DWARF MUTANTS OF BRASSICA - RESPONSES TO APPLIED GIBBERELLINS AND GIBBERELLIN CONTENT

Eight rapid-cycling Brassica genotypes differing in height were treated with gibberellins (GAs) by syringe application to the shoot tip. The height of two genotypes of Brassica napus, Bn5-2 and Bn5-8, and B. rapa mutants, dwarf 1 (dwf1) and dwarf 2 (dwf2), was unaffected by exogenous GA3 at dosages up to 0.1-mu-g/plant, a level which increased shoot elongation of normal genotypes. Thus, these dwarf mutants are "GA-insensitive." In contrast to the B. napus dwarfs, two B. rapa mutants, rosette (ros), and dormant (dor), elongated following GA3 application. The dwarf ros was most sensitive, responding to applications as low as 1 ng GA3/plant. Furthermore, ros also responded to GA1 and some of its precursors with decreasing efficacy: GA3 > ent-kaurenoic acid greater-than-or-equal-to GA1 > GA20 greater-than-or-equal-to GA19 = GA44 greater-than-or-equal-to GA53. Endogenous GAs were measured by gas chromatography-selected ion monitoring using [2-H2]GA internal standards for calibration, from shoots of the GA-insensitive genotypes Bn5-2, Bn5-8 which contained the B. napus mutant dwarf 1, and from a normal genotype Bn5-1. Concentrations of GA1 and GA20 averaged 3.2- and 4.6-fold higher, respectively, and GA19 levels also tended to be higher in the dwarfs than in the normal genotype.