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 a nd fwa); the hy2 and hy3, late-flowering double mutants and the hy2,hy 3, late-flowering triple mutants. The hy mutants flower with fewer ros ette leaves than the Landsberg erecta wild type under both long day an d short day conditions and express this effect to a different degree i n all late-flowering mutant backgrounds and under both daylengths, wit h 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 ge nes on the various parameters that describe the transition to flowerin g in Arabidopsis is discussed.