INOCULATION OF PLANTS WITH A FLAVOBACTERIUM SPECIES RESULTS IN ALTERED RHIZOSPHERE ENZYME-ACTIVITIES

The inoculation of wheat seedlings with Flavobacterium P25 (1 x 10(9)/seedling) resulted in increased activity of four hydrolases: alpha-galactosidase (+40%), beta-galactosidase (+23%), alpha-glucosidase (+18%) and beta-glucosidase (+28%) in the endorhizosphere (rhizoplane and root) by day 14. Neither the release of enzymes from dead P25 cells nor altered enzyme activities expressed by starved P25 cells could account for the changes in activity. Studies to investigate if the changes were due to P25 affecting enzyme production by the indigenous bacterial species, showed that there was no correlation between the increases in activity following inoculation and the numbers of indigenous bacteria expressing the relevant activities. However, whilst the total number of bacteria expressing the four different enzymes were present in approximately equal numbers at the start of the study, this changed as the plant developed so that by the time the plant was 35 days old 60-70% of indigenous isolates expressed alpha-glu and beta-glu but only 10-20% expressed alpha-gal and beta-gal. Inoculation also affected plant root protease activity with inoculated plants expressing only 45% of the activity measured in non-inoculated plants. This may explain the increase in carbohydrase activity in the rhizosphere of inoculated plants.