The rhizosphere bacterium Variovorax paradoxus 5C-2 containing ACC deaminase does not increase systemic ABA signaling in maize (Zea mays L.)

Soil inoculation with the ACC deaminase-containing rhizobacterium Variovorax paradoxus 5C-2 increased pea (Pisum sativum) growth and yield in both well watered and drying soil, with an attenuation of systemic ACC signaling likely key in the latter case.1 However, inoculated plants also had increased xylem ABA concentrations (which may also promote growth) in drying soil. Possible mediation of ABA levels by V. paradoxus 5C-2 was investigated in two experiments in which maize (Zea mays) growth was promoted. Xylem ABA concentration of both inoculated and uninoculated plants increased similarly as leaf water potential decreased. Furthermore, hormone flow modeling showed a decreased phloem flow of ABA back to the root. Thus Variovorax paradoxus 5C-2 does not intensify ABA signaling in planta.