Question

Differentiate between Pr form and Pfr form of phytochrome.

Answer 1

Hint: Phytochromes are a photoreceptor type used in light sensing plants, bacteria and fungi. They are susceptible to light in the red and far-rooted area of the spectrum, and can be identified by far-rooted light either Type I or Type II triggered by red light.

Complete answer:

Pr	Pfr
It is an inactive form of phytochrome having a maximum absorption in the red region	It is an active form of phytochrome with maximum absorption in region of far-red.
It absorbs red light, then gets converted into Prf form	It absorbs Pfr form of far-red light and then gets changed into Pr form
Pr form is present diffused in the cytoplasm	Pfr form is present in association with the dense cytoplasmic bodies

The phytochrome method also is used by plants to change the growth by season. The biological reaction to the time and length of light and darkness cycles is photoperiodism. Since, in the early days, all phytochrome molecules in a leaf are rich in red light, but in far-root light, they become active Pfr and remain in this state until sunset. Since Pfr returns to Pr during the darkness, no Pfr will remain at the rising of the sun if the night is long (winter) (summer). The amount of Pfr is present that stimulates flowering, winter bud setting and seasonal vegetative development.
Note: 1)Phytochrome: a pigment class which controls the majority of photomorphogenic response in higher plants.
2)Chromophore: a group of atoms of a molecule that is responsible for the electronic transition for a given spectral band.
3)Photoperiods: formation, development and other reactions by day and/or night for plants and animals.