Effects Of Copper Or Iron Stress On ASA-GSH Cycle In Wheat Seedling Leaves

The development of heavy metal mineral resources,metal smelting and processing and the discharge of “three wastes” have led to an increase in environmental pollution of heavy metals,among which heavy metals has a toxic effect on plants.Copper(Cu)and iron(Fe)are the most common heavy metals and play important role in the normal physiological processes of plants.Once the plants absorbed excessive amounts of Cu and Fe,they would be poisoned and produced reactive oxygen species(ROS).ROS caused oxidative damage,which inhibited plant growth and could cause death in severe cases.Ascorbate(ASA)-Glutathione(GSH)cycle had an irreplaceable role in plants resisting oxidative damage.In this experiment,wheat(Triticum aestivum L.)was used as material to study the growth index,antioxidant activity and ASA-GSH of wheat seedlings treated with different concentrations of copper chloride(Cu Cl2)and ferric chloride(Fe Cl3),and it investigated the effects of cycling on the toxicity of heavy metals Cu and Fe in wheat seedlings and the response of ASA-GSH cycle to heavy metal toxicity.The main results are as follows:1.Under the stress of Cu and Fe,the growth of wheat seedlings was obviously abnormal,and the biomass of wheat seedlings was significantly inhibited.The root tolerance index of wheat seedlings was less than 1,Cu was more toxic to wheat seedlings than Fe in the same concentration.Cu and Fe contents in roots and leaves of wheat seedlings increased with the increase of metal concentration in Cu and Fe treatment,and the root accumulation was significantly higher than that of leaves.Heavy metal treatment imbalanced the nutrient elements sodium(Na),potassium(K)and calcium(Ca)in wheat seedlings.2.The treatment of Cu and Fe significantly induced the accumulation of ROS in the leaves of wheat seedlings,which increased enhanced malondialdehyde(MDA)contents and the peroxidation of membrane lipids,and then led to the increase of membrane permeability.Cu treatment resulted in a decrease in the relative water content of wheat seedling leaves,and Fe treatment had no significant effect on this parameter.Superoxide dismutase(SOD)and catalase(CAT)activities decreased with the increase of Cu concentration,and that showed an increasing trend in Fe treatment.The activity of peroxidase(POD)increased with the increase of metal concentration in the wheat leaves stressed by Cu and Fe,which enhancement was higher than Cu.3.Total ASA and ASA contents increased in the leaves treated with Cu and Fe.With the increase of Cu and Fe concentration,dehydroascorbic acid(DHA)content accumulated gradually,while this parameter in Cu treatment was significantly higher than that in Fe.Cu treatment resulted in a decrease in the ASA/DHA ratio,and showed a tendency to rise first and then fall in the Fe treatment.GSH content in Cu treatment increased gradually with the increase of metal concentration,and the accumulation of GSH in Cu treatment was more than that in Fe treatment.Oxidative glutathione(GSSG)content in wheat leaves increased first and then decreased under Cu treatment,but always increased in Fe treatment.The ratio of GSH/GSSG in wheat leaves increased with Cu stress,and this parameter reached the highest point in low concentration Fe treatment,and then decreased gradually.4.Heavy metals(Cu,Fe)led to increased activity of ascorbate peroxidate(APX),ascorbate oxidase(AAO),and Glutathione reducase(GR),but high concentrations of Fe inhibited GR activity.Cu would promote monodehydroascortate reduetase(MDHAR)activity increase,that increased the supply of ASA.High Cu concentration inhibited dehydrooascorbate reductase(DHAR)activity,and Fe showed the opposite effect in these two enzymes.The activity of glutathione peroxidase(GPX)in wheat seedlings enhanced with the increase of metal concentration,and the increase in Fe treatment was higher than that of Cu treatment.The above results show that: Cu or Fe obviously inhibited the growth and biomass of wheat seedlings,and the root tolerance index was less than 1,the toxic effect of Cu on wheat seedlings was higher than that of Fe.Cu and Fe contents in roots and leaves of wheat seedlings increased with the increase of metal concentration in Cu and Fe treatment,respectively,and the root accumulation was significantly higher than that of leaves.Heavy metal treatment imbalanced the nutrient elements sodium(Na),potassium(K)and calcium(Ca)in wheat seedlings.Cu and Fe treatments induced the accumulation of ROS in the leaves of wheat seedlings,which caused the increase of MDA contents and the increase of membrane lipid peroxidation,which led to the membrane permeability and changed relative water content.SOD,CAT and POD enzymes responded differently in wheat seedlings under Cu and Fe stress,which synergistically eliminated ROS.However,high concentrations of heavy metals inhibited oxidase.Heavy metals maintained the redox state of the antioxidant substances ASA and GSH by inducing changes in the activity of ASA-GSH related enzymes,and reduced the content of ROS.However,different heavy metals had different effects on the enzymes involved in their cycling.