Investigation of the effects of exogenous gallic acid and/or curcumin treatments on growth, photosynthetic parameters, antioxidant system, and tolerance in wheat seedlings under cadmium or lead stress

In this thesis study, it was aimed to determine the effects of 100 μM exogenous GLA (gallic acid) and 100 μM exogenous CUR (curcumin) applications on tolerance, growth, chlorophyll fluorescence, gas exchange parameters, enzymatic and non-enzymatic antioxidants in wheat (Triticum aestivum L.) exposed to 200 μM Cd (cadmium) or 100 μM Pb (lead) stress. It was observed that there were significant decreases in the relative shoot growth rate (RGR), relative water content (RWC), carbon assimilation rate (A), stomatal conductance (gs), Fv/Fm and Fv/Fo values with the application of Cd or Pb compared to the control. Cd exposure alone increased the activities of glutathione reductase (GR), NADPH oxidase (NOX), and monodehydroascorbate reductase (MDHAR), as well as the contents of dehydroascorbate (DHA) and oxidized glutathione (GSSG), compared to the control group. The addition of GLA to Cd treatments increased the activities of catalase (CAT), peroxidase (POX), ascorbate peroxidase (APX), glutathione peroxidase (GPX), glutathione S-transferase (GST), glutathione reductase (GR), and MDHAR, as well as the content of glutathione (GSH). Meanwhile, the addition of CUR increased the activities of superoxide dismutase (SOD), POX, APX, GPX, GST, NOX, dehydroascorbate reductase (DHAR), and MDHAR, along with the contents of total ascorbate (tAsA) and GSH. Compared to the control group, Pb application alone induced only the activities of CAT, GST, NOX, DHAR, and MDHAR, as well as the content of DHA and GSSG. The addition of GLA to Pb applications increased the activities of SOD, CAT, POX, APX, GPX, GST, GR, NOX, DHAR, and MDHAR, along with the content of GSH. Meanwhile, the addition of CUR increased the activities of POX, APX, GPX, GST, GR, NOX, DHAR, and MDHAR, and also enhanced GSH accumulation. It was determined that there was an increase in H2O2 and TBARS contents, which disrupt the membrane integrity of cells and membrane-bound organelles in wheat leaves exposed to the Cd and Pb stress. With GLA and CUR applications, TBARS (except Pb+GLA) and H2O2 contents decreased and the effects of oxidative damage were mitigated. In conclusion, GLA and/or CUR application played an important role in ameliorating the negative effects of oxidative damage in plants exposed to Cd or Pb stress.