Far-red light and long photoperiods promote flowering in Arabidopsis.
We report here that when 30-day-old vegetative plants were induced wit
h a continuous light treatment enriched in far-red light, flowers deve
loped directly from previously initiated primordia. Specifically, plan
ts induced with our continuous incandescent-enriched (CI) treatment pr
oduced an average of two primary-axis nodes with a leaf/flower phenoty
pe, indicating that approximately two leaf/paraclade primordia per pla
nt produced an individual flower from tissue that typically would diff
erentiate into a paraclade (secondary inflorescence). Assays for APETA
LA1::beta-glucuronidase activity during the CI photoinduction treatmen
t indicated that the floral meristem identity gene APETALA1 was transc
riptionally activated in primordia with a leaf/paraclade bias and in p
rimordia committed to leaf/paraclade development. APETALA1 ::P-glucuro
nidase activity levels were initially highest in young primordia but w
ere not correlated strictly with primordium fate. These results indica
te that primordium fate can be modified after primordium initiation an
d that developing primordia respond quantitatively to floral induction
signals.