Abstract: Dwarf and semi-dwarf mutants are the valuable materials for investigating plant gene function and developing new crop variety with high seed yield and lodging resistance. In the present study, the developing plants of dwarf (df) and semi-dwarf (sdf) mutants and their wild-types (WTs) in different growth stages were treated with exogenous gibberellin A₃ (GA₃) in order to analyze responses of plant growth rate, plant height, and vertical cell length from the main stem to exogenous GA₃ (40 mg L^-1), as well as the endogenous GA₃₊₁ level differences between two types of mutants and their WTs. The results indicated that the responses of plant growth of the sdf and df mutants to the exogenous GA₃ were significantly different, demonstrating that GA₃ treatment led to the average rate (2.76 cm d^-1) of plant growth of the sdf mutant in different measuring-time intervals to be significantly higher than that (1.10 cm d^-1) of water treatment (control); but the average rate of plant growth (0.92 cm d^-1) of GA₃-treated df mutant was slightly higher than that (0.56 cm d^-1) of control, and moreover df mutant plants in the prophase of entire growth period only had a little response to exogenous GA₃. In addition, after GA₃ treatment the average plant height, internode length, and vertical cell length of the internode on the main stem of sdf mutant were much higher than those of df mutant, verifying the exogenous GA₃ treatment could recover plant height phenotype of WT-sd in sdf mutant, while not recover that of WT-d in df mutant. The node number on the main stem of two types of mutants was almost no response to GA₃. Based on above results we think that sdf is a GA₃-sensitive soybean mutant, and df is a GA₃-insensitive soybean mutant. Furthermore it was found that the endogenous GA₁₊₃ levels in sdf and df mutant plants were remarkably lower than that in their WT plants, which may be the physiological cause of dwarfism for sdf and df mutants.

Key words: Glycine max (L.), Dwarf/semi-dwarf mutant, Gibberellin, Plant growth, Plant height trait