“…During the plant response to stresses, a faster apoplastic oxidation of PAs has been supposed to occur, allowed by the concurrent increase of PA secretion and catabolism in the cell wall, and the PA-derived H 2 O 2 has been demonstrated to trigger signal transduction pathways leading to the induction of defense gene expression, stress tolerance, or PCD (Moschou et al, 2008;Tisi et al, 2011a). Recently, the dual role of PAs as either signaling compounds or the source of the second messenger H 2 O 2 has been highlighted, and it has been hypothesized that AOs may have a role in PA/H 2 O 2 balance (Moschou et al, 2008;Tisi et al, 2011aTisi et al, , 2011b. In fact, the coordinated modulation of PA metabolism and secretion in the cell wall may represent a crucial mechanism in the control of the PA-H 2 O 2 ratio, which has been suggested to be a significant player in fixing cell fate and behavior under stress conditions (Moschou et al, 2008;Tisi et al, 2011a).…”