A gibberellin insensitive mutant of Arabidopsis thaliana

A dwarf mutant of Arabidopsis thaliana (L.) Heynh. was found to be less sensitive to applied gibberellins than the wild type, and this character was controlled by one partially-dominant gene (denoted Gai) located on chromosome 1. This mutant resembled gibberellin-deficient mutants since not only stem growth, but also apical dominanace and seed germination were reduced. However, in contrast to the latter mutants, gibberellin does not reverse these effects in the Gai mutant. The insensitivity of the mutant could be quantified in much more detail in the recombinant of this mutation with the GA deficient mutant ga-1/ga-1 . Endogenous gibberellins of the Gai mutant did not differ from the wild type either in quantity or composition. The data suggest that the gene controls a step involved in gibberellin action.     

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.