| Paulownia as a unique native tree species in China,it is one of the important multipurpose fast-growing trees in China because of its high fertility,rapid growth,light and beautiful texture of wood,and rich in flavonoids and alkaloids,which are commonly used in sand control,landscaping,furniture making,medical and other production practices.Due to global warming and other factors,drought has become one of the most important abiotic stresses affecting plant growth and development,which restricts the growth and development of Paulownia and related pro`duction practices.Therefore,it is important to study the physiological mechanisms of paulownia under drought stress.In this study,the physiological changes of diploid and tetraploid Paulownia aibiphloea were investigated during drought stress and the metabolomic changes before and after drought treatment by using the treatment of continuous natural drought.The main results were as follows:(1)The morphological changes of diploid and tetraploid Paulownia aibiphloea were observed during different drought periods and after rehydration treatment.With the increase of drought,both diploid and tetraploid Paulownia aibiphloea wilted,and the tetraploid Paulownia aibiphloea was more significant,after rehydration,both regained their firmness.(2)The photosynthetic system of both diploid and tetraploid Paulownia aibiphloea responded under drought stress.The net photosynthetic rate(Pn),transpiration rate(Tr),stomatal conductance(Gs),chlorophyll a content(Chla),chlorophyll b content(Chlb),and total chlorophyll content(Chl)of diploid and tetraploid Paulownia aibiphloea leaves all decreased with increasing drought and increased after rehydration.Water use efficiency(WUE)showed a continuous increase throughout the experiment.The intercellular CO2 concentration(Ci)showed a trend of increasing and then decreasing during the drought treatment,and further decreased after rehydration.The Pn,Tr,Gs,WUE,Chla,Chlb,and Chl of the leaves and roots of tetraploid Paulownia aibiphloea were overall higher than those of diploid Paulownia aibiphloea throughout the experiment,while Ci was the opposite.This indicates that the photosynthetic capacity of Paulownia aibiphloea tetraploid is greater than that of diploid under the same drought conditions.(3)Under drought stress,the physiological responses of diploid and tetraploid Paulownia aibiphloe leaves and roots were mainly reflected in two aspects of osmotic substances and antioxidants.Among them,the water content of both diploid and tetraploid Paulownia aibiphloe leaves and roots decreased as the degree of drought increased,and both rebounded after rehydration.Proline(Pro)content,soluble protein(SP)content and soluble sugar(SS)content of leaves and roots showed an overall increasing trend,SS of roots showed a trend of rising and then falling,and SP of roots showed a trend of rising and then falling.After rehydration,Pro,SS and SP of leaves fell back,and Pro,SS and SP of roots continued to rise.The malondialdehyde(MDA)content,hydrogen peroxide(H2O2)content,catalase(CAT)activity,and peroxidase(POD)activity of leaves and roots as a whole increased with the deepening of drought,and the superoxide anion(O2-)content of leaves and roots showed a trend of first increasing and then decreasing.After rehydration,MDA,H2O2,CAT,and POD of leaves and roots all fell back,and POD of leaves further increased and O2-of leaves and roots further decreased.During the whole experiment,the overall water content,Pro,SS,SP,H2O2,CAT,and POD of the leaves and roots of the tetraploid Paulownia aibiphloe were higher than those of the diploid Paulownia aibiphloe,while MDA and O2-was the opposite.This indicates that the tetraploid Paulownia aibiphloe produces more osmoregulatory substances and less harmful substances under drought conditions,and the antioxidant system is more active and the cells are less damaged.(4)Differential analysis of metabolomic data showed that there were 277 and 225 differential metabolites between diploid and tetraploid Paulownia aibiphloe before and after drought stress treatment,respectively,and 316 and 167 differential metabolites between diploid and tetraploid Paulownia aibiphloe before and after drought stress treatment,respectively.KEGG analysis of metabolomic differential metabolites showed that 61 of the differential metabolites of the diploid Paulownia aibiphloe before and after drought treatment were annotated to 76 metabolic pathways led by purine metabolic pathway and amino acidt RNA biosynthesis pathway.56 differential metabolites of the tetraploid Paulownia aibiphloe before and after drought treatment were annotated to 58 metabolic pathways led by the amino acid-t RNA biosynthesis pathway and the glucosinolate biosynthesis pathway.66 differential metabolites between diploids and tetraploids of Paulownia aibiphloe were annotated to 71 metabolic pathways led by the biosynthetic pathway of arginine and the D-amino acid metabolic pathway before drought stress treatment.40 of the differential metabolites between diploids and tetraploids of Paulownia aibiphloe after drought stress treatment were annotated to 54 metabolic pathways led by amino acid-t RNA biosynthesis pathway and glucosinolate biosynthesis pathway.(5)97 metabolites related to drought stress response were screened in Paulownia aibiphloe.Among them,30 were up-regulated and 67 were down-regulated,with the most metabolites distributed in the primary category of amino acids and their derivatives.KEGG enrichment analysis revealed that 23 metabolites were annotated to 35 metabolic pathways led by the tryptophan metabolic pathway,the biosynthetic pathways of tropane,piperidine and pyridine alkaloids.(6)75 metabolites associated with different ploidy differences were screened in Paulownia aibiphloe.Among them,41 were up-regulated and 34 were down-regulated,and the most metabolites were distributed in the flavonoid level category.KEGG enrichment analysis revealed that 14 metabolites were annotated to 32 metabolic pathways led by linoleic acid metabolic pathway and glucosinolate biosynthesis pathway. |
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