by Ramneet Kaur


Photoperiodism is the effect of light on flowering.

  • Garner & Allard 1st reported the effect of light on flowering in Maryland Mammoth (variety of tobacco) & Glycine max.
  • On the basis of photoperiodic requirements, plants are divided into 3 types:

  • Short day plants: in these plants, the dark period is very important for flowering. The dark period should exceed a critical length. Light has no effect on flowering. E.g., rice, sugarcane, potato, tobacco, soybean, Chrysanthemum.
  • Long day plants: in these plants, the light period is very important for flowering. The light period should exceed a critical length. Darkness has an inhibitory effect on flowering. E.g., wheat, oat, spinach, radish, barley, lettuce.
  • Day-neutral plants: these plants blossom throughout the year. Length of light or dark period has no effect. E.g., tomato, cucumber, sunflower, cotton, maize, pepper.

  •  Leaves receive the photoperiodic stimulus. The minimum number of appropriate photoperiods required for induction is 1 to 25.
  • Effect of light on flowering is due to the presence of a photoreceptive pigment called Phytochrome. Discovered by Hedrick & Borthwick.

Phytochrome occurs in 2 forms that are inter-convertible. PR & PFR form.


  • PR form absorbs red light (during the day) & changes into PFR,
  • While the PFR absorbs far-red light (during night) & changes back to PR.
  • PFR is the physiologically active form.
  • In short day plant, Pform causes flowering.
  • In long day plant, PFR form causes flowering.

  • A flowering hormone called Florigen (hypothetical) is produced in the leaves that are transferred to the shoot apices which causes flowering.


You may also like

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Lets make Biology simple

This website uses cookies to improve your experience. We'll assume you're ok with this, but you can opt-out if you wish. Accept Read More


Join Our Newsletter Today!

Stay updated with all latest MCQs, Topic Summary, Mnemonics, Videos, tips & tricks for Biology.

Send this to a friend

Skip to toolbar