Protective Strategies Induced by Azotobacter sp. Strain and its Role after Exposure to H2O2 in Improving Hibiscus sabdarriffa Performance

THE EFFECT of hydrogen peroxide (H2O2) solutions, applied to pure cultures of Azotobacter at concentrations ( 0.0, 0.05, 0.1 and 1%), was determined by measuring survival, protein content, antioxidant enzymes, H2O2 content and malondialdehyde content after 15 and 30 min. The impact of the treated bacteria to affect seed vigour of Hibiscus sabdarriffa was then evaluated. Survival of Azotobacter cells was not affected significantly at H2O2 concentrations of 0.05 % and 0.1 % after 15 min (11 % and 34 % reduction, respectively) compared to the control. With 30 min exposure, the protein content was reduced 2 fold compared to 15 min exposure time. However, for superoxide dismutase (SOD), ascorbat peroxidase (APX) and catalase (CAT), no significant differences were observed at low concentrations of H2O2, but only at the highest concentration (1%). In contrast, peroxidases (PODs) showed slightly increased activity at low concentrations and significant reduction at higher concentrations. Also, H2O2 content and malondialdehyde (MDA) content were increased in treated Azotobacter cells. The native isolates of Azotobacter sp. strain greatly increased the vigour index and germination rate of H. sabdarriffa up to 90% as compared to only 50% in the untreated control. We believe the response of Azotobacter, treated with H2O2 was probably related to the different protective effects of antioxidant enzymes in this strain. The ability of the bacterium to respond and survive at exposure to H2O2 during logarithmic growth could be important during colonization of the root surface when the cells are presumably entering into an actively growing phase