Tolerance And Accumulation Mechanism In Response To Manganese Stress In Different Populations Of Chenopodium Ambrosioides L.

Manganese（Mn）is one of vital trace element in biological tissues.While once excessive manganese was uptaken,it will affect the growth and development of plants.Manganese toxic will result in stunted growth and leaf yellowing,curling and browning,as well as inhibitate the photosynthetic and respiration of plants.Chenopodium ambrosioides L.is an invasive perennial herb,native to Tropical America,spreadingly distributed in most manganese ore area in eastern and southern China.Chenopodium ambrosioides can accumulate large amount of manganese with its’ excellent reproductive capacity.In previous studies of our laboratory,the nationwide 22 populations of Chenopodium ambrosioides can be divided into 2 groups:group 1 is from central and southwest China,group 2 is from Jiangsu and Anhui,the first group had epigenetically differentiated into polluted population and non-polluted population.In this study,we compared the tolerance and accumulation capacity of the three populations of Chenopodium ambrosioides:polluted and non-polluted populations in group 1（XC,CS）and non-polluted population in group 2（WH）.Besides,we analyzed the transcriptome expression of the three populations under different Mn treatment,and identified several differential expressed metal transporter genes.The cause of Mn tolerance difference between the two Chenopodium ambrosiodes ecotypes are explained.The following results are obtained:1.The phenotypes and growth parameters（the relative root elongation and relative growth rate of shoot fresh weight）under different manganese treatment were analyzed to compare Mn tolerance XC,CS and WH.The results showed that the growth of XC and CS were significantly greater and higher than WH.In addition,under the treatment of 5 mM Mn,the Mn concentration in the leaves of XC and CS populations was 12,322 mg·kg^-1 and 10,821 mg·kg^-1,respectively,and the transportation factor reached 1.52 and 1.60,respectively.The Mn concentration in the leaves of WH populations was 9,405 mg·kg^-1,and the transportation factor was 1.23,which was significantly lower than that of XC and CS.The above results showed that XC and CS populations had higher Mn tolerance and stronger Mn accumulation and transport capacity compared with WH populations.2.While analyzing the effects of Mn treatment on photosynthesis,oxidative damage and glucose metabolism of XC,CS and WH populations.The results showed that the contents of chlorophyll a,chlorophyll b and carotenoids in XC and CS were significantly higher than those in WH under 5 mM or 10 mM Mn treatment.By comparing the net photosynthetic rate（Pn）and intercellular CO₂ concentration of leaves,it was found that the decrease of net photosynthetic rate（Pn）in XC and CS under Mn treatment may be caused by stomatal limitation factors,while the decrease of Pn in WH under 10 mM Mn treatment may be caused by non-stomatal factors.The leaf subcellular structure showed that under the treatment of 10 mM Mn,the chloroplast structure of WH population was seriously damaged,and the mesophyll cells showed obvious separation phenomenon,while the leaf subcellular structure of XC and CS population was not damaged.The results of H₂O₂ and MDA content showed that the oxidative damage suffered by WH population was significantly higher than that suffered by XC and CS under high concentration of Mn,and when the Mn concentration was 10 mM,the content of MDA and H₂O₂ was 2.1,1.7,2.5 and 2.9 times that of XC and CS populations respectively.The above results showed that compared with XC and CS populations,the degree of oxidative damage of WH population under Mn stress was more serious,and its photosynthetic system was more sensitive to Mn stress.3.To estimate genes related to differences in Mn tolerance and detoxication ability,we used Illumina Novaseq high-throughput sequencing technology to analyse the transcriptome of the two Chenopodium ambrosioides ecotypes in response to manganese treatment.A total of 140,013 assembled unigenes were obtained from Chenopodium ambrosioides and 50,207 unigenes were assigned into 24 KOG functional categories,while 59,714 unigenes were assigned into 21 GO functional classification.The cDNA library was constructed for the two Chenopodium ambrosioides ecotypes with control and 5 mM manganese treatment and then sequenced with Illumina Novaseq sequencing technology and mapped with de novo transcriptome of Chenopodium ambrosioides.The differentially expressed unigenes were then assigned to GO function and KEGG pathway annotation and enrichment analysis.In XC5 vs XC0,CS5 vs CS0 and WH5 vs WH0,5797,5167 and 4295 differentially expressed unigenes were found respectively.Under control and Mn treatment.the difference in gene expression among XC,CS and WH is consistent with their genetic sources,that is XC and CS possess the same genetic source.with smaller DEGs between them,while WH belongs to another genetic source.Mn inhibited the activity of related genes such as starch synthesis and decreased carbohydrate accumulation in the root of chenopodium ambrosioides.Specific and significant enrichment of XC population in flavonoid biosynthesis,lysine biosynthesis and 2-Oxocarboxylic acid metabolism pathways,support the result that XC population has better Mn tolerance and detoxication ability.