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

Abstract

An increase in oxygen uptake has been previously described in plant cell suspensions treated with bacteria or bacterial elicitors. These studies, regarding oxygen uptake, have all been undertaken from the perspective of the host plant cell reacting to the invading pathogen. In contrast, here we describe and characterize an increase in oxygen uptake by bacterial cells in response to plant suspensions or autoclaved plant cell filtrates. Autoclaved plant cell filtrates stimulated bacterial oxygen uptake by as much as seven-fold within a few minutes after addition. This oxygen uptake response was proportional to both the concentration of the plant cell filtrate and the concentration of the bacteria. KCN inhibited the bacterial response, suggesting that bacterial respiration may be involved. Unlike the plant oxygen uptake response to bacteria, there was no concurrent H2O2 accumulation and the NADPH oxidase inhibitor, DPI, had no effect on the bacterial response. Streptomycin, an inhibitor of bacterial protein synthesis, inhibited the bacterial oxygen uptake response to the plant cell filtrate. K-252, a protein kinase inhibitor that strongly inhibits the plant oxygen uptake response to bacteria, had no effect upon the bacterial oxygen uptake response. When potato/bacterial cell suspensions were pretreated with either streptomycin or 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 interactions may be attributable to bacteria, which comprise less than 1% of the total cell mass.