9.1.4 - Phytochromes and flowering Flashcards
What are phytochromes?
A blue-green pigment inside plants that exists in interconvertible forms: Pr and Pfr
What is Pr?
A biologically inactive form of phytochrome that absorbs red light.
What is Pfr?
A biologically active form of phytochrome which absorbs far red light.
What wavelengths of light to Pr and Pfr absorb?
Pr = 660nm
Pfr = 730 nm
What happens between Pr and Pfr in an absence of red light?
The unstable Pfr gradually converts back into Pr
How long does the conversion take between Pr and Pfr in high and low light intensities?
Low light intensities = Minutes
High light intensities = Seconds
What form of phytochrome rises during the day and why does this happen?
Levels of Pfr rise.
Sunlight contains more wavelengths at 660nm than 730 nm so Pr is converted into Pfr.
What form of phytochrome rises during the night and why does this happen?
Levels of Pr rise.
Red wavelengths of light are not available and so as Pfr is unstable it converts back to Pr.
What is photoperiodism?
The reaction of plants to day length.
What do phytochromes do in long day and short day plants?
Long-day plants = stimulates flowering
Short-day plants = Inhibits flowering.
Give an example of a long day and short day plant.
Long-day = snapdragons
Short-day = Strawberries.
