Chapter 39 Plant Responses to Internal and External Signals Flashcards
What are the plant hormones? (8 things)
- Auxin
- Cytokinins
- Gibberellins
- Abscisic Acid
- Ethylene
- Brassinosteroids
- Jasmonates
- Strigolactones
What are the major responses for auxin? 2 things
- Stimulates cell elongation
- regulates branching and organ bending
What are the major responses for cytokinins? 3 things
-Stimulates plant cell division
- promote later bud growth
- slow organ death
What are the major responses for gibberellins? 3 things
- Promote stem elongation
- Help seeds break dormancy
- Use stored reserves
What are the major responses for abscisic acid? 2 things
- Promotes stomatal closure in response to drought
- Promotes seed dormancy
What are the major responses for ethylene? 1 thing
- Mediates fruit ripening and the triple response
What are the major responses for brassinosteroids? 2 things
- Chemically similar to the sex hormones of animals
- Induce cell elongation and division
What are the major responses of jasmonates? 2 things
- mediate plant defenses against insect herbivores
- Regulate wide range of physiological processes
What are the major responses for strigolactones? 2 things
- Regulate apical dominance, seed germination, and mycorrhizal associations.
- suppress adventitious root formations
What are some environmental stresses?
- drought
- flooding
- salt
- heat
- cold
What are the major response from drought stress?
- ABA production
- reducing water loss by closing stomata
What are the major response of flooding stress?
- Formation of air tubes that help roots survive oxygen deprivation
What are the major response of salt stress?
- Avoiding osmotic water loss by producing solutes tolerated at high concentrations
What are the major responses to heat stress?
- Synthesis of heat-shock proteins that reduce protein denaturation at high temps.
What are the major responses to cold stress?
- Adjusting membrane fluidity
- avoiding osmotic water loss
- producing antifreeze proteins
What is etiolation?
Morphological adaptions for growing in the dark
What is de-etiolation?
Shoots and roots growing normally after being exposed to light
What are the 3 steps of cell signal processing?
- reception
- transduction
- response
What happens during reception?
- Internal and external signals are detected by receptors, proteins that change in response to specific stimuli
What is a phytochrome?
A receptor that’s capable of detecting light during de-etiolation
What happens during transduction?
Second messengers transfer and amplify signals from receptors to proteins that cause responses
What are the two important second messengers? What do they do?
- Ca2+ ions and cyclic GMP (cGMP)
- Ca2+ channels open up and levels increase in the cytosol when phytochrome responds to light
- This activates an enzyme that produces cGMP
What happens during response?
A signal transduction pathway leads to regulation by either transcriptional regulation or post-translational modification
What happens during transcriptional regulation?
- Specific transcription factors bind directly to specific regions of DNA and control transcription of genes (activators or repressors)
What happens during post-translational modification?
- Post-translational modification involves modification of existing proteins via phosphorylation of specific amino acids
What functions does enzymes de-etiolation activate do?
- function in photosynthesis
- Supply the chemical precursors for chlorophyll
- Affect the levels of plant hormones that regulate growth
What are plant hormones?
Chemical signals produced in low concentrations that modify or control one or more specific physiological processes within a plant
What is tropism?
Any response resulting in curvature of organs toward or away from a stimulus
What is phototropism?
A plant’s response to light
Where is auxin produced?
Produced in shoot tips and is transported down the stem
What is the most common auxin in plants?
Indoleacetic acid (IAA)
What is auxin’s role in cell elongation? 3 things
- Auxin stimulates proton pumps in the plasma membrane
- Proton pumps lowers cell wall’s pH which activates expansions
- Expansions (enzymes that loosen the wall’s fabric) cause the cellulose to loosen which prompts elongation
What is auxin’s role in plant development? (5 things)
- Polar transport of auxin plays a role in pattern formation of the developing plant
- Reduced auxin flow from the shoot of a branch stimulates growth in lower branches
- Auxin transport plays a role in phyllotaxy, the arrangement of leaves on the stem
- Polar transport of auxin from leaf margins directs leaf venation pattern
- The activity of the vascular cambium is under control of auxin transport
What is a practical use for auxin?
- auxin indolbutyric acid (IBA) stimulates adventitious roots and is used in vegetative propagation of plants by cuttings
How does cytokinins have anti-aging effects?
- By inhibiting protein breakdown
- stimulating RNA and protein synthesis
- Mobilizing nutrients from surrounding tissues
How do cytokinins, auxin, and strigolactone work together?
- By controlling the apical dominance which is the terminal bud’s ability to suppress development of axillary buds –> once removed, plant is bushier
How do cytokinins and auxin work together?
By controlling cell division and differentiation
How does gibberellins help the embryo?
Their release after water is imbibed, signals for seeds to germinate
What does abscisic acid do for a plant?
- Slows plant growth
How does early germination or seed dormancy broken?
- Dormancy is broken if ABA is removed by heavy weather
- Early (precocious) germination happens if there’s inactive or low levels of ABA
What happens if there is ABA accumulation?
The stomata will close rapidly
What are the effects of ethylene? 4 things
- mechanical stress
- senescence
- leaf abscission
- fruit ripening
What is the triple response?
Consists of slowing of stem elongation, thickening of the stem, and horizontal growth
What is senescence?
The programmed death of cells or organs
What is apoptosis (ethylene association)?
Programmed destruction of cells, organs, or whole plants
What is leaf abscission?
A change in the balance of auxin and ethylene in which a leaf falls from stem
How does ethylene trigger ripening?
- A burst of ethylene production triggers ripening process which furthers the release of more ethylene
How can fruit producers control ripening?
- By picking green fruit
- Controlling ethylene levels
What does brassinosteroids slow down and promote?
- slows down leaf abscission
- promote xylem differentiation
What are the two important jasmonates?
- Jasmonate (JA)
- Methyl Jasmonate (MeJA)
What are some physiological processes that Jasmonates regulate? 5 things
- Nectar secretion
- Fruit ripening
- Pollen production
- Flowering time
- Seed germination
What is photomorphogenesis?
Effect of light on plant morphology
What is action spectrum?
A graph that depicts relative response of a process to different wavelengths
What are the 4 things plants are able to detect in regards to light?
- light presence
- light direction
- light intensity
- wavelength (color)
What are the two major classes of light receptors?
- Blue light photoreceptors
- Phytochromes
What does blue-light photoreceptors control?
- Hypocotyl elongation
- Stomatal opening
- Phototropism
What are phytochromes? (red light)
- Photoreceptors responsible for opposing effects of red and far-red light
What does red light do? What does far-red light do?
- Red light: Increases germination
- Far Red Light: Inhibits germination
What does red light and far-red light trigger?
Red light: P(r) to P(fr)
Far-red Light: P(fr) to P(r)
What is photoperiodism?
Physiological response to photoperiod
What are short-day plant?
Plants that flower when a light period is shorter than a critical length
What are long-day plants?
Plants that flower when a light period is longer than a certain number of hours
What are day-neutral plants?
Plants that is controlled by plant maturity, not photoperiod
What is gravitropism?
Plant’s response to gravity
What are statoliths?
Dense cytoplasmic components
What do roots show for gravitropism? What do shoots show for gravitropism?
Roots: Positive gravitropism (moving with gravity)
Shoots: Negative gravitropism (moving against gravity)
What is thigmomorphogenesis?
The changes in form that result from mechanical disturbances
What is thigmotropism? What does in occur in?
- Growth in response to touch
- Occurs in vines and other climbing plants
What are the 7 levels of plant defenses against herbivores?
- Molecular
- Cellular
- Tissue
- Organ
- Community
- Organismal
- Population
What is an example of molecular-level defenses?
Chemical compounds that are produced to deter attackers
What is an example of cellular level defenses?
Cells specialized to form trichomes, which store chemical deterrents or produce irritants
What are tissue-level defenses?
- Leaves may be toughened with sclerenchyma tissue
What is an example of organ-level defenses?
Leaves are modified into spines and bristles; stems into thorns.
- Leaves mimic partially eaten leaves and/or structures that mimic insect eggs
What is an example of organismal level defense?
Plants may respond to attack by altering flowering time
What is an example of community level defense?
Plants “recruit” predatory animals that help defend against specific herbivores
What is an example of population level defense?
- Release of chemicals in response to herbivore attack which triggers defense responses of other plants
- Other plant species synchronously produce massive amounts of seeds after long intervals
What is herbivory?
Animals eating plants
What does systemic acquired resistance cause?
Causes systemic expression of defense genes and is a long-lasting response
What happens during systemic acquired resistance?
Methylsalicylic acid is synthesized around infection site and carried to other remote area via phloem.
At phloem, salicylic acid is produced and triggers the defense system to respond rapidly to another infection
What are the 3 functions of the hypersensitive response?
- Causes cell and tissue death near the infection site
- Induces production of enzymes that attack the pathogen
- Stimulates changes in the cell wall that confine the pathogen
What is the plant’s first line of defense?
The barrier that consists of the epidermis and periderm
What does the first line of immune defense depend on?
The plant’s ability to recognize pathogen-associated molecular patterns (PAMPs)
What are effectors?
Pathogen-encoded proteins that cripple the host’s innate immune system
What does the second level of plant immune defense consist of?
Consists of the response to pathogens and effectors
