Influence of pathogenic and non-pathogenic bacteria on soybean suspension cells

Co-cultivations of plant suspension cultures of soybean (Glycine max) with compatible phytopathogenic (Pseudomonas syringae pv. glycinea), incompatible phytopathogenic (Pseudomonas syringae pv. tomato), and different non-pathogenic (Erwinia herbicola, Escherichia coli) bacteria were carried out. Growth and viability (triphenyltetrazolium chloride activity) of plant cells and bacteria as well as enzyme activities of peroxidase (PO), polyphenoloxidase (PPO), and phenylalanine ammonialyase (PAL) within the plant cells were investigated over an incubation period of 7 days. The compatible pathogen inhibited growth and viability of the plant cells after 1 day and led to the death of the majority of the plant cells by the seventh day. In contrast, the incompatible pathogen directly reduced growth and viability of the soybean cells and caused a strong induction of enzyme activities of PO and PAL to more than 4 times of the untreated control by the seventh day. The epiphytic bacterium Erwinia herbicola caused a slight inhibition of growth and viability of the plant cells after the second day of co-cultivation. The PO activity increased in the same manner as in the incompatible interaction. The saprophytic Escherichia coli strain had a negligible influence on soybean suspension cells. All the bacteria tested except for Escherichia coli multiplied rapidly during cocultivation and reached populations of 10(8)-10(9) colony-forming units/ml in the stationary phase. The results from this study demonstrate that the soybean suspension cells react differently to compatible, incompatible and saprophytic bacteria.