Lecture 3- Exploiting Light Flashcards
Silphium laciniatum
compass plant,grows leaves to face E and W, leaves move in late morning to keep away from hot midday sun
Phototropism
chloroplasts movement in response to light
Heliotropism
movement with sun, plants keeping track of sun
2 requirements for seeds of temperate grasslands and weeds to germinate
- seed must be buried for some time
2. seed needs exposure to light
light signal transport to nucleus
light to cytoplasm to signal to nucleus
Nucelopore
proteins at entrance that screen compounds
3 Types of barrier that nuclear membrane is
physical, chemical, energy driven
Nuclear membrane energy-driven
entrance and exit, uses GTP instead of ATP
Running out of GTP
plant cell dies, human cell gets diseases
Light receptor molecules
all are proteins
Types of receptors to blue or UV wavelengths
cry-1, cry-2, phototropin
Types of receptors to red/far-red wavelengths
phytochromes
Phytochrome movement
induced by light, moves from cytoplasm into nucleus
Blue light receptor protein movement
only found within nucleus, only move within nucleus
5 Types of Phytochromes
PHYA, PHYB, PHYC, PHYD, PHYE
Phytochrome synthesis
in the dark, at time of manufacture in cell they are produced in inactive form (Pr), ready to absorb red light
Phytochrome exposure to red light
Changes shape to phyiologically active form (Pfr) which moves into nucelus, found by studies with flourescnet tag
PhyA abundance
dark-grown plants
Location of Pr form of PHYA
cytoplasm, sticking to outer edge
What happens when Pfr moves into nucleus
alters gene expression
Nuclear Localization Signal
code that is part of PHYA a.a sequence, allows PHYA to pass through nucleopore into nucleus. recognized by nucelopore proteins
PHYA signal cascades in cytoplasm
very low fluence response (moonlight response)
high irradiance response (short pulses of intense light)
continuous red light response (uninterrupted red light) (only in experimental conditions)
PHYB
receptor for classical red/far red responses, has NLS
Red light wavelength
650-670nm
Far-red light wavelength
705-740nm
Reversal of effect of red light
far-red light
Germination occurs if
last light was red
No germination if
last light was far-red
Red:far-red on forest floor,growth form
red<far-red, tall and thin
Red:far-red in the open, growth form
1:1, squat and branched
Light perception
PHYB
Malvastrum rotundifolium
spotted mallow. leaves face rising sun, follow sun during day, return to original position at night
plants that move to follow sun
sunflower, soybean, cowpea, cotton
Harnessed plants experienced
lower leaf temp, fewer/smaller seeds
How does Pfr turn back to Pr
protein turnover and enzymatic degradation
Pfr degrades faster than Pr
autoconversion of Pfr to Pr
Neutral
day length insensitive, tomatoes and dandelions flower all season
long day plants
only flower if number of hours of daylight/day exceeds threshold.
lettuce and spinach flower in spring (longer days)
Short day plants
only flower if # of hours of daylight/day is less than certain number
eg soybeans and chrysanthemums flower in late summer (shorter days)
Harry Allard and Wightman Garner experiment
Biloxi soybeans-5 weeks earlier
Maryland Mammoth tobacco-3 months earlier
Pigeon pea (Cajanus cajan)
short day plant, genetically altered to lose shortday requirement
Chrysanthemum
short day plant, flowering delayed by flashes of light in night. daylength altered with blackout curtains to produce them year round
