Transgenic tobacco plants overexpressing polyamine oxidase are not able to cope with oxidative burst generated by abiotic factors

Abstract

The molecular and biochemical mechanism(s) of polyamine (PA) action remain largely unknown. Transgenic tobacco plants overexpressing polyamine oxidase (PAO) from Zea mays exhibited dramatically increased expression levels of Mpao and high 1,3-diaminopropane (Dap) content. All fractions of spermidine and spermine decreased significantly in the transgenic lines. Although Dap was concomitantly generated with H(2)O(2) by PAO, the latter was below the detection limits. To show the mode(s) of H(2)O(2) scavenging, the antioxidant machinery of the transgenics was examined. Specific isoforms of peroxidase, superoxide dismutase and catalase were induced in the transgenics but not in the wild-type (WT), along with increase in activities of additional enzymes contributing to redox homeostasis. One would expect that because the antioxidant machinery was activated, the transgenics would be able to cope with increased H(2)O(2) generated by abiotic stimuli. However, despite the enhanced antioxidant machinery, further increase in the intracellular reactive oxygen species (ROS) by exogenous H(2)O(2), or addition of methylviologen or menadione to transgenic leaf discs, resulted in oxidative stress as evidenced by the lower quantum yield of PSII, the higher ion leakage, lipid peroxidation and induction of programmed cell death (PCD). These detrimental effects of oxidative burst were as a result of the inability of transgenic cells to further respond as did the WT in which induction of antioxidant enzymes was evident soon following the treatments. Thus, although the higher levels of H(2)O(2) generated by overexpression of Mpao in the transgenics, with altered PA homeostasis, were successfully controlled by the concomitant activation of the antioxidant machinery, further increase in ROS was detrimental to cellular functions and induced the PCD syndrome.

Perturbation of Polyamine Catabolism Can Strongly Affect Root Development and Xylem Differentiation

“…8) similarly to ZmPAO overexpression in the cell wall, suggesting that xylem differentiation and PCD induction are governed by a complex regulatory system in which intracellular PAs and apoplastic PAderived H 2 O 2 are likely integrated in coordinated signaling pathways; this is consistent with a previous hypothesis where salinity-induced cell death was proposed to be governed by the PAs/H 2 O 2 ratio (Moschou et al, 2008b). In this regard, Moschou et al (2008aMoschou et al ( , 2008b reported that the balance between the apoplastic PA catabolism versus the intracellular PA levels plays a central role in plant responses to salinity by governing the cell fate decision, leading to either induction of PCD or to tolerance mechanisms. Specifically, it was proposed that lowering the PA anabolism/PA catabolism ratio promotes PCD (S-ZmPAO and RNAi-SAMDC plants), while if PA anabolism predominates over catabolism, PCD fails to occur, allowing simultaneous induction of stress-responsive genes and plant tolerance (wild-type and A-ZmPAO plants).…”

Polyamines: potent modulators of plant responses to stress

“…The apoplastic PAO from maize is best characterized enzyme, which oxidizes carbon at the endo-side of the N 4 -nitrogen of Spd and Spm using FAD as cofactor resulting into the formation of 4-aminobutanal, 1,3-diaminopropane (Dap), and H 2 O 2 and are thus considered to be involved in a terminal catabolic pathway (Fincato et al 2011). Another group of PAO resembles with mammalian PAOs, catalyzing a sequential retro conversion of Spm to Spd and Spd to Put with concomitant production of 3-aminopropanal and H 2 O 2 (Moschou et al 2008). Figure 1.…”

“…DAO is Cu containing enzyme occur at high levels in dicots, particularly pea, chickpea, lentil, and soybean seedlings, loosely associated with cell wall. They catalyzes the oxidation of diamines like Put at the primary amino groups to generate 4-aminobutanal, H 2 O 2 and ammonia (NH 3 ) and the resulting aldehyde is further converted to g-aminobutyric acid (GABA) via D 1 -pyrroline (Moschou et al 2008). In contrast to DAO, PAO is FAD-dependent enzyme and occur at high levels in monocots which oxidizes only higher PAs like Spd and Spm (Sebela et al 2001) classified into families either by terminal oxidation or back conversion in apoplast and peroxisomes, respectively (Moschou et al 2008).…”

“…They catalyzes the oxidation of diamines like Put at the primary amino groups to generate 4-aminobutanal, H 2 O 2 and ammonia (NH 3 ) and the resulting aldehyde is further converted to g-aminobutyric acid (GABA) via D 1 -pyrroline (Moschou et al 2008). In contrast to DAO, PAO is FAD-dependent enzyme and occur at high levels in monocots which oxidizes only higher PAs like Spd and Spm (Sebela et al 2001) classified into families either by terminal oxidation or back conversion in apoplast and peroxisomes, respectively (Moschou et al 2008). The apoplastic PAO from maize is best characterized enzyme, which oxidizes carbon at the endo-side of the N 4 -nitrogen of Spd and Spm using FAD as cofactor resulting into the formation of 4-aminobutanal, 1,3-diaminopropane (Dap), and H 2 O 2 and are thus considered to be involved in a terminal catabolic pathway (Fincato et al 2011).…”

Deregulation of apoplastic polyamine oxidase affects development and salt response of tobacco plants

“…S-ZmPAO transgenic tobacco plants show increased inter-/intracellular levels of the reactive oxygen species (ROS) H 2 O 2 and O 2 .-and expression of antioxidant genes, which are nevertheless insufficient to scavenge these ROS efficiently (Moschou et al, 2008a(Moschou et al, , 2008b. The AS-ZmPAO tobacco young seedlings show tolerance to short-term salt stress, either due to increased PA content or decreased ROS levels from the impaired PA oxidation in the apoplast (Moschou et al, 2008a(Moschou et al, , 2008b.…”