Azospirillum baldaniorum Sp 245 inoculation affects cell wall and polyamines metabolisms in cucumber seedling roots

Azospirillum baldaniorum Sp 245 is a model plant growth-promoting rhizobacterium. The first cross-talk with plants takes place within the roots. Roots cells growth is constrained by the primary cell wall (CW). Also, neighboring CW form the apoplast that should affect cells signaling and biochemical messages. Studies on CW phenolic composition ferulate (FA), diferulates (DFA) and p-coumarate and polyamines (PA) metabolisms of A. baldaniorum Sp 245- inoculated roots and on bacterial PA production in culture media should help to understand more about the mechanisms involved in Azospirillum-root association. For this purpose, CW-bound FA, DFA and p-coumarate contents, putrescine (put) and spermidine contents, diamine and polyamine oxidases activities, and H2O2 content of Cucumis sativus roots from dark grown seedlings inoculated with A. baldaniorum Sp 245 were determined. Also, bacterial PA production under constant agitation or static conditions was evaluated. Results showed lesser contents of all phenolics, and higher FA/DFA ratio in CW of inoculated roots that should be responsible for roots growth promotion. Also, the increased put content, DAO activity, and H2O2 production in the roots should be associated to A. baldaniorum Sp 245 growth promotion in early stages. Finally, the participation of both PA in A. baldaniorum Sp 245 biofilm formation was demonstrated.