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The overexpression of an alternative oxidase gene triggers ozone sensitivity in tobacco plants
Author(s) -
PASQUALINI STEFANIA,
PAOLOCCI FRANCESCO,
BORGOGNI ANDREA,
MORETTINI ROBERTA,
EDERLI LUISA
Publication year - 2007
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/j.1365-3040.2007.01730.x
Subject(s) - alternative oxidase , catalase , apx , peroxidase , reactive oxygen species , biology , nicotiana tabacum , biochemistry , botany , antioxidant , glutathione reductase , horticulture , enzyme , glutathione peroxidase , gene
The alternative oxidase (AOX) of plant mitochondria transfers electrons from the ubiquinione pool to oxygen without energy conservation and prevents the formation of reactive oxygen species (ROS) when the ubiquinone pool is over‐reduced. Thus, AOX may be involved in plant acclimation to a number of oxidative stresses. To test this hypothesis, we exposed wild‐type (WT) Xanthi tobacco plants as well as Xanthi plants transformed with the Bright Yellow tobacco AOX1a cDNA with enhanced (SN21 and SN29), and decreased (SN10) AOX capacity to an acute ozone (O 3 ) fumigation. As a result of 5 h of O 3 exposition (250 nL L −1 ), SN21 and SN29 plants surprisingly showed localized leaf damage, whereas SN10, similarly to WT plants, was undamaged. In keeping with this observation, WT and SN21 plants differed in their response to O 3 for the expression profiles of catalase 1 ( CAT1 ), catalase 2 ( CAT2 ), glutathione peroxidase ( GPX ) and ascorbate peroxidase ( APX ) genes, and for the activity of these antioxidant enzymes, which were induced in WT. Concomitantly, although ozone induced H 2 O 2 accumulation in WT and in all transgenic lines, only in transgenics with high AOX capacity the H 2 O 2 level in the post‐fumigation period was high. The alternative pathway of WT plants was strongly stimulated by O 3 , whereas in SN21 plants, the respiratory capacity was always high across the treatment. The present results show that, far from exerting a protective role, the overexpression of AOX triggers an increased O 3 sensitivity in tobacco plants. We hypothesize that the AOX overexpression results in a decrease of mitochondrial ROS level that in turn alters the defensive mitochondrial to nucleus signalling pathway that activates ROS scavenging systems.