| Natural citral was an important component of plant essential oil,which was widely used in medicine,food,chemical industry and other fields.It had great economic value,development potential,and market demand.Natural citral in China was mainly extracted from Litsea cubeba(Lour.)Pers.,but there were still some restricting factors in the largescale development and utilization of L.cubeba.Therefore,the natural citral market continues to be in short supply.There were more than ten species of natural plants rich in citral,and nearly half of them were belonged to Sect.Camphora(Trew)Meissn.,and the leaves of Sect.Camphora had high oil yield,relative content of main chemical components and leaf biomass.Therefore,Sect.Camphora was one of the new sources of natural citral worth exploring.In this study,the screening work was carried out in Sect.Camphora in its natural distribution,the chemotype differentiation of different propagation progeny,temporal and spatial dynamics of leaf essential oil and citral metabolism of cutting progeny,and metabolic mechanism of leaf essential oil of cutting progeny were studied by using the selected Sect.Camphora with citral chemotype.The main conclusions are as follows:(1)In the natural distribution area of Sect.Camphora,48 Sect.Camphora with citral chemotype trees were obtained from 2017 to 2020 by aroma method,steam distillation and GC-MS,the classification standard of Sect.Camphora was established based on the yield of essential oil and the relative content of citral.8 superior individuals were divided into 4grades,1 first-class superior individual,no second-class superior individual,1 third-class superior individual and 6 fourth-class superior individuals.(2)According to the determination of essential oil of leaves and main chemical components,the yield of essential oil of the sexual reproduction progeny of Sect.Camphora with citral chemotype was 0.64±0.02%～2.10±0.08%,with an average of 1.35%;the main chemical components of leaf essential oil were differentiated into seven chemotypes through cluster analysis;while the cutting propagation offspring kept the essential oil of mother plant characteristic,the results showed that the yield of essential oil of cuttings was1.09±0.11%～1.33±0.10%,with an average of 1.22%,the relative content of citral was43.07%～54.46%,with an average of 49.42%.(3)The overall trend of the yield of essential oil and relative content of Sect.Camphora with citral chemotype were higher in growing season and lower in non-growing season,the highest yield of essential oil was 1.81±0.16% in summer.The dynamic accumulation of essential oils in the leaves of Sect.Camphora with citral chemotype showed a nearly "S" accumulation pattern,and there was a rapid accumulation period of essential oils in the stage before maturity in the tender leaves.The relative content change trend of two isomers of citral were different,which the dynamic changes of the relative contents of geranial and citral overall trend were consistent,and the relative contents of neral relatively stable.A total of 127 main chemical components were isolated and identified from the essential oil of Sect.Camphora with citral chemotype,and the chemical components in each part were mainly alcohols,ketones,aldehydes,alkenes,and so on.The aldehydes were mainly in leaf essential oil,while the olefine were mainly in root essential oil.Chain structure components were mainly in leaf essential oil,while the ring structure components were the mainly in root essential oil.(4)It was found by tissue transparency that the size of oil cells could be considered as the basis for selecting the best month for oil yield,and the density of oil cells could be considered as the basis for selecting superior aromatic resources.Paraffin section method was used to observe that there were oil cells in the buds,leaves,stems,roots and other parts of the cuttings progenies of Sect.Camphora with citral chemotype.The leaf anatomical structure of four chemotypes of C.camphora was different,so the anatomical structure of leaves could be considered as the basis of chemotype differentiation;The osmophilic drops,mitochondria and plastids in oil cells were directly or indirectly involved in the formation of oil sacs.(5)Transcriptomic sequencing of two chemotypes of C.camphora leaves,through KEGG pathway annotations and GO classification,a total of 9 differentially expressed key genes were selected and matched,among which DXS was the key enzyme in terpene biosynthesis,and TPS14 might be the key gene affecting monoterpene synthesis.To sum up,there were individual plants of leaf essential oil rich in citral in Sect.Camphora,it was found that the yield of essential oil and the relative content of citral in the cuttings propagate offspring were able to maintain the superior characteristics of the mother plant.Therefore,Sect.Camphora was ideal newcomers of natural citral resources to relieve the market supply and demand pressure of natural citral.The formation of essential oil was closely related to metabolic activities,showing a specific spatiotemporal dynamic characteristics.According to the spatiotemporal dynamic characteristics of essential oil metabolism,the production could better guided.Under the action of terpenes and monoterpenes key enzymes,essential oil was formed and stored in oil cells,osmiophilic drops and mitochondria in oil cells were directly or indirectly involved in the synthesis of essential oil. |
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