Study On High Temperature Stress To Metasequoia Glyptostroboides From Seed Germination To Early Seedling

Metasequoia glyptostroboides,as a relict plant that experienced the Quaternary glacial period,can be predicted to have strong tolerance to low temperature.In view of the existence of cross-tolerance mechanism in plants,the trend of global warming and the occurrence of extreme high temperature weather,it is necessary to study the high temperature tolerance and physiological mechanism of M.glyptostroboides,so as to provide a scientific basis of the conservation of rare and endangered relicts.Given the seed germination to seedling stage is the most sensitive period of the life cycle of plants on the environment,so we used M.glyptostroboides seeds as research materials,and continuously treated them under high temperature stress during the whole process of imbibition,protrusion,germination,and seeding formation.Taking the parallel experiments at the optimum temperature as the control,the high temperature tolerance of the seeds during the germination and seedling stages was studied by physiological,biochemical and transcriptome methods.The main results are as follows:1.Fresh and mature M.glyptostroboides seeds have a strong tolerance to high temperature during the seeds germination into the seedling stage,and the high temperature tolerance of the seed germination stage is higher than that of seedlings.It can germinate under the conditions of constant temperature and alternating light with25-38°C,but it can only grow normally at 25-30°C,and yellowing occurs when it exceeds 30°C.Comprehensive germination rate,seedling rate,germination index,vigor index and other seed vigor indicators,32°C was taken as the high temperature stress temperature for the germination and seedling stage of M.glyptostroboides seeds.2.The changes of physiological indexes also proved that the high temperature tolerance of M.glyptostroboides seeds in the germination stage were significantly higher than that of seedlings.At the germination stage,compared with the control group,the contents of soluble protein and superoxide anion,and the activities of ascorbic acid peroxidase and glutathione peroxidase in the seeds of the high temperature stress treatment group were significantly increased;After the seedling stage,the content of proline,soluble protein,superoxide anion,reduced glutathione,and catalase activity in seedlings increased significantly again.3.A total of 75,987 differentially expressed genes were screened.The cellular components,molecular functions,biological processes and pathways with the most enriched differentially expressed genes are "cells and cellular compartments","catalytic activity","metabolic processes and cellular processes" and "protein processing in the endoplasmic reticulum",respectively.4.Upregulation of genes such as Bip,Glc I,Glc II,CNX,ERMan1,SAR1,Sec13/31,Sec23/24,Ero1,PDIs,TRAP,Bap31,and Sec6 in protein folding,recognition,and transport pathways are likely to be key to high temperature tolerance to the seeds germinate into the seedling stage of M.glyptostroboides.Upregulation of genes such as Hsp20,Hsp40,Hsp70,Hsp90,Derlin,Ubx,p97,Derlin,RBX1,Ubc6/7,RMA1,Skp1,Ubc H5,DSK2,and RAD23 in the protein ubiquitination degradation pathway are more likely to be key to the high temperature tolerance of M.glyptostroboides at the seeds germinate into the seedling stage.5.Transcription factors such as b HLH,MYB,MYB-related and NAC also play important regulatory roles in the high temperature tolerance of M.glyptostroboides seeds germinate into the seedling stage.