Oxidative metabolism in plant/bacteria interactions: characterization of the oxygen uptake response of bacteria

Ali increase in oxygen uptake has been previously described in plant cell s uspensions treated with bacteria or bacterial elicitors. These studies, reg arding oxy en uptake, have all been undertaken from the perspretive, of the host plant Cell reacting to the invading pathogen. In contrast, here we de scribe and characterize an increase in oxygen uptake by bacterial cells in response to plant suspensions or autoclaved plant cell filtrates, Autoclave d plant cell filtrates stimulated bacterial oxygen uptake by as much as sev en-fold within a few minutes after addition. This oxygen uptake response wa s proportional to both the concentration of the plant cell filtrate and the concentration of the bacteria. KCN inhibited the bacterial response, sugge sting that bacterial respiration may be involved. Unlike the plant oxygen u ptake response to bacteria, there was not concurrent H2O2 accumulation and the NADPH oxidase inhibitor, DPI, had no effect oil dw bacterial response. Streptomycin, an inhibitor of bacterial protein synthesis, inhibited the ba cterial oxygen uptake response to the plant cell filtrate. K-252, a protein kinase inhibitor that strongly inhibits the plant oxygen uptake response t o bacteria, had no effect upon the bacterial oxygen uptake response. When p otato/bacterial cell suspensions were pretreated with either streptomycin o r K-252, the combined plant/bacterial oxygen uptake response was inhibited by 15 or 70 %, respectively. This indicates that as much as 15-30 % of the increased oxygen consumption during plant suspension cell/bacteria interact ions may be attributable to bacteria, which comprise less than 1 % of the t otal cell mass.