Photoperiodism II Role of Phytochromes in Flowering II Red Light and Far-red light effect

We know that plants are living, and can respond to sunlight. Photoperiod is the period of time each day during which an organism receives illumination; day length.
The ability of plants to measure the length of photoperiods is known as Photoperiodism
Flowering, seed germination, asexual reproduction, and seed dormancy in plants are triggered by the photoperiod of a certain length
This specific photoperiod is called Critical day length
Length of Critical Period VARIES between species & Plants, thus we can classify plants based on their photoperiodism as Long Day plants that are like to work for long day.
Then there are Short day plants, that like to wrap up the work quickly and take a long break.
Then there are Day neutral plants who are unaffected by the photoperiodism
As we know Long Day plants that are like to work for long day, So when the Day time is more than the night time, we see flowering. But, since they do not like big rest time , there is no flowering if night time is more. However, if the long night time has a short light time in between it means they got some productive time during the rest period, and so they can flower. This interruption of night with a flash of light is called Night break
Short day plants want to wrap up their work quickly and take rest so when the day is short and they have a big night time they flower, But, when the day is long and the night is short, they do not like it, and so they do not give flowers.
Also if their rest time is disturbed by light, they do not like it either, and no flowering happens
Plants measure the Photoperiod using Phytochromes in leaves, which acts as photoreceptor of photoperiodic stimulus
Phytochromes are Dimers formed by two monomers. They are present in two forms which are photo-reversible. Phytochromes are naturally synthesized in the Pr form. When the Pr form is exposed to red light, it is converted to the Pfr form. This change can be reversed by the exposure to far red light.
Thus, in response to the photoperiod, the leaves are capable of sending signals that regulate the flowering and seed germination.
Exposure of plants to red and far red light leads to the photo-reversible of phytochrome Pr and Pfr. The presence of Pr or Pfr forms determines the flowering in long day and short day plants
When long day plants receive a flash of red light, they produce flowers i.e in Pfr form. However, when they are exposed to far red light, flowering is prevented.
The exact opposite happens in case of short day plants.
Red light i.e. the Pfr form prevents flowering in short day plants, whereas far red light or the Pr form promotes flowering
A trick to remember this will be by remembering the company Leaf Research Foundation Pvt Ltd.
This means Long day plant in presence of Red Light will give flowers due to the Pfr form. If we see this arrangement from bottom, we get Pfr form which reminds us that this change is happening due to the Pfr form of the Phytochrome. Also we will remember that red light gives the Pfr form, and this induces flowering in Long day plants. Thus, we remember that far red light will prevent flowering due to the Pr form. Also in case of short day plants the effect will be exactly opposite to that of Long day plants.
To summarize it, long day plants love to work during the day for long hours, and hate long nights. However, if the long night is with a short productive break they love that too
Short day plants are very lazy, they want to rest all the time with no disturbance
To remember how phytochromes regulate flowering in plants we have the Leaf Research Foundation Pvt limited to take care of it.
Also Blue light can induce opening of stomata and leaflets and flowering in some long day plants.

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