Water-Deficit Response Is Not Affected by Glutathione Deficiency in <i>Arabidopsis thaliana pad</i>2-1 Plants

Changes in glutathione and ascorbate content,hydrogen peroxide and abscisic acid were studied in developing leaves inwild-type (Col-0) and glutathione-deficient mutant pad2-1 lines of Arabidopsis thaliana over a time periodof 9 days of drought followed by re-watering. Glutathione deficient mutant (pad2-1) presents mechanisms ofacclimation to water stress through the reduction of plant biomass and increasein endogenous concentrations of ascorbate and glutathione. These acclimationresponses to stress appeared along with the first symptoms of stress and wesuggest here that they are regulated by ABA and H2O2.Normally, wild type plants under conditions of stress require an initialresponse phase in which a decrease in antioxidants is observed before reachingacclimation through the increase in levels of antioxidants. pad2-1 is more sensitive to stress and reacts to it; however, it did notsuffer 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 increasesin ABA were observed, however, more sharply in wild-type stressed plants. Low levels of glutathionetogether with high levels of H2O2 may regulate endogenousABA concentrations and could be related to the slow growth rates which wereobserved during the experiment. The results highlighted the double function ofglutathione as an antioxidant and signal molecule and also, the differentresponse patterns of wild-type and pad2-1when faced with drought stress. The results bring new insights to the responsesof pad2-1 under conditions of water stress.