Abstract
Changes in glutathione and ascorbate content, hydrogen peroxide and abscisic acid were studied in developing leaves in wild-type (Col-0) and glutathione-deficient mutant pad2-1 lines of Arabidopsis thaliana over a time period of 9 days of drought followed by re-watering. Glutathione deficient mutant (pad2-1) presents mechanisms of acclimation to water stress through the reduction of plant biomass and increase in endogenous concentrations of ascorbate and glutathione. These acclimation responses to stress appeared along with the first symptoms of stress and we suggest here that they are regulated by ABA and H2O2. Normally, wild type plants under conditions of stress require an initial response phase in which a decrease in antioxidants is observed before reaching acclimation through the increase in levels of antioxidants. pad2-1 is more sensitive to stress and reacts to it; however, it did not suffer more oxidative stress than Col-0 plants, even though pad2-1 had higher levels of endogenous H2O2 relative to wild-type. In both water stressed Col-0 and pad2-1 plants increases in ABA were observed, however, more sharply in wild-type stressed plants. Low levels of glutathione together with high levels of H2O2 may regulate endogenous ABA concentrations and could be related to the slow growth rates which were observed during the experiment. The results highlighted the double function of glutathione as an antioxidant and signal molecule and also, the different response patterns of wild-type and pad2-1 when faced with drought stress. The results bring new insights to the responses of pad2-1 under conditions of water stress.
Highlights
IntroductionWater deficit in plants causes an increase in oxidative molecule concentration [1] and depending on both external parameters and endogenous plant factors such as the concentration of phytohormones, and the interplay between these, as well as the oxidative status of antioxidants [2], cellular structures may be affected, causing oxidative stress
The pad2-1 mutation S298N of GLUTAMINE-CYSTEINE LIGASE (GCL), the first enzyme involved in the biosynthesis of glutathione results in lower glutathione content when compared with the wild type, approximately 20% of the wild type [16]
While no significant differences between Col-0 and pad2-1 plants were observed in terms of water relations when subjected to water stress, they did show differences in terms of growth and the time course of the production of the antioxidants: ascorbate, glutathione, H2O2 and ABA
Summary
Water deficit in plants causes an increase in oxidative molecule concentration [1] and depending on both external parameters and endogenous plant factors such as the concentration of phytohormones, and the interplay between these, as well as the oxidative status of antioxidants [2], cellular structures may be affected, causing oxidative stress. While tripeptide thiol glutathione (γ-glutamyl cysteinyl glycine; GSH) fulfils many important functions such as the storage and transport of cysteine, the maintenance of protein structure and function, and the regulation of enzyme activity through the oxidation/reduction of disulfide bonds and glutathionilation, antioxidant defense and redox signaling remain the primary function of this tripeptide [3]-[7]. Many studies have reported that total glutathione concentration as well as the ratio of it reduced to oxidized forms (GSH: GSSG) affects the cellular redox homeostasis during plant development and environmental stress [3] [8] [9]. Low GSH regulates the expression of a wide range of genes, those that encode transcription factors and proteins involved in hormone dependent regulation of plant growth and development
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