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

Polyamine (PA) homeostasis is associated with plant development, growth and responses to biotic/abiotic stresses. Apoplastic PA oxidase (PAO) catalyzes the oxidation of PAs contributing to cellular homeostasis of reactive oxygen species (ROS) and PAs. In tobacco, PAs decrease with plant age, while apoplastic PAO activity increases. Our previous results with young transgenic tobacco plants with enhanced/reduced apoplastic PAO activity (S-ZmPAO/AS-ZmPAO, respectively) established the importance of apoplastic PAO in controlling tolerance to short-term salt stress. However, it remains unclear if the apoplastic PAO pathway is important for salt tolerance at later stages of plant development. In this work, we examined whether apoplastic PAO controls also plant development and tolerance of adult plants during long-term salt stress. The AS-ZmPAO plants contained higher Ca2+ during salt stress, showing also reduced chlorophyll content index (CCI), leaf area and biomass but taller phenotype compared to the wild-type plants during salt. On the contrary, the S-ZmPAO had more leaves with slightly greater size compared to the AS-ZmPAO and higher antioxidant genes/enzyme activities. Accumulation of proline in the roots was evident at prolonged stress and correlated negatively with PAO deregulation as did the transcripts of genes mediating ethylene biosynthesis. In contrast to the strong effect of apoplastic PAO to salt tolerance in young plants described previously, the effect it exerts at later stages of development is rather moderate. However, the different phenotypes observed in plants deregulating PAO reinforce the view that apoplastic PAO exerts multifaceted roles on plant growth and stress responses. Our data suggest that deregulation of the apoplastic PAO can be further examined as a potential approach to breed plants with enhanced/reduced tolerance to abiotic stress with minimal associated trade-offs.

Gémes K ，Mellidou Ι ，Karamanoli K ，Beris D ，Park KY ，Matsi T ，Haralampidis K ，Constantinidou HI ，Roubelakis-Angelakis KA ... -  《-》

Underexpression of apoplastic polyamine oxidase improves thermotolerance in Nicotiana tabacum.

Polyamines (PAs) and hydrogen peroxide (H2O2), the product of PA oxidation by polyamine oxidase (PAO), are potential players affecting plant growth, development and responses to abiotic/biotic stresses. Genetically modified Nicotiana tabacum plants with altered PA/H2O2 homeostasis due to over/underexpression of the ZmPAO gene (S-ZmPAO/AS-ZmPAO, respectively) were assessed under heat stress (HS). Underexpression of ZmPAO correlates with increased thermotolerance of the photosynthetic machinery and improved biomass accumulation, accompanied by enhanced levels of the enzymatic and non-enzymatic antioxidants, whereas ZmPAO overexpressors exhibit significant impairment of thermotolerance. These data provide important clues on PA catabolism/H2O2/thermotolerance, which merit further exploitation.

Mellidou I ，Karamanoli K ，Beris D ，Haralampidis K ，Constantinidou HA ，Roubelakis-Angelakis KA ... -  《-》

An NADPH-Oxidase/Polyamine Oxidase Feedback Loop Controls Oxidative Burst Under Salinity.

The apoplastic polyamine oxidase (PAO) catalyzes the oxidation of the higher polyamines spermidine and spermine, contributing to hydrogen peroxide (H2O2) accumulation. However, it is yet unclear whether apoplastic PAO is part of a network that coordinates the accumulation of reactive oxygen species (ROS) under salinity or if it acts independently. Here, we unravel that NADPH oxidase and apoplastic PAO cooperate to control the accumulation of H2O2 and superoxides (O2·-) in tobacco (Nicotiana tabacum). To examine to what extent apoplastic PAO constitutes part of a ROS-generating network, we examined ROS accumulation in guard cells of plants overexpressing or down-regulating apoplastic PAO (lines S2.2 and A2, respectively) or down-regulating NADPH oxidase (line AS-NtRbohD/F). The H2O2-specific probe benzene sulfonyl-H2O2 showed that, under salinity, H2O2 increased in S2.2 and decreased in A2 compared with the wild type. Surprisingly, the O2·--specific probe benzene sulfonyl-So showed that O2·- levels correlated positively with that of apoplastic PAO (i.e. showed high and low levels in S2.2 and A2, respectively). By using AS-NtRbohD/F lines and a pharmacological approach, we could show that H2O2 and O2·- accumulation at the onset of salinity stress was dependent on NADPH oxidase, indicating that NADPH oxidase is upstream of apoplastic PAO. Our results suggest that NADPH oxidase and the apoplastic PAO form a feed-forward ROS amplification loop, which impinges on oxidative state and culminates in the execution of programmed cell death. We propose that the PAO/NADPH oxidase loop is a central hub in the plethora of responses controlling salt stress tolerance, with potential functions extending beyond stress tolerance.

Gémes K ，Kim YJ ，Park KY ，Moschou PN ，Andronis E ，Valassaki C ，Roussis A ，Roubelakis-Angelakis KA ... -  《-》

Spermidine exodus and oxidation in the apoplast induced by abiotic stress is responsible for H2O2 signatures that direct tolerance responses in tobacco.

Moschou PN ，Paschalidis KA ，Delis ID ，Andriopoulou AH ，Lagiotis GD ，Yakoumakis DI ，Roubelakis-Angelakis KA ... -  《-》

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

Moschou PN ，Delis ID ，Paschalidis KA ，Roubelakis-Angelakis KA ... -  《-》