Control of Flowering in Arabidopsis thaliana by Light, Vernalisation and Gibberellins

Abstract

The late flowering mutants of the Landsberg erecta race of Arabidopsis thaliana (L.) Heynh. were responsive to both vernalisation treatment and the ratio of red: far-red light (660 : 730 nm) with regard to time to flower and the numbers of leaves formed prior to flowering. The most vernalisation-sensitive mutants, fca, fve, fy and fpa, were also the most sensitive with regard to changes in the red:far-red light ratio. These responsive mutants flowered up to 40% earlier under lighting that included a greater proportion of far-red (730 nm) light from incandescent lamps compared with plants under light at the same photon flux density (PFD) with a greater proportion of energy from fluorescent lamps. Conversely, the mutants that were only slightly responsive to vernalisation (co, gi and fe) were also least responsive to changes in red:far-red ratio. The correlation between responsiveness to vernalisation and responsiveness to changes in red: far-red for the 11 mutants and Landsberg was highly significant (r2 = 0.88). Time to flower and leaf number at flowering were also markedly affected by changes in PFD in the vernalisation-sensitive mutants. Halving the PFD approximately doubled time-to-flower and leaf number of fca, the most responsive of the late flowering mutants, whereas there were only slight changes in the flowering responses of the parent Landsberg. Thus, these single point late flowering mutants are responsive not only to vernalisation but also to changes in light quality and PFD. These responses imply that both daylength perception and photosynthesis have been affected by the mutations. Gibberellins (GAS) induced earlier flowering not only in the late flowering mutant fca, but also in Landsberg, when that race was grown in short days. Dosages of 5 μg plant-1 of GA3, GA5 and GA9 were equaIly effective in promoting flowering of 15-day-old fca plants with subsequent flowering 9-13 days earlier with 4-6 fewer leaves. Photoperiodic sensitivity to a single long day 15 days after sowing showed Landsberg flowering 6 days earlier and with 1.4 fewer leaves than plants continuously in short days.