chapter 39: plant responses to external signals Flashcards
What is sensed at the coleoptile tip?
light responsible for triggering phototropism
What does light do?
Cues many events in plant growth/development
What is photomorphogenesis?
Its the effects of light on plant morphology
What can plants detect?
direction, intensity and wavelength (color)
What is the action spectrum?
Graph that depicts relative response of a process to different wavelengths of light.
What do photoreceptors do?
mediate different plant responses
What are the two major classes of light receptors?
- blue-light receptors: control hypocotyl elongation, stomata opening and phototropism
- phytochromes: contains pigments absorbing mostly red light, regulating seed germination and shade avoidance
How does order of red and far-red illumination affect seed germination?
- red light increases germinations
- far-red light inhibits germinations
What do light and temperature regimes do?
Trigger oscillation
What is a photoperiod?
relative lengths of night and day (are environmental stimulus
What is photoperiodism?
Physiological response to photoperiod
What are the different types of plants in regards to light periods?
- short-day plants: light period is shorter than a critical length
- long-day plants: light period is longer than a certain number of hours
- day-neutral plants: controlled by plant-maturity, not photoperiod
What are the different types of plants in regards to critical night lengths?
- short-day plants: critical night lengths sets a minimum number of hours of darkness.
- long-day plants: critical night lengths sets a maximum number of hours of darkness.
What is vernalization?
cold pretreatment to induce flowering
what is florigen?
a hypothetical flowering signal molecule.
What are the different environmental circumstances using development/physiological mechanisms?
- phototropism: response to light
- geotropism: response to gravity
- chemotropism: response to chemical substances
- hydrotropism: response to water
- thigmotropism: response to mechanical stimulation
What is gravitropism?
Response to gravity
roots have a positive gravitropism
shoots have a negative gravitropism
What is thigmomorphogenesis?
changes in form that results from mechanical disturbance
What is thigmotropism?
Growth in response to touch
What are action potentials?
transmission of electrical impulses making a mechanical stimulation making rapid leaf movements
What are the two types of stresses?
- biotic stress: bacterial, fungi, viral pathogens, insects and nematodes
- abiotic stress: salinity, drought, light, temperature, nutrient deficiency
How do plants survive flooding?
enzymatic destruction of root cortex creates air tubes that help plants survive oxygen deprivation
How do plants survive droughts?
They reduce transpiration, by closing stomata, they reduce exposed surface are, and sometimes shed leaves. Shallow roots are inhibited from growing, but not deeper roots
What does evaporative cooling do?
Helps cool leaves (transpiration)
What do heat-shock proteins do?
They protect other proteins from heat stress
What does salt stress do and what is the cells response?
- it lowers water potential
- reduces water intake.
The cell then produces certain solutes at high concentrations which keeps water potential of cells more negative than soil solution
What does cold stress do and how do cells react?
- decreases membrane fluidity
- alters lipid composition of membranes
- freezing, ice forms in plants cell walls and intracellular spaces
Plants have antifreeze proteins that prevent ice crystal formation
What is herbivory?
animals eating plants
What are the defenses against herbivores?
- physical defense: thorns and trichomes
- chemical defense: distasteful or toxic compounds
- mind-altering effects: hallucinogenic and psychedelic
What are the line of defense against pathogens?
- barrier presented by epidermis and periderm
- immune responses where chemical attacks are aimed at isolating pathogen and preventing its spread.
What can pathogens that can deliver effectors do?
They can suppress PAMP-triggered plant immunity
What are effectors?
pathogen-encoded proteins
What is effector-triggered immunity?
its the action of 100 disease resistance (R) genes where each R protein is activated by specific effector
What are R proteins?
Protein that activates plant defenses and triggers signal transduction pathways
What are the 4 hypersensitive responses and what do they do?
- stomatal closure: prevents more pathogen cells to enter
- production of toxins: molecules targeted to pathogen
- reinforcements: neighbouring plant cell walls limit movement of pathogen
- suicide of cells: rapid in infected region
What does hypersensitive responses produce?
It produces a signal that indices systematic acquired resistance (SAR)
