Gibberellin Production by Azospirillum lipoferum Cultured in Chemically-Defined Medium as Affected by Oxygen Availability and Water Status

PICCOLI; MASCIARELLI O; BOTTINI R

SYMBIOSIS

SPRINGER

Año: 1999 vol. 27 p. 135 - 146

0334-5114

Azospirillum growing in plant roots will experience varying water potentials and O2 concentrations. Here we have investigated the effect of varying water potential or O2 concentration on growth and gibberellin A3 (GA3) production of Azospirillum cultures. Azospirillum lipoferum strain USA 5b was grown in Nitrogen-Free biotin medium (NFb) with malic acid (5 g l-1) and NH4Cl (1.25 g l-1) as the C and N sources. Different water potentials (w) in the media were made up by varying the NH4Cl concentration, or with the addition of polyethylene glycol (PEG 8000). Different O2 concentrations in the medium were obtained by varying the volumes of medium in 135 ml flasks with or without gas exchange. Gibberellin identity and quantity was assessed from the bacterial cultures by capillary gas chromatography-selected ion monitoring with [2H2]gibberellins as internal standards. Bacterial growth and viability was reduced by increasing the NH4Cl concentration, increasing the PEG concentration, or restricting gas exchange. The total GA3 (the main gibberellin identified from Azospirillum spp.) produced by each culture was reduced severely at high NH4Cl or with restricted gas exchange. With PEG however, the total GA3 was reduced by only 50% at the highest concentration (w = -1.21 MPa) despite a 90% reduction in cell numbers, reflecting an increase in GA3 produced per cell with increasing PEG concentration. This result helps to explain the positive effects of rhizospheric and endophytic Azospirillum spp. in alleviating the effects of water stress in infected plants through gibberellin production