| Pinus massoniana Lamb.is an important timber tree species in Southern China and the main tree species for colophonium in China,which is an important part of the forestry economy in mountainous areas,with strong adaptability,rapid growth,and high comprehensive utilization.Therefore,it is widely planted as a tree species for both timber and colophonium,and becomes one of the pillar industries of forestry.With the global warming and the increasing shortage of water resources,especially the frequent seasonal drought in the south in recent years,it seriously threatens the growth and survival rate of Pinus massoniana,affects the economic benefits of Pinus massoniana forest,and has a significant impact on the sustainable development of Pinus massoniana industry,ecological environment,society and economy.Exploring the drought adaptation mechanism of trees and cultivating drought-resistant strains by directional im Provement are economic and effective measures to deal with drought stress.In this paper,the drought resistance of Pinus massoniana in the second generation seed orchard was evaluated and the drought resistant families were screened according to the growth and morphological indexes under drought stress.Through continuous drought stress,the physiological response,cell morphological changes,transcriptomics and metabolomics differences between drought-resistant families and sensitive families were studied,and then the physiological and molecular characteristics of drought-resistant families in response to drought stress were explored,and the drought resistance mechanism of Pinus massoniana was revealed,which Provided theoretical basis for the cultivation of drought-resistant materials of Pinus massoniana.The main results are as follows:(1)The drought resistance of 54 families of Pinus massoniana in the second-generation seed orchard was evaluated.Among them,the average D value of comprehensive drought resistance in 14 materials such as 19-220,19-242 and 19-249 were 0.644,belonging to high drought-resistant families,and the average D value of comprehensive drought resistance in11 materials such as 19-208,19-223 and 19-248 were 0.275 on average,belonging to drought-sensitive families.According to the growth status,drought-resistant family Pm T(19-242)and drought-sensitive family Pm S(19-223)were selected for subsequent physiological and molecular experiments.(2)The root physiological indexes of Pinus massoniana with different drought resistance changed greatly under drought stress.With the increase of drought stress,MDA content increased,and reached the peak under severe drought.The Pm T and Pm S families were 24.62 nmol/L and 28.41 nmol/L,respectively.SOD activity was the highest in mild drought,reaching 376.88 U/g in Pm T family and 310.41 U/g in Pm S family.PRO content reached the peak in severe drought,and the Pm S family was 328.38 μg/g;The Pm T family was 515.09 μg/g.Mild drought mainly im Proves the activity of Protective enzymes in response to drought stress,removes peroxides,and severe drought mainly increases osmotic adjustment content to resist and adapt to drought stress(3)Under drought stress,the morphological changes of root cells of Pinus massoniana with different drought resistances were obvious.The morphology of light drought cells was slightly deformed,and the dehydration of epidermis and cortex cells was shrunk to varying degrees.The arrangement of columnar cells became looser,and the intercellular space became larger.Severe drought cells rupture and collapse,Pm S family cells rupture damage is more serious,Pm T family damage is relatively light.After rewatering,most of the cortical cells of Pm T family could restore relatively complete morphology.(4)The root transcriptome of Pinus massoniana with different drought resistance was larger under drought stress.The number of DEGs in Pm T family was 10011 compared with Pm S family under mild drought stress,of which 3159 were up-regulated and 6852 were down-regulated.Under severe drought,the number of DEGs in Pm T and Pm S families was6118,of which 1612 were up-regulated and 4506 were down-regulated.The number of differential genes in Pinus massoniana was the highest under mild drought,and the molecular activities in response to drought stress were the most active.GO enrichment analysis of differentially expressed genes showed that DEGs were significantly enriched to three biological functions,metabolism,stimulation response and antioxidant activity under different drought stress levels.These biological function genes were related to the response of Pinus massoniana to drought stress.KEGG enrichment analysis of differentially expressed genes showed that DEGs were significantly enriched in three metabolic pathways under different drought stress levels,namely plant hormone signal transduction,phenyl Propanoid biosynthesis and flavonoid biosynthesis,which were related to the response of Pinus massoniana to drought stress.(5)Under drought stress,the root metabolic groups of Pinus massoniana with different drought resistances were relatively large,and 628 metabolites were detected.A total of 91 differential expression metabolites were identified under mild drought stress(60 upregulated and 31 down-regulated).A total of 97 differentially expressed metabolites(46 upregulated and 51 down-regulated)were identified under severe drought,and 84 differentially expressed metabolites(65 up-regulated and 19 down-regulated)were identified after rehydration.With the deepening of drought stress,the number of differential metabolites responding to drought increased gradually.KEGG enrichment analysis of differentially expressed metabolites showed that DEMs were significantly enriched in three metabolic pathways under different drought stress levels,namely plant hormone signal transduction,phenyl Propanoid biosynthesis and flavonoid biosynthesis,which were related to the response of Pinus massoniana to drought stress and had a key regulatory role. |
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