Effects Of Exogenous Melatonin On Physiological Indicators And Transcriptome Analysis Of Rice Seedlings Under Copper Stress

Copper is one of the essential trace elements in animals and plants,but excessive copper will affect the growth and development of animals and plants and cause environmental pollution.To study the physiological and biochemical indicators and transcriptome analysis of rice under copper stress,it is necessary to analyze the effects of copper on rice.Toxicity mechanisms and mitigation methods of stress play an important role.Melatonin is an indole substance of tryptophan,which not only participates in growth metabolism,promotes seed germination and root structure,but also scavenges reactive oxygen species and relieves biotic and abiotic stress damage to plants.However,the mechanism of action of melatonin in plant responses to copper stress is still unclear.In this paper,two rice varieties Nipponbare(sensitive)and Wuyunjing 7(tolerance)with significant differences in copper tolerance were used as research materials.The effects of melanin on the antioxidant system of rice under copper stress were studied.The main results are as follows:1.The changes of biomass,antioxidant system and expression of copper transport-related genes of Nipponbare and Wuyunjing 7 under copper stress were studied.The results showed that Nipponbare seedlings showed obvious toxicity under copper stress.Compared with the control group,the leaves curled and turned yellow,the leaf sheaths turned yellow,and the roots turned yellow.However,Wuyunjing 7under the same treatment at the same time only showed yellowing of lower leaves and yellowing of leaf sheaths,and the root system was not as seriously damaged as Nipponbare.Secondly,copper stress also inhibited the accumulation of fresh weight and dry weight of roots,sheaths and leaves of Nipponbare seedlings,but for Wuyunjing 7,the fresh weights of roots,sheaths and leaves were significantly inhibited,while the accumulation of dry matter in leaf sheaths increase,indicating that the inhibition effect of Nipponbare was significantly higher than that of Wuyunjing 7.Further studies have shown that copper ions can cause a large amount of ROS to accumulate in Nipponbare and Wuyunjing 7 plants,cause peroxidative damage to rice,increase MDA content,activate the antioxidant system,and greatly increase the activities of APX,POD,SOD and other enzymes,but still Nipponbare was more seriously damaged.At the molecular level,it was also found that the copper chaperone protein q ATX,heavy metal transporter and COPT transporter all responded to copper ion stress,and their expression patterns were different in different parts of different varieties.2.Using transcriptome high-throughput sequencing technology to analyze the differentially expressed genes and their functional enrichment of Nipponbare and Wuyunjing 7 under copper stress.The results showed that under copper stress,Nipponbare screened a total of 9051 genes,and Wuyunjing 7 screened a total of 5884 differentially expressed genes.GO enrichment analysis and KEGG functional annotation analysis found that in both Nipponbare and Wuyunjing 7,the differentially expressed genes were concentrated in plastids,thylakoids and photosynthesis after copper stress.In addition,the differentially expressed genes of the two are also related to peroxisomes,which further proves that the introduction of copper ions into plants causes oxidative stress and a sharp increase in ROS levels.3.After exogenous application of melatonin,the root length and root fresh weight of Nipponbare and Wuyunjing 7 seedlings in the copper treatment group increased,the absorption of nutrients increased,the height of Nipponbare seedlings increased significantly,and the seedlings increased significantly.The fresh weight and dry weight increased significantly,the number of leaf curls and the degree of curling were also significantly reduced,and the copper poisoning phenomenon of Wuyunjing7 was also reduced.Nipponbare and Wuyunjing 7 decreased the MDA content and the degree of membrane lipid peroxidation,and the APX,POD and SOD enzyme activities of Nipponbare were also significantly decreased.It can be seen that exogenous melatonin can alleviate the phenomenon of copper toxicity in rice and increase the resistance of rice to copper stress.