore rapidly than the shoot system – why?
• Dicots–taprootsystem
– primary root/s + secondary roots
• Monocots–fibrousrootsystem – many roots similar diameter
– adventitious roots – from the stem
Primary Root Structure
Primary root structure
• The 4 zones along the root tip:
• i) the root cap
• ii) region of cell division – root apical meristem
• iii) region of elongation
• iv) region of maturation/differentiation
What is the root cap?
Root Cap – outer cells ‘rubbed off’ – 4 to 5 days after production – continual replacement from inside • Perception of gravity - amyloplasts • Covers root tip • Protection
Where is the region of cell division ?
Region of cell division
• root apical meristem – Gk ‘meristos’ divisible
• other apical meristem/s is located ……..? • lateral meristems are ……………?
Where is the Protoderm found?
Epidermis
Where is the Ground Meristem found?
Cortex
Where is the Procambium found?
Xylem & Phloem
Where is the Region of Elongation?
Region of elongation • cells inc. length several times • cell diameter little change • start of vacuolation • some vascular differentiation – – which would form first – X or P??? • pushes root cap + apical meristem thru soil • would root hairs form in this region? Why?
Where is the Region of Maturation?
Region of maturation • moving from outside to inside – epidermis (with root hairs) – cortex – endodermis – innermost cortex layer – pericycle – xylem & phloem • epidermis • has cuticle, but very thin
What are Root Hairs?
• Roothairs – tubular extensions of epidermal cells – are not multi-cellular, are not ‘mini-roots’ – massive increase in root surface area – numerous (38,000 1 x 1 cm) – short (
What is the Cortex?
Cortex • between epidermis and stele • mainly parenchyma (storage) • air spaces common • innermost layer is the endodermis
What is the Endodermis?
Endodermis
• radial and transverse walls have suberised ‘rings’
• known as Casparian strips
– named after German botanist Robert Caspary
• suberin is water proof
– also found in bark & abscission zones
• water normally travels thru cell walls (apoplast)
• CS forces ‘water’ across plasma membranes, into the symplast
• plant can regulate minerals absorbed
What is the vascular cylinder (or Stele)?
• Vascular cylinder (or stele)
• Outermost layer: the pericycle
– one layer thick, parenchyma – very important, involved in:
• vascular cambium initiation • cork cambium initiation
• lateral root initiation
What are Later Roots?
- Lateral roots
- initiated in pericycle
- opposite X arms
- push/dissolve their way thru cortex • therefore directly ‘plumbed’ into X • if initiated in the epidermis …….
Vascular Tissues In Dicots?
- Vascular tissues – dicots & gymnos
- solid core of xylem
- usually 3 – 5 arms of xylem
- star-shaped in TS
- phloem between arms
- vas. camb. betn X & P
- secondary growth by VC linking (see diag.)
- VC is first lobed, becomes circular
- cork cambium (if present) init. in pericycle
- epidermis and cortex lost
Vascular Tissues In Monocots?
• Vascular tissues – monocots
• large parenchyma pith
• ring of X alternating with P in outer stele
– like the chainring or sprocket on a bicycle • no VC
Specialised Roots?
Specialized roots
• Food-storage roots
– most roots are storage roots, some specialised
– e.g. carrots, beetroot, radish, sweet potatoes, etc
• Water-storageroots • Propagative roots
– roots near soil surface produce suckers
– suckers come from adventitious buds
– ‘adventitious’: arising where not normally found – buds usually from leaf axils
– suckering – e.g. Tree of Heaven (Rocky Hill)
What are Pneumatophores?
• Pneumatophores
– breathing roots in mangroves, have lenticels – water contains little air
– roots need air for respiration
What are Aerial Roots?
• Aerial roots
– velamen roots in orchids
– prop roots in corn, banyan trees, etc – ‘climbing’ roots in Ivy
What are Contractile Roots?
• Contractile roots
– pull bulbs/corms deeper into the soil – related to temp./H20/fire ???
What are Buttress Roots and Parasitic Roots?
• Buttress roots – tropical trees, for stability • Parasitic roots – some spp. spend all their life below gnd – except for flowering – no chlorophyll – form haustoria on host plants – e.g. broomrape in CSU garden beds
