Photoperiodism Flashcards
Explain the difference between long day
plants, short day plants and day-neutral plants
Long day plants (eg, sunflowers) only flower when the day length exceeds the particular critical day length. These plants flower during summer.
Short day plants (eg, spinach) only flower when the day length is less than its particular critical day length. These plants flower during winter.
Day-neutral plants (eg, tomatoes) are not affected by the day length. These plants can flower any time during the year.
Critical day length: the period of daylight, specific in length for different species
Describe what phytochrome is
Phytochrome is a type of plant pigment. It has two forms: Pr or Pred and Pfr or Pfar red.
Explain the function of the two forms of
phytochrome
During the day, the red light is absorbed by the Pr and converted into Pfr. At night, when there is more “far red” light, Pfr is converted back into Pr. The levels of Pr and Pfr tell the plant when to flower.
Long day plants flower when the day is long so that enough Pfr builds up.
Short day plants flower when the day is short and the night is long so that there is more Pr.
Explain why it is important for plants to
flower at a certain time of day
Plants flowering at a certain time of day is important for reproduction. Plants want their seeds to germinate at the same time every year at the point when the chance of survival is the highest. If the flowers are pollinated by insects then the flowering would have to occur at a time when the insects are most active.
