Chapter 39 - Plant Responses To Internal And External Signals Flashcards
What are plant hormones?
Chemical signals that modify or control one or more specific physiological process within a place; at very low concentrations plant hormones can have a profound effect in plant growth and development depending on the amount, concentration, and combination of different hormones.
What is a hormone?
A signaling molecule that is produced in low concentrations by one part of an organism’s body and transported to other parts, where it binds to a specific receptor and triggers responses in target cells and tissues.
What are the major responses if Auxin?
Stimulates cell elongation
Regulates branching and organ bending
At higher concentrations, may inhibit cell elongation by inducing production of ethylene.
Phototropism and leaf abscission
What is phototropism?
The growth of a shoot toward light or away from it
What is Auxin?
A chemical substance that promotes elongation of coleoptiles produced predominantly in shoot tips and moves only from top to base.
What are the major responses to Cytokinins?
Stimulate plant cell division
Promote later bud growth
Slow organ dominance
What is apical dominance?
The ability of the apical bud to suppress the development of a ill art buds
What are the major responses to Gibberellins?
Promote stem elongation
Help seeds break dormancy and use stored reserves
Larger fruits
What are the major responses to ethylene?
Mediates fruit ripening and the triple response
Abscission
How does the action of ethylene work?
Enzymatic breakdown of cell walls makes fruit soft.
Ripening = positive feedback ( ethylene triggers ripening and ripening triggers more ethylene)
What is gravitropism?
Response to gravity
Where is gravitropism seen?
Positive gravitropism is seen in roots ( more auxin = less cell elongation)
Negative gravitropism is seen in shoots (more auxin = more cell elongation)
What are statoliths?
Dense cytoplasmic components that settle under the influence of gravity to the lower portions of the cell.
What is thigmotropism?
Directional growth in response to touch
What is thigmomorphogenesis?
Changes in form that result from mechanical perturbation (i.e. wind)
How do plants respond to dry environments (drought)?
Drought avoiders: grow in shade
Xerophytes: plant’s that need very little water; minimize water loss but take in less CO2 meaning less photosynthesis and slower growth.
How do xerophytes conserve water?
Thick waxy leaves and epidermal hairs to reduce evaporation
Stomatocrypts reduce transpiration
Leaf adaptations to dry environments?
Thick, water conserving leaves = succulents
Only grow when water is available = ocotillo
Spines (stem does photosynthesis; reflects solar radiation) = cactus
Root adaptations to dry environments?
Taproot system = deep roots that search for water deeply
Shallow root system = roots grow horizontally
What are alternate strategies responding to dry environments?
Reducing surface area of leaves (roll up leaves to reduce evaporation)
Hang downward to avoid direct sunlight (ie eucalyptus)
Accumulate proline and other solutes in vacuoles (ie xerophyte)
Why are hot environments bad for plants?
Heat can denature proteins
Adaptations to responses for hot environments?
Similar to dry environments
CAM plants have a specialized form of photosynthesis found in succulents that allows photosynthesis at night.
Why are wet environments bad for plants and what are some adaptations?
Soil may lack airspace meaning less oxygen for the roots.
Adaptations: shallow, slow growing roots, pneumatophores (come out of water to get oxygen like snorkels)
Why are salty environments bad for plants?
Lower water potential and salt is toxic to plants. Halophytes can live here.
What are adaptations for salty environments?
- Restricting the entry of toxic ions at root level (exclusion)
- Transporting the toxic ions to stem, leaf sheath or older leaves (plant level compartmentation)
- Excretion is salt through salt glands, salt-hairs or bladders (in most halophytes)
- Sequestration of the toxic ions to vacuole or cell wall - cell level compartmentation
What is a plant’s first line of defense against infection?
The barrier presented by the epidermis and periderm (mechanical defense)
Pathogens can enter through wounds or natural openings (ie stomata)
What is PAMP-Triggered immunity?
Depends on the plant’s ability to recognize pathogen associated molecular patterns (molecular sequences that are specific to certain pathogens)
Starts a chain is signaling events (protein extension, blocking of plasmodesmata, Lignin: mechanical barrier and toxic precursor) leading to the production of antimicrobial chemicals (phytoalexins) and toughen plant cell walls with Lignin
What is the Hypersensitive response?
A localized and specific, short term response that causes cell and tissue death near the infection sight, induces the production of enzyme that attacks the pathogen, stimulates changes in the cell wall that confine the pathogen.
What is system acquired resistance?
Causes systemic expression of defense genes and is long lasting and nonspecific response.
Methylsalicylic acid is synthesized around the infection site and carried in the phloem to other remote sites where it is converted to salicylic acid which triggers the defense system to respond rapidly to another infection.
What are some defenses against herbivores?
Physical defenses (thorns and trichomes) and chemical defenses (distasteful/toxic compounds)
What are molecular level defenses?
Chemical compounds including terpenoids, phenolics, and alkaloids can be produced to deter attackers - called secondary metabolites
(BT is a natural insecticide)
What are some chemical defenses?
They have no role in primary plant functions and are often secondary metabolites that attack the nervous system of insects
ie: atropine, cocaine, codeine and morphine, tetrodotoxin, nicotine, and erythromycin which we use as an antibiotic
Cellular level defenses?
Cells may be specialized to form trichomes which store chemical deterrents, or produce irritants like raphides which are common in dung cane
Tissue level defenses?
Leaves may be toughened with sclerenchyma tissue ie. artichoke
Organ level defenses?
Leaves can be modified into spines and bristles; stems can become thorns; some species have leaves that appear partially eaten (making herbivores think the “good parts” are gone); some have structures that mimic insect eggs to turn off herbivores from eating or other insects from laying eggs.
Organisms level defense?
Plants may respond to attack by altering flowering time
Population level defenses?
Some plants release chemicals in response to herbivore attack that trigger defense responses in nearby members of population
Community level defenses?
Some plants “recruit” predatory animals that help defend against specific herbivores
Ex. Parasitic wasps inject their eggs in caterpillars attacking the plant
