Inoculation of Brassica napus L. (canola) with Pseudomonas fluorescens DUS1-27 leads to inhibition of plant growth due to accumulation of hydrogen peroxide

A Pseudomonas fluorescens DUS1-27 isolate was screened for its effect on Brassica napus L. growth over 14 days in a soil-based system and a hydroponic system. Bacterial inoculation enhanced overall plant biomass in the soil-based system, however, plant biomass was reduced in the hydroponic system. Here, we investigate the probable cause for the contrasting plant growth observed for the two systems. Using 3,3'-Diaminobenzadine, total peroxidase activity was visualised in roots of B. napus, and quantified in soil and hydroponic growth media. Amperometry was used to quantify levels of H2O2 in the hydroponic growth media. Quantitative real-time PCR was used to determine catalase gene expression levels in both B. napus roots and P. fluorescens. Total peroxidase activity and H2O2 levels in the hydroponic growth media were higher in plants inoculated with the P. fluorescens isolate. Catalase gene expression in B. napus and P. fluorescens was up-regulated in both organisms when co-cultured in a hydroponic system. Pseudomonas fluorescens is capable of enhancing the growth of B. napus in a soil-based system, whereas in a hydroponic system its addition leads to growth inhibition due to the increased levels of H2O2 in the system.