Florigen

Florigen or Flowering hormone are the terms used for the hypothesized hormone-like molecules that control and/or trigger flowering in plants. It has recently been shown to be the protein of the FT gene.

History
Florigen was first described by Russian plant physiologist Mikhail Chailakhyan in 1937, who demonstrated that floral induction can be transmitted through a graft from an induced plant to one that has not been induced to flower.

Anton Lang showed that several long-day plants and biennials could be made to flower by treatment with gibberellin, when grown under a noninducing photoperiod. This led Chailakhyan to modify his florigen hypothesis to postulate two classes of flowering hormones: Chailakhyan postulated that during noninducing photoperiods, long-day plants produce anthesin, but no gibberellin while short-day plants produce gibberellin, but no anthesin. However, these findings did not account for the fact that short-day plants grown under noninducing conditions (thus producing gibberellin) will not cause flowering of grafted long-day plants that are also under noninductive conditions (thus producing anthesin). The flowering hormone has eluded scientists for over sixty years, as the flowering response has been found to be increasingly complex. A possible hypothesis is that florigen does not exist; rather, a particular ratio of other hormones must be achieved for the plant to flower.
 * Gibberellins
 * Anthesin

However, recent experiments suggest that florigen does exist. Its existence is substantiated by experiments that indicate that the substance that triggers blooming is produced or activated in the leaves of the plant, and must be given time to pass out of the leaves before the plant can flower.

The signal has been shown to be the messanger RNA of a gene called FT. This RNA travels from leaves to the growing tip in the phloem, where the FT protein interacts with a transcription factor, called FD.

[RNA has recently been proven to be the wrong molecule. The currently accepted one is that the protein itself acts as the signal.]

Recent Experiments
Recent work has implicated two genes, FT and CO, as possible components of the florigen signal. A review of recent (2006) progress in the quest for florigen can be found at .(| Oxford Journals).