Download enhanced expression and activation of the alternative oxidase

ENHANCED EXPRESSION AND ACTIVATION OF THE ALTERNATIVE OXIDASE
DURING OZONE TREATMENT IN TOBACCO PLANTS
Luisa Ederli (1), Nicola Tosti (2) and Stefania Pasqualini(1)
(1)
Dip. di Biologia Vegetale e Biotecnologie Agroambientali, UNI Perugina ([email protected])
(2)
Istituto di Genetica Vegetale - CNR Perugia
In addition to the cytochrome respiratory pathway, plants display an alternative pathway
that branches from the main respiratory chain at the level of ubiquinone pool
(Vanlerberghe et al., 1997, Annu. Rev. Plant Physiol. Plant Mol. Biol., 48: 703-734); it is not
inhibited by cyanide and does not contribute to the formation of a proton gradient. This
pathway is therefore not coupled to ATP synthesis (Siedow and Umbach, 1999, Plant Cell,
7: 821-831). Electron transfer along this alternative pathway involves only a single protein,
termed alternative oxidase (AOX), which catalyses the four-electron reduction of oxygen to
water. The physiological role of this pathway remains unclear except in the specialized case
of promoting thermogenesis during flowering in aroid spadices (Moore and Siedow, 1991,
Biochim. Biophys. Acta, 1058: 121-140). However, it has been proposed that AOX can
function as a mechanism to decrease the formation of ROI (reactive oxygen intermediate)
under different stress conditions (Hiser and McIntosh, 1990, Plant Physiol., 93: 312-318;
Vanlerberghe and McIntosh, 1992, Plant Physiol., 100: 115-119; Lennon et al., 1997, Plant
Physiol., 115: 783-791). In this work we report the effect of an acute ozone fumigation (150
ppb for 5 h) on cyanide-resistant respiration in Bel W3 tobacco plants. A strong induction
of expression of alternative oxidase was documented 2.5 h after the onset of fumigation.
The increase in mRNA correlated with the increase in AOX protein. Oxygen electrode
measurements in isolated leaf mitochondria revealed that 2.5 h after the onset of
fumigation there was a strong enhancement of alternative oxidase capacity, whereas the
capacity of cytochrome respiratory pathway was significantly reduced. Western blot
analysis showed, at the same time, a decrease of mitochondrial cytochrome c. The results
indicate that O3-induced oxidative stress stimulates AOX in Bel W3 plants as a strategy to
keep low mitochondrial ROI formation thus limiting cell death.