IN VIVO GIBBERELLIN A9 METABOLISM BY AZOSPIRILLUM SP. IN dy DWARF RICE MUTANT SEEDLINGS

Azospirillum sp. are bacteria beneficial to inoculated plants, and the effect is partially attributed to gibberel lin production. Deutero-labelled GA9 was fed to dy mutant rice-dwarf seedlings inoculated with A. lipoferum or A. brasilense and/or treated with Prohexadione-Ca, an inhibitor of late steps in gibberellin biosynthesis. According to the shoot growth response, the mutant showed the ability to perform 3?-hydroxylation of the d2GA9 fed. This ability was partially blocked by Prohexadione-Ca, suggesting that GA9 may have some activity per se . After the feeding was done along with Azospirillum sp. inoculation, the bacteria performed 3?-hydroxylation as shown by shoot growth promotion and corroborated by GC-MS detection of d2GA3. The growth promotion was blocked by Prohexadione-Ca but in a lower extent as compared with non-inoculated controls, suggesting that the inhibitor worked on the 3?hydroxylation performed on the substrate fed but on the microorganism capacity to produce “active” gibberellins. Keywods: Azospirillum, gibberellins, rice