One of the proposed mechanisms through which plant growth-promoting rhizobacteria (PGPR) enhance plant growth is the production of
plant growth regulators, especially
cytokinin. However, little information is available regarding
cytokinin-producing PGPR inoculation on growth and
water stress consistence of forest container seedlings under drought condition. This study determined the effects of Bacillus subtilis on
hormone concentration, drought resistance, and plant growth under water-stressed conditions. Although no significant difference was observed under well-watered conditions, leaves of inoculated Platycladus orientalis (oriental thuja) seedlings under drought stress had higher relative water content and leaf water potential compared with those of noninoculated ones. Regardless of water supply levels, the root exudates, namely
sugars, amino acids and organic
acids, significantly increased because of B. subtilis inoculation.
Water stress reduced shoot
cytokinins by 39.14 %. However, inoculation decreased this deficit to only 10.22 %. The elevated levels of
cytokinins in P. orientalis shoot were associated with higher concentration of
abscisic acid (ABA). Stomatal conductance was significantly increased by B. subtilis inoculation in well-watered seedlings. However, the promoting effect of
cytokinins on stomatal conductance was hampered, possibly by the combined action of elevated
cytokinins and ABA. B. subtilis inoculation increased the shoot dry weight of well-watered and drought seedlings by 34.85 and 19.23 %, as well as the root by 15.445 and 13.99 %, respectively. Consequently, the root/shoot ratio significantly decreased, indicative of the greater benefits of PGPR on shoot growth than root. Thus, inoculation of
cytokinin-producing PGPR in container seedlings can alleviate the drought stress and interfere with the suppression of shoot growth, showing a real potential to perform as a drought stress inhibitor in arid environments.