Zeatin derivatives were present in the bacterial suspension
introduced into the soil (Fig. 2) and the concentration of these
hormones increased in roots and leaves of treated plants (Fig. 3)
(although to a lesser extent when only part, rather the entire,
rootzone was treated), suggesting that increased cytokinin concentrations
in planta may be due to the uptake of cytokinins produced
by microorganisms. To determine whether zeatin could
stimulate root amino acid rhizodeposition, synthetic zeatin was
added to the whole root system, which increased amino acid concentrations
in the soil solution (Fig. 5). Exogenous cytokinin
application to both root compartments induced greater effects on
amino acid concentration than did its local application (to one
container), which may be attributable to greater root and shoot
cytokinin concentrations. The stimulation of amino acid rhizodeposition
following cytokinin supply to those roots of both compartments
may be interpreted as a direct local effect.
An alternative explanation is required to account for increased
amino acid concentrations in the soil solution surrounding roots
that were neither treated with cytokinins or bacteria (Fig. 3), a
possible systemic effect on amino acid rhizodeposition. Since
cytokinin concentrations did not increase in the untreated roots