FIG. 4.

β-Galactosidase activity of rap fusions in the rhizosphere. Hatched bars show values from cells recovered from the maize rhizosphere supplied with PNS. Open bars are values from control cells in sand supplied with PNS, citrate, and all requirements to support the growth of the rap fusions as described in Materials and Methods. Inoculum size for controls was 1 × 10⁴ to 2.5 × 10⁴, similar to the number of cells attached to the seeds. Means and standard deviations from three independent experiments are shown. Units are given as the concentration of 4-methyl-umbelliferone (femtomolar) per CFU.