Evaluation of the enzymatic and non-enzymatic antioxidant defense system of artichoke root extract against cadmium

Plants have many defense systems to overcome stresses, especially heavy metals. Some heavy metals are part of pigments and enzyme compounds and are also essential elements. In concentrations higher than plants' physiological needs, they are toxic for plants, but some heavy metals such as cadmium and lead are even unnecessary. At low concentrations, they harm plants, and for this reason, heavy metals are considered stressors. Based on this, it is imperative to investigate these metals' effects on plant oxidizing enzymes' activities. In this research, in order to investigate the reaction of oxidizing enzymes and non-oxidizing factors against the stress caused by cadmium (Cd), the required artichoke after being prepared from the mountains of Kurdistan in the presence of phosphate buffer, pH 7 and PMSF 0.02 solution as Protease inhibitor was homogenized and after centrifugation at 3000 g and 15000 g, the upper clear solution was used as a crude extract and for subsequent measurements. In the performed tests, the effect of different concentrations of cadmium chloride (CdCl2) were measured on the content of proline (Pro), phenolic compounds (Ph.C) and the activity of antioxidant enzymes such as phenyl-alanine-ammonialyse (PAL), catalase CAT), superoxide dismutase (SOD), ascorbate peroxidase (APX), guaiacol peroxidase (GPX) and polyphenol oxidase (PPO) of artichoke root. This project was carried out in the form of a completely randomized design in three replications in vials containing three milliliters of artichoke root extract with seven treatments, in which the first group was treated as a control in the presence of distilled water only. The second group was exposed to 0.25 mM CdCl2, the third, fourth, fifth, sixth, and seventh groups were exposed to 0.5, 1, 2, 5, and 10 mM CdCl2, respectively, for 10 minutes. The samples were treated at room temperature of 20 to 25 degrees and 10 minutes of natural light. Then, the activity level of each antioxidant enzyme and the level of Pro and Ph.C was measured separately. In this research, at first, the distribution diagram of the data (enzyme or protein activity against different levels of Cd) was drawn, and then various linear and non-linear regression equations were used to fit the data. In the next step, according to the best type of equation and analysis of the response type of GPX, SOD, APX, protein, Pro and Ph.C was used from nonlinear regression analysis (power, hyperbolic, asymptotic exponential and asymptotic growth models) and to express the response of enzyme activity of PPO, CAT and PAL to different levels of Cd were used from the beta model.
All models indicated Cd's stimulating effect on the studied enzymes. The research results showed that the activity of all SOD, APX, CAT, PPO, GPX, and PAL enzymes as well as the content of Pro and Ph. C increased significantly after Cd treatment. Using five non-linear regression models, the highest activity of APX enzyme at a concentration of 4.6 mM (asymptotic exponential model), GPX enzyme at a concentration of 12.3 mM (asymptotic exponential and asymptotic growth models), SOD enzyme at 14.3 mM (asymptotic growth model) was interpolated. In addition, the most production of Pro and Ph. C was obtained at concentrations of 13.6 and 14.3 mM Cd using the asymptotic and asymptotic growth models, respectively. The highest activity of the PPO enzyme was at 8 mM, CAT at 4.8 mM, and the maximum activity of PAL was at 1.4 mM. The results showed that Cd, due to the induction of oxidative stress and the increase in free radical production, leads to an increase in the content of proline, phenolic compounds, and the activity of antioxidant enzymes in artichoke roots. Further changes in the activity of these enzymes during growth indicate the presence of enzymatic regulatory mechanisms in artichoke roots against heavy metals such as cadmium. Enzymatic antioxidant defense systems, Pro and Ph. C play a crucial role in the response of artichoke roots to heavy metal cadmium stress.
In general, results showed that Cd, due to the induction of oxidative stress and the increase in free radical production, leads to an increase in the content of proline, phenolic compounds, and the activity of antioxidant enzymes in artichoke roots. Further changes in the activity of these enzymes during growth indicate the presence of enzymatic regulatory mechanisms in artichoke roots against heavy metals such as cadmium. Enzymatic antioxidant defense systems and Pro and Ph. C are crucial in the response to heavy metal cadmium stress of artichoke roots.