Preliminary Study On The Chemical Regulation Mechanism Of Perilla Frutescens Responses To Cadmium Stress Condition

Phytoremediation is an effective way to control heavy metals pollution in soil.The screening of hyperaccumulators and enhancement of tolerance and enrichment capacity are currently hot issues in phytoremediation research.In this study,a hydroponic experiment was conducted with the concentration of cadmium at 0,2,5 and 10 mg/L on Perilla frutescens.Samples were taken at 0,7,14 and 21 days of cadmium treatment to analyze the cadmium content in roots,stems,and leaves of Perilla frutescens,as well as organic chelating ligands(organic acids,glutathione,phytochelations,etc.),enzymes class and non-enzymatic antioxidants.From the perspective of cadmium accumulation,transportation and detoxification,the chemical regulation mechanism of cadmium hyperaccumulation in Perilla frutescens was revealed.In this study,we aim to find the measures to enhance the capacity of cadmium enrichment in Perilla frutescens,further to establish the phytoremediation technology for cadmium polluted soil.The results are as follows:(1)The plant height,root length and biomass of Perilla frutescens showed an upward trend with the increase of hydroponic time,but decreased with the increasing cadmium concentration,this indicated that cadmium stress inhibited the growth of Perilla frutescens and the germination of the Perilla frutescens’ seed(2)With the increase of cadmium concentration,the total chlorophyll content,root vigor,activities of POD and CAT decreased significantly,and the activities of SOD and MDA increased obviously.These suggested that cadmium stress enhanced the ability of the plant for scavenging free radical,and reduced the scavenging ability for H2O2,and exacerbated the peroxidation process of membrane lipid.(3)Under cadmium stress conditions,the hormone content in leaf of Perilla frutescens changed obviously.ZR content increased in the early stage and decreased in the later period of stress,the content of IAA was lower than that of the control.GA content decreased with the increasing of stress time,and the content of ABA increased significantly with the increasing time and cadmium concentration.(4)Under cadmium stress condition,the cadmium content in the organs of Perilla frutescens performed in the order of root>stem>leaf.And the cadmium content in roots,stems and leaves of the plant increased with the increasing of treatment time.The contents of cadmium were also significantly differed among cadmium treatment levels(p<0.05).(5)The dynamics of organic acid content in various organs under cadmium stress condition indicated that oxalic acid,tartaric acid,succinic acid,citric acid and acetic acid in roots,stems and leaves accounted for more than 95%of the total organic acids in the plant,and the contents of acetic acid,ascorbic acid pyruvic acid and fumaric acid were relatively low.The average content of organic acid was significantly different among the organs of Perilla frutescens(p<0.05),which showing in stem(13530.2 μg/g)>leaf(9963.7 μg/g)>root(8676.7 μg/g).(6)The dynamic analysis of GSH and PCs contents in different organs of Perilla frutescens showed that the non-protein thiol compounds in the roots and stems mainly existed in the forms of GSH,PC2,PC3 and PC4 under cadmium stress,while GSH,PC2 and PC3 were existed in the form of GSH,PC2 and PC3.The total contents of the non-protein thiol compounds in organs were in the order of stem>root>leaf.(7)Under the different treatments,the PCs-Cd was detected in roots and stems of Perilla frutescens,which mainly existed in the form of PC2-Cd.The PC2-Cd content in root,stem and leaf of the plant increased with the increasing of cadmium concentration and treatment time.The PC2-Cd content in different parts of Perilla frutescens showed in the order of stem>leaf>root.