Photoperiodism

PHOTOPERIODISM (Term by Garner and Allard)

The response of plants to changes in the relative lengths of day and night is called photoperiodism.

Photoperiod

 The relative lengths of dark and light periods in a day vary from place to place and from season to season. The length of light period is called photoperiod. At equators, day length is of 12 hours duration throughout the year. Plants flower only when exposed more or less than a certain light period called critical photoperiod.

Types of plants according to photoperiodic requirements for flowering :

For SDP  while for LDP is critical for flowering

Photoperiodic stimulus is perceived by leaf.

When proper photoperiod is perceived a flowering hormone called florigen is synthesized in leaf and is transported to bud through phloem, where flowering occurs.

Florigen is a hypothetical hormone and is chemically similar to gibberellins.