RESUMO
Plants under oxidative stress suffer from damages that have been interpreted as unavoidable consequences of injuries inflicted upon plants by toxic levels of reactive oxygen species (ROS). However, this paradigm needs to be modified. Inactivation of a single gene, EXECUTER1, is sufficient to abrogate stress responses of Arabidopsis thaliana caused by the release of singlet oxygen: External conditions under which these stress responses are observed and the amounts of ROS that accumulate in plants exposed to these environmental conditions do not directly cause damages. Instead, seedling lethality and growth inhibition of mature plants result from genetic programs that are activated after the release of singlet oxygen has been perceived by the plant.
Assuntos
Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/fisiologia , Arabidopsis/genética , Arabidopsis/fisiologia , Estresse Oxidativo , Oxigênio Singlete/metabolismo , Sequência de Aminoácidos , Arabidopsis/citologia , Arabidopsis/crescimento & desenvolvimento , Proteínas de Arabidopsis/química , Morte Celular/efeitos dos fármacos , Mapeamento Cromossômico , Clonagem Molecular , Cosmídeos , Escuridão , Diurona/farmacologia , Regulação da Expressão Gênica de Plantas , Genes de Plantas , Teste de Complementação Genética , Luz , Dados de Sequência Molecular , Mutação , Fases de Leitura Aberta , Complexo de Proteína do Fotossistema II/metabolismo , Folhas de Planta/citologia , Folhas de Planta/efeitos dos fármacos , Folhas de Planta/metabolismo , Espécies Reativas de Oxigênio/metabolismo , Transformação GenéticaRESUMO
The conditional fluorescent (flu) mutant of Arabidopsis accumulates the photosensitizer protochlorophyllide in the dark. After a dark-to-light shift, the generation of singlet oxygen, a nonradical reactive oxygen species, starts within the first minute of illumination and was shown to be confined to plastids. Immediately after the shift, plants stopped growing and developed necrotic lesions. These early stress responses of the flu mutant do not seem to result merely from physicochemical damage. Peroxidation of chloroplast membrane lipids in these plants started rapidly and led to the transient and selective accumulation of a stereospecific and regiospecific isomer of hydroxyoctadecatrieonic acid, free (13S)-HOTE, that could be attributed almost exclusively to the enzymatic oxidation of linolenic acid. Within the first 15 min of reillumination, distinct sets of genes were activated that were different from those induced by superoxide/hydrogen peroxide. Collectively, these results demonstrate that singlet oxygen does not act primarily as a toxin but rather as a signal that activates several stress-response pathways. Its biological activity in Arabidopsis exhibits a high degree of specificity that seems to be derived from the chemical identity of this reactive oxygen species and/or the intracellular location at which it is generated.