Potassium channel-oxidative phosphorylation relationship in durum wheat mitochondria from control and hyperosmotic-stressed seedlings

Durum wheat mitochondria (DWM) possess an ATP-inhibited K + channel, the plant mitoK ATP (PmitoK ATP), which is activated under environmental stress to control mitochondrial ROS production. To do this, PmitoK ATP collapses membrane potential (ΔΨ), thus suggesting mitochondrial uncoupling. We tested this point by studying oxidative phosphorylation (OXPHOS) in DWM purified from control seedlings and from seedlings subjected both to severe mannitol and NaCl stress. In severely-stressed DWM, the ATP synthesis via OXPHOS, continuously monitored by a spectrophotometric assay, was about 90% inhibited when the PmitoK ATP was activated by KCl. Contrarily, in control DWM, although PmitoK ATP collapsed ΔΨ, ATP synthesis, as well as coupling [respiratory control (RC) ratio and ratio between phosphorylated ADP and reduced oxygen (ADP/O)] checked by oxygen uptake experiments, were unaffected. We suggest that PmitoK ATP may play an important defensive role at the onset of the environmental/oxidative stress by preserving energy in a crucial moment for cell and mitochondrial bioenergetics. Consistently, under moderate mannitol stress, miming an early stress condition, the channel may efficiently control reactive oxygen species (ROS) generation (about 35-fold from fully open to closed state) without impairing ATP synthesis. Anyway, if the stress significantly proceeds, the PmitoK ATP becomes fully activated by decrease of ATP concentration (25-40%) and increase of activators [free fatty acids (FFAs) and superoxide anion], thus impairing ATP synthesis. The manuscript deals with the effect of the mitochondrial ATP-sensitive potassium channel (PmitoKATP) activity on the oxidative phosphorylation (OXPHOS) in durum wheat. The PmitoKATP may collapse membrane potential (ΔY) in such a manner to dampen mitochondrial ROS production. So, the channel may act as a mitochondrial and cell defence mechanism under environmental/oxidative stress condition. Interestingly, ΔY collapse may occur without affecting mitochondrial ATP synthesis via OXPHOS in mitochondria from seedlings grown under both control and moderate hyperosmotic stress condition, while under severe hyperosmotic stress OXPHOS is impaired. Results suggest a major role of the channel at the early phase of the stress when it may control ROS generation without affecting ATP synthesis. © 2011 Blackwell Publishing Ltd.