Plants have to coordinate the production of flowers to coincide with the best reproductive opportunity . There are many environmental cues that affect flowering however the photoperiod isthe most reliable indicator on time of the year.
The photoperiod is the period of day light in relation to dark. In northernly and southern regions, this photoperiod is a reliable indication of the time of year and therefore one of the most reliable indicators of the seasonal changes.
Short and Long day Plants:
Short day plants (SDP) typically flower in the spring or autumn when the length of day is short.
Long day plants (LDP) typically flower during the summer months of longer photoperiod.
Critical Night Length:
Experiments have shown that the important factor determining flowering is the length of night rather than the length of day.
Therefore, SDP have a critical long night and LDP will have a critical short night.
The receptor of photoperiod is located within the lead but the cellular location of the receptor remains unclear. The chemical nature of the receptor is the molecule Phytochrome and phytochrome can be converted from one form to another by different types of light