Light Flashcards
Photomorphogenesis
effects of light on plant morphology
phototropism
directional growth in response to light
What do plants detect
light direction, intensity, and wavelength
Action spectrum
depicts relative response of a process to different wavelengths
What are the classes of light receptors
Blue-light photoreceptors and phytochromes
Blue-light photoreceptors
control hypocotyl elongation
Control stomatal opening
Control phototropism
Phytochromes
Pigments that regulate many of a plant’s responses to light throughout its life
Seed germination
shade avoidance
Etiolation (shoot elongation)
what system provides the plant with information about the quality of light
phytochrome system
Shaded plants receive far more _____ than ____ light
far-red, red
Shade avoidance response
the phytochrome ratio shifts in favor of Pr when a tree is shade
Circadian rhythms
cycles that are about 24 hours long and are governed by an “internal clock”
What may the internal clock depend on
synthesis of a protein regulated through feedback control and may be common to all eukaryotes
Photoperiod
the relative lengths of night and day
what is the environmental stimulus plants use most often to detect time of year
Photoperiod
Phytochrome conversion
marks sunrise and sunset, providing the biological clock with environmental cues
Photoperiodism
a physiological response to photoperiod
Short-day plants
Flower when light period is shorter than a critical threshold
Long-day plants
flower when a light period is longer than a certain number of hours
Day-neutral plants
flowering is controlled by plant maturity, not photoperiod
what are short-day plants governed by
whether the critical night length sets a minimum number of hours of darkness
what are long-day plants governed by
whether the critical night length sets a maximum number of hours of darkness
Flowering Locus C (FLC)
Discovered in Arabidopsis thaliana FLC activation inhibits flowering MADS box gene Controls vernalization Epigenetic control regulates the gene Cold exposure reduces expression
florigen
the flowering signal
what are florigens
may be a macromolecule governed by the CONSTANS gene
what must happen for a bud to form a flower instead of a vegetative shoot
meristem identity genes must first be switched on
Gravitropism
Response to gravity
what kind of gravitropism do roots show
positive gravitropism
what kind of gravitropism do shoots show
negative gravitropism
statoliths
specialized plastids (amyloplasts) containing dense starch grains
what may contribute to gravity detection
dense organelles, in addition to starch granules
Thigmomorphogenesis
refers to changes in form that result from mechanical disturbance
Thigmotropism
movement of ions induces osmotic potential change
What are the responses to drought
reduce transpiration by closing stomata slow leaf growth reduce exposed surface area growth of shallow roots is inhibited deeper roots continue to grow
Response to flooding
enzymatic destruction of root cortex cells creates air tubes that help plants survive oxygen deprivation during flooding
Response to herbivory
thorns and distasteful or toxic compounds
Some plants “recruit” predatory animals that help defend against specific herbivores
Responses to high temps
produce heat shock proteins (HSPs) if exposed to rapid temperature increases
Can survive otherwise lethal temperatures if they are gradually exposed to increasing temperature
HSPs
stabilize other proteins
Thermotolerance
the gradual exposure of plants to high temperatures
Responses to chilling
Lipid composition of a plant’s membranes can help predict whether the plant will be sensitive or resistant to chilling
Supercooling - survive as low as -40 C
Limits ice crystal formation to extracellular spaces
Antifreeze proteins
The more unsaturated the membrane lipids are,
the more resistant the plant is to chilling
