The Toxic Effects Of Heavy Metal Pb²⁺ Stress On Hydrilla Verticillata

Heavy metal of lead has a great deleterious effect on animal and plant,and it has been regarded as one of the carcinogens by the International Agency for Research on Cancer.The toxic effects on the human body which are caused by lead have aroused great concern.However,aquatic plants are good for remediation of heavy metal pollution in water bodies with the advantages of low cost and high ecological efficiency.Therefore,it is of vital importance to study the toxic effects of lead on plants and the mechanism of plant against heavy metal stress.In this paper,the effects of lead stress on phytotoxicity and the mechanism of lead tolerance in plants will be studied.The results will become theoretical basis for the restoration of water pollution in the future.The results are as follows: 1.Effects of lead on physiological and biochemical characteristics of H.verticillata :The researcher studies the changes of lead enrichment,chlorophyll,protein and hydrogen peroxide?H₂O₂?and malondialdehyde?MDA?content in hydrilla verticillata with medium containing different concentrations of Pb²⁺?0,25?mol / L,50?mol / L,100?mol / L and 200?mol / L?for 7 days.The test results show that lead enrichment,H₂O₂,and malondialdehyde?MDA?in hydrilla verticillata will increase with the increasing concentrations of Pb²⁺,and malondialdehyde?MDA?will reach the maximum when the concentration of lead is 100?M,but it can result in the decrease of chlorophyll and protein content in hydrilla verticillata.That is to say lead enrichment in hydrilla verticillata will cause oxidative stress and cell membrane damage,and affect material metabolism of the cells at the same time by using different concentrations of Pb²⁺.In the end,hydrilla verticillata will appear the phenomenon of chlorosis and being yellow and even rot.2.Effects of lead stress on biochemical defense in H.verticillataIn order to study the potential biochemical defense mechanism of plants,the researcher analyzes the changes of the activity of antioxidant enzymes?CAT,POD,SOD?,and the content of vitamin C,vitamin E,glutathione?GSH?and total antioxidant capacity?T-AOC?in H.verticillata under the different concentrations of lead stress after 7 days.The results show that the activity of antioxidant enzymes?CAT,POD,SOD?increases markedly.The activities of SOD and CAT increase first and then decrease,and they reach the maximum when the concentration of lead is 25?M and 100?M respectively,while the activity of POD and the content of T-AOC have a increasing trend with the increasing concentrations of Pb²⁺,and the contents of antioxidant substances,such as vitamin C and glutathione?GSH?also increase.But the content of vitamin E doesn't change obviously under lead induction.At this moment,higher activity antioxidant enzymes and higher content of vitamin C and glutathione?GSH?plays an effective role in getting rid of the reactive oxygen,and slow accumulation of MDA and H₂O₂ in H.verticillata.This shows that antioxidant enzymes and antioxidants play an active role in resistance mechanism of lead stress.3.Effects of different pH treatments on the toxicity of Pb²⁺ of H.verticillataThe paper studies the effects of different pH treatments on the enrichment of Pb,soluble protein,photosynthetic pigment,H₂O₂,malondialdehyde?MDA?,glutathione?GSH?,total antioxidant capacity?T-AOC?and antioxidant enzyme activities?SOD,CAT and POD?and other physiological indicators under Pb²⁺ stress to investigate the mechanism of different pH treatments on the toxic effects of Pb²⁺ in aquatic plants.The results shows that the accumulation of lead in the H.verticillata and pH show a significant negative correlation.Besides,lead accumulation in the H.verticillata will increase at pH of 4.0 and 5.0,but the result will be opposite under alkaline conditions.What's more,the chlorophyll content will reaches the minimum at pH 4.0,but reach the maximum at pH 7.0.The content of soluble protein will reach the maximum when pH value is 7.0 and decrease under acidic and alkaline conditions.While the content of H₂O₂ and MDA will decrease to its lowest value when H.verticillata is treated at pH 6.0 or 7.0.At the same time,the T-AOC content and the activities of SOD,CAT and POD will also reach the lowest value,when pH value is 7.0 because it can make the induction of GSH relatively weak.This indicates that when the pH was in the range of 6.0 to 7.0,oxidative damage to H.verticillata induced by lead stress is less severe.Therefore,we can conclude that Pb²⁺ stress will cause cell oxidative damage to H.verticillata and have the least toxic effect on H.verticillata at pH 6.0 and 7.0.4.Enhancement of Pb²⁺ stress by exogenous abscisic acid?ABA?To study alleviate toxic effects of heavy metals on plants,the researcher analyzes the changes of the contents of protein,chlorophyll,the activity of antioxidant enzyme,GSH and total antioxidant capacity?T-AOC?in H.verticillata by using Pb²⁺ and exogenous abscisic acid?ABA?.The results showes that the content of chlorophyll in H.verticillata will increase along with higher concentration of ABA,and the activity of SOD and CAT will enhance significantly,but the content of MDA will decreased.This phenomenon indicates that H.Verticillata can enhance the ability of defending heavy metal stress and improve its resistance with the help of ABA.In addition,the amount of GSH in H.verticillata treated by ABA and the total antioxidant capacity?T-AOC?content will increase by Pb²⁺ induced.At the same time,the content of GSH and T-AOC will reach stability when H.verticillata was treated by ABA at 5.0?mol / L and 10.0?mol / L,which indicates that the antioxidant enzymes?SOD and CAT?activation and nonenzymatic antioxidant substances play an important role in alleviating the toxicity of Pb²⁺ on H.verticillata and provides the basis for the ability of ABA which can enhance the resistance to Pb²⁺ stress.