Azospirillum brasilense and Azospirillum lipoferum Hydrolyze Conjugates of GA(20) and Metabolize the Resultant Aglycones to GA(1) in Seedlings of Rice Dwarf Mutants

Azospirillum species are plant growth-promotive bacteria whose beneficial effects have been postulated to be partially due to production of phytohormones, including gibberellins (GAs). In this work, Azospirillum brasilense strain Cd and Azospirillum lipoferum strain USA 5b promoted sheath elongation growth of two single gene GA-deficient dwarf rice (Oryza sativa) mutants, dy and dx, when the inoculated seedlings were supplied with [17,17-(2)H(2)]GA(20)-glucosyl ester or [17,17- (2)H(2)]GA(20)-glucosyl ether. Results of capillary gas chromatography-mass spectrometry analysis show that this growth was due primarily to release of the aglycone [17,17-(2)H(2)]GA(20) and its subsequent 3β-hydroxylation to [17,17-(2)H(2)]GA(1) by the microorganism for the dy mutant, and by both the rice plant and microorganism for the dx mutant.