ISSN 10214437, Russian Journal of Plant Physiology, 2012, Vol. 59, No. 4, pp. 479–490. © Pleiades Publishing, Ltd., 2012.
Seventy five years ago the term “florigen” was
coined by Chailakhyan in 1936  to explain photope
riodic regulation of plant flowering; his and other evi
dence [1, 2], indicated leaftoshoot apex transport of
some form of flowering signal(s). Forty years later in
1976 Chailakhyan  wrote that “the nature of flow
ering hormones is unclear”. He did comment on the
“high activity and ability of gibberellins to induce and
stimulate flowering in plants”, but then concluded
that they were “not the florigen” but part of the flori
gen complex and principally responsible for the
growth of flower stems; a second group of hypothetical
substances, he termed anthesins, were responsible for
There is no doubt that applied gibberellins (GAs)
are highly effective regulators of stem elongation and
flowering in plants (see reviews by Zeevaart , Pharis
and King ). Both responses occur almost simulta
neously and could be a part of common GA regula
tion. Nevertheless, in a number of dicotyledonous
The article is published in the original.
plants, treatments to reduce or increase GA levels
showed flowering responses where GA failed to
increase elongation and, conversely, a GAregulated
increase in elongation but with no flowering (reviewed
in ). Such evidence apparently played a part in
Chailakhyan’s reticence to call GA a florigen.
Subsequently, Zeevaart  endorsed claims that
the protein FT is a florigen transported from the leaf to
the shoot apex of longday (LD) and shortday (SD)
plants (see Corbesier et al. , Tamaki et al. , and
reviews by Turck et al.  and Turnbull ). His pref
erence was to “restrict the term florigen to
transmissible signals”. Nevertheless, in the same para
graph Zeevaart did not rule out GA as a florigen in
temperate grasses, including
Evidence is reviewed here for a florigenic role for
GA in both mono and dicotyledonous plant species
(see also ). For identifying floral stimuli (flori
gens), five simple, logical rules apply:
(i) The factor should replace the photoperiodic
requirement for flowering.
(ii) The factor should be increased in the leaf at the
time of floral induction.
(iii) The factor should be transported to and
increased at the shoot apex at floral evocation.
Mobile Signals in Day LengthRegulated Flowering:
Gibberellins, Flowering Locus T, and Sucrose
R. W. King
CSIRO Plant Industry, GPO Box 1600, Canberra City, ACT 2601, Australia;
Received August 5, 2011
—Despite low activity for stem growth, the gibberellins GA
act as longday (LD) florigens
L. This claim is based on extensive evidence covering GA synthesis in LD in the
induced leaf and their transport to the shoot apex where they act in a dosedependent manner. GAs also act
as a LD florigen in association with cold vernalization of
In contrast, highly bioactive GA
are important florigens in
(L.) Heynh. This species contrast reflects differ
ences in GA deactivation, which is unimportant for Arabidopsis but dominant in
It is unclear
if GAs participate in flowering responses of shortday (SD) species since it is LD, which upregulate enzymes
for GA biosynthesis. Sugars (sucrose) may also act directly as a florigen and, specifically, with increase in pho
tosynthesis as in LD or when light intensity is increased in SD. In addition, in LD sucrose can indirectly cause
flowering by upregulating
expression, the FT protein acting as a further leaftoapex transported florigen.
Thus, there are not only multiple florigens but there can be complex interactions between the signaling path
ways controlling production of these various florigens.
Arabidopsis, Lolium temulentum
, flowering, FT, gibberellin, GA synthesis and deactivation, long
day plants, multiple florigens, sucrose.
: FR—farred light, FT—Flowering Locus T,
GA—gibberellin, LD—long day, SD—short day, TNE—trinex