Florigen

Article By:

Ayre, Brian G. Department of Biological Sciences, University of North Texas, Denton, Texas.

Last reviewed:January 2020

DOI:https://doi.org/10.1036/1097-8542.900131

A hormone-like protein that controls when a plant will flower in response to the changes in day length associated with the different seasons. Florigen is produced in leaves, where changes in day length are perceived, and migrates through the phloem vascular system to the buds, where flowers develop. Although the physiological impact of florigen has been known since the early part of the twentieth century, extensive efforts to identify the active compound led to numerous false leads and were ultimately unsuccessful. This garnered florigen some notoriety, and it became the “Holy Grail” of plant biology until 2007, when a 175-amino-acid protein, encoded by the FLOWERING LOCUS T gene in Arabidopsis thaliana, was identified as the active compound (or at least as a predominant component of a mixture of compounds). As a protein with a molecular weight of 19.8 kilodaltons (kDa), florigen differs from canonical plant hormones by virtue of its large size, chemical composition, and mode of transport, which is entirely within the shared cytoplasm of plant cells (that is, the symplasm) and does not have extracellular steps. See also: Plant; Plant hormones; Plant organs; Plant physiology

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