It is through "the evolution of both internal and external control systems that enables plants to precisely regulate flowering so that it occurs at the optimal time for reproductive success.
Although it was originally thought that the accumulation of photosynthetic products controlled the flowering of plants, two men by the names of Wightman Garner and Henry Allard proved it was not.
The light essentially stimulates the transmission of a floral stimulus (florigen) to the shoot apex when the correct amount of day-length is perceived.
[6] The mechanism may be broken down into three stages: photoperiod-regulated initiation, signal translocation via the phloem, and induction of flowering at the shoot apical meristem.
In Arabidopsis thaliana, the signal is initiated by the production of messenger RNA (mRNA) coding a transcription factor called CONSTANS (CO).
CO mRNA is produced approximately 12 hours after dawn, a cycle regulated by the plant's circadian rhythms, and is then translated into CO protein.
[10] By this mechanism, CO protein may only reach levels capable of promoting FT transcription when exposed to long days.
[6] The FT protein resulting from the short period of CO transcription factor activity is then transported via the phloem to the shoot apical meristem.
[3][11][4] Florigen is a systemically mobile signal that is synthesized in leaves and the transported via the phloem to the shoot apical meristem (SAM) where it initiates flowering.
Upon this conclusion, it became important to understand the process by which the FT protein causes floral transition once it reaches the SAM.
[17] Anton Lang showed that several long-day plants and biennials could be made to flower by treatment with gibberellin, even when grown under a non-flower-inducing (or non-inducing) photoperiod.
[21] First report of FT mRNA being the signal transducer that moves from leaf to shoot apex came from the publication in Science Magazine.
However, in 2007 other group of scientists made a breakthrough saying that it is not the mRNA, but the FT Protein that is transmitted from leaves to shoot possibly acting as "Florigen".
Light activates photo-receptors[7] and triggers signal cascades in plant cells of apical or lateral meristems.