The effect of daylength on the transition to flowering in phytochrome‐deficient, late‐flowering and double mutants of Arabidopsis thaliana

The effect of daylength on flowering was investigated in the following mutants of Arabidopsis thaliana: phytochrome B deficient (hy3=phyB); phytochrome chromophore deficient (hy2); late-flowering (co, gi. fca and fwa); the hy2 and hy3, late-flowering double mutants and the hy2, hy3, late-flowering triple mutants. The hy mutants flower with fewer rosette leaves than the Landsberg erecta wild type under both long day and short day conditions and express this effect to a different degree in all late-flowering mutant backgrounds and under both daylengths, with the exception of fca under short days. The number of cauline leaves and days to flowering is less affected by the hy genotype. The hy2, hy3 double mutants flower with even fewer rosette leaves than the hy2 and hy3 monogenic mutants, suggesting an inhibitory role for phytochrome B and other stable phytochromes on flowering. The complex interaction between phytochrome, daylength and the effect of the late-flowering genes on the various parameters that describe the transition to flowering in Arabidopsis is discussed.