Here is some good reading on far red and red to promote flowering. Just found this. It's long sorry..


Photoinduction of floral determination and flower initiation

We have shown that the Nossen ecotype of Arabidopsis, like
the Columbia ecotype (Corbesier et al., 1996), can be induced
to flowering by one long day provided the red-to-far-red ratio
is sufficiently low. Under red-enriched (R) conditions, floral
determination required a total of 20-24 hours of continuous R
light, which is more than one 16-hour long-day. In contrast,
adding 4 hours of far-red-enriched (FR) light to the end of an
8-hour day of red-enriched light was sufficient for floral determination.
The greater effectiveness of the FR treatment
compared to the R treatment occurred despite a considerably
lower total irradiance, consistent with previous reports that far red
light is an effective promoter of flowering in Arabidopsis
(MartÃ*nez-Zapater and Somerville, 1990; Goto et al., 1991;
Bagnall, 1993; Lee and Amasino, 1995).

Control plants induced with continuous FR-light had fewer
leaves than plants that received the briefest FR treatment, of
only 4 hours. Similarly, floral determination occurred sooner
in control plants that were moved permanently to continuous
FR conditions compared to those placed permanently in continuous
R conditions. These differences can be explained in
one of two ways. One possibility is that there is a conversion
of the youngest existing primordia into flower primordia when
floral induction signals are sufficiently strong. This would
suggest that the fate of the emerging primordia or anlagen is
plastic until a certain stage, and that even primordia that have
already adopted a bias towards leaf/paraclade fate will assume
a floral fate if the inductive signal is potent enough (e.g., in the
continuous FR treatment). This first explanation is consistent
with evidence that in many plants, including Arabidopsis, primordium
fate is specified progressively during development
(Battey and Lyndon, 1990; Bradley, et al., 1996; Hempel,
1996). Alternatively, the production of a small number of
leaves may occur after the start of relatively weak inductive
conditions (e.g., in the 4 hour FR treatment and in the continuous
R treatment). Expression of floral regulatory genes during photoinduction

The higher effectiveness of the FR treatment, versus the R
treatment, in promoting a rapid switch from the production of
leaf/paraclade to flower primordia was not paralleled by pronounced
differences in AGL8::GUS and LFY::GUS activity
profiles. Accordingly, while the increase in LFY::GUS and
AGL8::GUS activity was concurrent with floral determination
in the FR treatment, the initial increase in LFY::GUS and
AGL8::GUS activity in the R treatment preceded floral determination
by 12 hours. A subsequent decrease in LFY::GUS
activity in the R treatment was clearly evident after 12 hours
of continuous photoinduction, suggesting a potential role for
circadian rhythms in the regulation of LFY.

The unexpected lack of correlation between specific levels
of LFY::GUS and AGL8::GUS activity and floral determination
may indicate that while FR and R treatments are similarly
effective in inducing LFY and AGL8, the R treatment was less
effective in promoting the competence to respond to these
floral regulators. Recent analyses have demonstrated that in
addition to absolute LFY levels, other â??competenceâ?? factors
modulate responses to LFY in the apex (Weigel and Nilsson,
1995; Blázquez et al., 1997). In this context, the slight decrease
in LFY::GUS activity after 12 hours of the R, but not the FR
treatment, suggests that one aspect of competence is the ability
to maintain levels of LFY expression after an early acute
response.

Additionally, since we assayed for determination at the
whole-plant level, it is possible that the first changes which
induced â??determinationâ?? in our experiments occurred in the
leaves (Zeevaart, 1958; Chailakhyan, 1968). If this is the case,
the level of LFY expressed in a shoot apex, even shortly after
determination has occurred, need not be sufficient for the production
of flowers. The low levels of LFY::GUS evident in the
apex around the time of determination, in our experiments,
may simply indicate that although the leaves were determined
to send signals sufficient to induce flowering (and floral
regulator function), the signals had not yet arrived in full. This
explanation fits with experiments on Lolium temulentum and
Ipomoea nil which indicate that determining changes in the
leaves precede those in the shoot apex by a few hours (Larkin
et al., 1990; McDaniel et al., 1991).

Diffuse patterns of LFY::GUS and AGL8::GUS were seen
during the first 2 days of photoinduction, and early AP1::GUS
expression was also somewhat diffuse and not strictly localized
to flower primordia. Likewise, the expression of LFY, AGL8
and AP1 RNAs was relatively diffuse during the first 2 days of
photoinduction, and qualitatively similar to that of the corresponding
reporter constructs. These initially diffuse expression
patterns might reflect that upstream regulators of flowermeristem-
identity genes are not strictly localized to emerging
floral primordia, but that once floral induction has taken place,
subsequent interactions among flower-meristem-identity genes
are required to sharpen their expression patterns, similar to that
observed in other developing primordia such as the Drosophila
wing (Rulifson et al., 1996).

In these experiments, AP1::GUS activity was a sensitive
marker for floral determination in both FR and R conditions.
Although AP1::GUS was expressed when flower primordia
were still morphologically indistinguishable from leaf
primordia, we detected AP1::GUS activity only after floral
determination. Thus, our results concur with a recent report
indicating that LFY expression precedes AP1 expression when
flowering is induced photoperiodically, as well as when it is
induced by ectopic expression of the flower-promoting gene
CONSTANS (Simon et al., 1996).

Quantitative aspects of floral induction

The photoinduction of flowering involves complex interactions
between the leaves and the shoot apex. Leaves perceive both
photoperiod and light quality (Knott, 1934; Bernier et al.,
1993) and send signals to the shoot apex, which is the site of
flower production. Floral induction signals from the leaves and
other regions of the plant (McDaniel et al., 1992; Kinet et al.,
1993), are integrated at the shoot apex, and in sufficient
quantity, they induce the initiation of flowers and the
expression of flowering genes.
The specific molecular processes which commit an Arabidopsis
plant to flower are yet to be defined, and our experiments
do not resolve the question of whether floral determination
is regulated in the leaves or at the shoot apex. However,
our results show that plants that are developing a flowering
bias, as indicated by transient increases in LFY::GUS and
AGL8::GUS expression, can remain vegetative if returned to
non-inductive conditions. This indicates that flower specification
is a quantitative process both with respect to the perception
of flower-promoting light signals in leaves and to the
activity of floral regulatory genes at the shoot apex (McDaniel
et al., 1991; Bowman et al., 1993; Schultz and Haughn, 1993;
Bradley et al., 1996; Blázquez et al., 1997).