Ethylene biosynthesis is involved in the early oxidative challenge induced by moderate Cd exposure in Arabidopsis thaliana

The stress hormone ethylene is known to be crucial for the survival of adverse environmental stimuli. Cadmium (Cd), a toxic metal, increases ethylene biosynthesis through an upregulated expression of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS) isozymes, ACS2 and ACS6. In this study, wild-type (WT) and acs2-1acs6-1 double KO-mutant Arabidopsis thaliana plants were exposed to moderate (5 mu M) and more severe (10 mu M) Cd stress. The short-term influence of the Cd-induced ethylene production on growth and different oxidative stress parameters, and the consequent long-term influence on plant acclimation were investigated. Short-term moderate Cd stress conditions elicited enhanced stress-related responses in WT plants compared to the acs2-1acs6-1 mutants. The fresh weight of acs2-1acs6-1 mutant leaves was higher compared to the WT after 72 h exposure to moderate Cd stress. The transcript levels of pro-oxidative and oxidative stress marker genes as well as the expression of GSH1 and GSH2, the enzymes synthesising the antioxidative metabolite glutathione (GSH) were lower in the acs2-1acs6-1 mutant plants compared to the WT. This also resulted in a lower GSH content in the leaves of the acs2-1acs6-1 mutant plants. Severe stress apparently overwhelmed the stress signal sensing system of both genotypes, overruling most of these different responses. Long-term exposure to moderate and severe Cd stress inhibited root and leaf development as well as the reproductive capacity of WT and acs2-1acs6-1 mutant plants without inducing differences between both genotypes, suggesting ethylene independence. We can conclude that ethylene plays an important role in the early oxidative challenge induced by moderate Cd stress in A. thaliana. (C) 2015 Elsevier B.V. All rights reserved.