RHIZOBACTERIAL GLUTATHIONE LEVELS AS AFFECTED BY STARVATION AND CADMIUM EXPOSURE

The rhizosphere is a continuously fluctuating environment in which sev ere stresses are put on its inhabitants, and glutathione, a reducing t ripeptide, and related compounds probably have important roles in cell ular protection. In the present study the metabolism of glutathione wa s examined in rhizobacteria subjected to stress. The plant-growth-prom oting rhizobacterium Pseudomonas fluorescens 5.014 and its mutant 5-2/ 4 were exposed to starvation, either by resuspension or exhaustion, an d to cadmium. Glutathione levels, cell protein, and viable count were determined and compared in different conditions. Both starvation and c admium exposure decreased the amount of glutathione in the cell. No ch anges of the glutathione concentration in the medium were observed wit h or without the presence of rhizobacteria, indicating that there was no transport over the cell membrane. The glutathione levels within the rhizobacteria may give valuable information on how different stresses affect the bacteria. In this study, the involvement of glutathione in the increased stress resistance earlier observed in nutrient-starved P. fluorescens was not supported. The concentration of bacterial gluta thione is suggested as a possible marker for rhizosphere competence, w hich, however, needs to be further evaluated with several strains of r hizobacteria.