The plant-growth-promoting rhizobacteria Bacillus pumilus and Bacillus licheniformis produce high amounts of physiologically active gibberellins

The plant-growth-promoting rhizobacteria (PGPR), Bacillus pumilus and Bacil lus licheniformis, isolated from the rhizosphere of alder (Alnus glutinosa [L,] Gaertn,) have a strong growth-promoting activity, Bioassay data showed that the dwarf phenotype induced in alder seedlings by paclobutrazol (an i nhibitor of gibberellin [GA] biosynthesis) was effectively reversed by appl ications of extracts from media incubated with both bacteria and also by ex ogenous GA(3). Full-scan gas chromatography-mass spectrometry analyses on e xtracts of these media showed the presence of GA(1), GA(3), GA(4) and GA(20 ), in addition to the isomers 3-epi-GA(1) and iso-GA(3). Isotope dilution a nalysis indicated that epi-GA(1) was an artefact. Likewise, iso-GA(3) is al so probably an artifact spontaneously formed during extraction and/or analy sis. In both culture media, GA(3) was present in higher concentrations (130 -150 ng ml(-1)) than GA(3) (50-60 ng ml(-1)), GA(4) (8-12 ng ml(-1)) and GA (20) (2-3 ng ml(-1)). The data indicated that culture of both bacteria accu mulate bioactive G(19)-gibberellins in relative high amounts and that these GAs appear to be physiologically active in the host plant, The evidence su ggests that the promotion of stem elongation induced by the PGPR could be m ediated by bacterial GAs.