Classification Of A Brassica Napus Dwarf Mutant And Preliminary Investigation For The Mechanism Of Dwarfing

A Brassica napus dwarf line "DDF-1" has been derived from a combination of a elite high line and a dwarf mutant 'NDF-1' which was obtained from a doubled haploid inbred line' 3529' induced by fast neutron and diethyl sulfate (DES) . Characterized as logging resistance and relatively high harvest index, the "DDF-1" line, with reduced plant height of about one third of its wild ancestor, is a very important germ resources for oilseed rape breeding aimed to mordern farming.Effects of exogenous gibberellin (GA₃), auxin (IAA) and brassinosteroids (BRs) application on early seedling growth of a Brassica napus dwarf mutant, namely "DDF-1", was studied. Histological analysis showed that in contrast to wild type the DDF-1 hypocotyls cell length. ELISA (enzyme-linked immune sorbent assay) was used to determine the contents of endogenous hormones. SDS-PAGE was used to find a protein concatenated with the hypocotyl elongation. Through the above experiment, we had made sure its dwarf type and initially concluded its dwarfed reason.The results showed that proper exogenous GA₃ (7mg/L) applied could partially rescued the hypocotyl elongation of the dwarf, but no significant differences made by IAA and BRs at any levels of application. Furthermore, no interaction effects of GA₃, IAA and BR on the elongation of the seedling hypocotyls were detected by orthogonal test of these hormones. Vertical section of hypocotyls of the dwarf indicated a reduction for the cell length in comparison with the wild type, which may lead to the shorter hypocotyl of the mutant. GA₃ was active inducing the DDF-1 hypocotyl elongation in light, but not in the dark. These results show that light might increase sensitivity of seed to exogenously applied GA₃. Therefore we thought DDF-1 is the gibberellin mutant.Through the result of gibberellin concentration gradient, the "DDF-1" hypocotyle elongation needs the GA₃ concentration 1000 times than the wild type. But under the GA₃ saturated concentration, the hypocotyl elongation of the dwarf is shorter than wild type and each kind of concentration gibberellin all cannot make the "DDF-1" hypocotyl to restore to the length of wild type. Early seedling's endogenous GA₃ and ABA content, determined by ELISA, showed higher in the dwarf than in the wild type and the adult plant's endogene gibberellin content still was higher in the dwarf than in the wild type. So we think the dwarf mutant "DDF-1" was GA insensitive.The hypothesis, suggesting that the dwarf mutant was GA insensitive and controlled by mutated gene(s) in gibberellins signal transduction pathway, was discussed. It may be the mutate gene coding the F-box protein GID1 that is GA binding protein. The GID1 was expressed in the low level or had the protein conformational changes. So the GID1 cannot bind the free GA and also cannot initiate a GA-dependent interaction with SLR1, leading to SLR1 degradation. GA transcriptional responses cannot be opened, the mutation showed dwarfing.SDS-PAGE was used to find the hypocotyl protein concatenated with the hypocotyl elongation. The results showed that protein content concatenated with the hypocotyl elongation. The hypothesis suggested that the protein might be the F-box protein GID1.