Mitigation Effects Of Exogenous Chitosan On Toxicity Oflead Stress To Rice Seedlings

The rapid economic development has brought a great test to environment.Lead pollution is one of the more prominent environmental issues.Crops grown on land contaminated with lead not only limit their own growth and development,but also can transmit lead to humans through the food chain,posing a great threat to human health.Rice is one of the most important economic crops in China.It is very important to ensure the normal growth of rice and reduce the transfer of lead from root to aboveground.Chitosan(CTS)is widely sourced,safe and non-toxic.It can regulate the growth and development of plants and improve the ability of plants to resist stress.It is an ideal material for alleviating lead poisoning in rice.In this study,Guangliang You 676 was used as an experimental material to study the effects of different concentrations of chitosan on the growth and development of rice seedlings under water culture conditions.At the same time,the effects of exogenous chitosan on rice seedlings under lead stress were discussed.The growth and development,physiological and biochemical indicators,hormone content,lead accumulation,and the effect of ascorbate-glutathione circulation system were researched.This study provide theoretical basis and practical guidance for the study of rice lead poisoning regulation.The main results are as follows:1.The results of chitosan screening showed that after treated with different concentrations of chitosan,The catalase(CAT)activity,plant height,root length and biomass of rice seedlings treated with 5 mg·L-1 chitosan were higher than those of other treatments,showing obvious concentration advantage.At which peroxidase(POD)activity in the leaves also suddenly increases,exhibiting high activity.In summary,Rice seedlings treated with 5 mg·L-1 chitosan showed obvious growth advantage.2.Morphological,physiological and biochemical analyses showed that under different concentrations of lead stress,compared to non-chitosan pretreatment,pretreated with chitosan(5 mg·L-1)increased plant height and biomass of rice seedlings,promoted the growth of seedling root.It raised the activity of CAT,proline content and soluble protein content,accelerated the production rate of O2·-in seedlings,reduced malondialdehyde(MDA)content and H2O2 content in seedlings.At the same time,the activity of superoxide dismutase(SOD)was significantly increased at the lead concentration of 50 mg·L-1,and the activity of POD was significantly increased at the lead concentration of 100 mg·L-1.In a word,under lead stress,chitosan pretreatment promoted the growth of seedlings,increased the activity of antioxidant enzymes,reduced the content of harmful substances MDA and H2O2,increased the content of osmoregulatory substances,and alleviated the lead Poisoning in seedlings.3.ASA-GSH circulatory system studies have shown that under lead stress of 50,100 mg·L-1,chitosan pretreatment increases the ascorbate peroxidase(APX),Glutathione reductase(GR),dehydroascorbate reductase(DHAR)and monodehydroascorbate reductase(MDHAR)activity of rice seedlings leaves compared with the non-chitosan pretreatment group.At the same time,it increased GSH(reduced glutathione)content,decreases ASA(reduced ascorbic acid)and DHA(oxidized ascorbic acid)content and increased the ratio of GSH and GSSG(oxidized glutathione).In summary,chitosan pretreatment improved the activity of ASA-GSH cycle-related enzymes,accelerated the removal efficiency of H2O2,improved the recycling rate of antioxidants ASA and GSH,and increased the content of antioxidant GSH.4.The results of hormone studies showed that under different concentrations of lead stress,chitosan pretreatment increased the contents of cytokinin(CTK),gibberellin(GA)and reduced the content of abscisic acid(ABA)in rice seedlings leaves compared with non-chitosan pretreatment.In summary,chitosan pretreatment can promote seedling growth and delay its aging.5.The results of migration and accumulation of lead showed that under different concentrations of lead stress,compared to the non-chitosan pretreatment group,chitosan pretreatment reduced lead accumulation on aboveground in rice seedlings,reduced the lead transport coefficient,and limited the transfer of lead from roots to shoots.