Roots Flashcards
What are 6 functions of roots?
- Absorb water and nutrients
- Conduct water and minerals to the shoots
- Anchor and support the shoots
- Storage
- Sense and respond to environmental stimuli
- Coordinate symbiotic relationships with microorganisms in the rhizosphere
What are the 5 types of roots?
Radicle Primary root Lateral roots Feeder roots Adventitious roots
What is a radicle?
Embryonic root
What is a primary root?
Mature radicle
What is a lateral root?
Roots that grow out from the primary root
What is a feeder root?
The first 10 cm of a root that is in contact with the nutrient rich areas of the soil
What is an adventitious root?
Roots that grow from non-root tissues
What are the 2 types of root systems? What plants are they commonly found in?
Fibrous: more common in monocots
Taproot: common in eudicots
What is the structure of the vascular tissue in roots?
Found in the middle. The xylem and phloem is contained in the stele in the centre of the root, surrounded by the pericycle
What is the stele?
The vascular cylinder that runs through the centre of the root
What is the pericycle?
Tissue surrounding the stele that can develop into lateral roots
How do lateral roots develop?
The pericycle develops into the root primordia, which pushes through the cortex and breaks through the epidermis
What two root structures are made of ground tissue?
Cortex and endodermis
What is the cortex?
All the tissue that surrounds the vascular cylinder
What is endodermis?
Inner most layer of the cortex, regulates entry into vascular cylinder
What feature is found on the endodermis cells?
The casparian strips in the cell walls
What do the casparian strips do?
Waxy layer that is completely impermeable to water. Forces water from the apoplastic route to the symplastic route so everything coming in has to cross a cell membrane at least once
What are the 3 regions of a root?
The root apical meristem, the zone of elongation, the zone of maturation
What happens in the root apical meristem?
Cell division, but no cell growth or differentiation
What do cells of the lower layer of the root apical meristem become?
The root cap. Older cells get pushed off and newer cells replace them
What do cells of the middle layer of the root apical meristem become?
Precursors of dermal and ground tissue
What do cells of the upper layer of the root apical meristem become?
Vascular tissue
What is the root cap?
Cells that cover the growing root tip
What does the root cap do?
Protects the apical meristem, produces mucigel, and responds to environmental stimuli
What is mucigel? What does it do?
A gel made of polysaccharides and water. It lubricates the root tip to make it easier to get through the soil and creates a favourable environment for particular microbes
Which part of the root tip is responsible for sensing environmental stimuli?
Columella
What sort of stimuli does the columella sense?
Gravity, moisture gradients, chemical gradients, vibrations and sounds
What part of the root tip communicates information about environmental stimuli to the rest of the plant?
The transition zone
How does the transition zone communicate information?
Electrical signals that are equivalent to action potentials
What happened in the experiment with the pea plant with its roots in the two pots?
When there were enough nutrients in the pot with constant nutrients to complete the life cycle, the plant put most of its roots in there. If there wasn’t enough, it put most of its roots in the pot with variable nutrients instead
What happens in the zone of elongation?
Cells elongate and some of the ground meristem divides. Parts of the cortex start to mature and the sieve tube members mature
What happens in the zone of maturation?
Cells mature and differentiate and stop elongating. Root hairs develop
Why does no movement occur in the zone of maturation?
Would destroy the root hairs
What are 7 specialized roots?
Adventitious, prop, epiphytic, pneumatophores, contractile roots, storage roots, haustoria (parasitic roots)
How do monocots form the fibrous root system?
Adventitious roots that grow from the bottom part of the embryonic stem
What are nodal roots?
Involved in vegetative reproduction. Little shootlets grow adventitious roots
If not part of their normal life cycle, why would plants grow adventitious roots?
Stress response to drought or flood or wound response
What are prop roots for?
Mechanical support and aiding really long branches in water absorption
What is an epiphyte?
A plant that grows on another plant
What are the challenges for epiphytes?
Hard to get nutrients, water, and mechanical support when you aren’t in the soil
What modification do epiphytic roots have? How does it help them?
A velamen, which is a thicker modified epidermis. It adheres to substrates and sucks up any water like a sponge
What plants use pneumatophores?
Plants growing in water saturated, anaerobic soils. Like mangroves
How do pneumatophores work?
They grow up like a snorkel and collect air for the roots under ground
Where are contractile roots found? What do they do?
Found in a lot of bulbs. They contract and pull the bulb down when it gets too high up in the soil and starts photosynthesizing
What do storage roots store?
Starch. Stores it in grains called amyloplasts
What are the 2 types of mycorrhizae?
Ectomycorrhizae and arbuscular mycorrhizae
How do ectomycorrhizae associate with plants?
Their hyphae go through cell walls and intracellular spaces and forms a sheath around the root
How do arbuscular mycorrhizae associate with plants?
Form arbuscules inside the cell and exchange nutrients, water and photosynthates
Why is forming associations with fungi and bacteria good for the plant?
Plants have higher rates of photosynthesis than they actually need, so they often secrete photosynthates into the soil and support entire ecosystems while getting nutrients for their troubles
What is the “wood-wide web”?
A network of arbuscular mycorrhizae that connects plant roots
What can be exchanged between plants through mycorrhizal networks?
Nutrients and defence compounds
Is rhizobia a functional or taxonomic classification?
Functional, the bacteria aren’t related
What plant family do rhizobia associate with?
Fabaceae
How do Fabaceae plants form associations with rhizobia?
Nitrogen stressed plants send out a chemical signal that is perceived by bacteria, which produce Nod factors in response. The Nod factors are sensed by the root hairs, and causes the plant to switch off its defence systems and envelop the bacteria in shepherd’s crook structure. The bacteria get brought into the plant and it builds them a nice little anaerobic house in the epidermis and cortex
