Effects Of Ethephon On The Growth And Oil Accumulation Of Camellia Oleifera Fruits

Camellia oleifera is an important woody edible oil tree species in China.Previous study showed that spraying a certain concentration of ethephon before ripening could improve the oil content of Camellia oleifera seeds,but the effects of ethylene on the growth and development of Camellia oleifera fruits and oil synthesis were unclear.In this study,selecting Camellia oleifera ’Huashuo’ as the test material,it is used by field test observation,GC-MS analysis technology,tissue anatomy microscopic observation,transcriptomics and qRT-PCR to carry out the study on the effects of ethylene on the growth and development of Camellia oleifera fruits,seeds internal components,oil synthesis metabolism and key genes related to oil synthesis metabolism.The study aimed to reveal the effects of ethephon spraying on the growth and development of Camellia oleifera fruits and oil accumulation,and to provide scientific basis for the application of growth regulators to regulate the growth and development of Camellia oleifera fruits in order to improve their yield and quality.The main research results were as follows:1.Spraying ethephon affected fruit growth and development of Camellia oleifera at different times.In this study,we sprayed Camellia oleifera with ethephon(1.00 g/L)at different times(30 August,15 September,30 September,and 15 October)to compare the changes in oil content and the effect of fruits and leaves at fruit maturity.Compared to the control group,the oil increased by 0.99%,2.22%,and 2.31%following ethephon spraying on August 30,September 15 and September 30,respectively.There was no significant difference between October 15 and the control group.According to the results,it is suitable to spray ethephon(1.00 g/L)in mid-late September,which had a relatively better effect on increasing oil content.Spraying ethephon significantly promoted the ripening of Camellia oleifera fruits,but did not affect the fresh fruit weight,fresh seed weight,fresh seed rate and pericarp thickness.The chlorophyll content,relative conductivity,and photochemical efficiency(Fv/Fm)were not affected by ethephon spraying.2.Spraying ethephon significantly affected the metabolite content of Camellia oleifera seeds.After 15,30,and 45 days of treatment,the content of soluble sugar,sucrose,reducing sugar,and 1-aminocyclo-propane-l-carboxylic acid(ACC)in the seeds of Camellia oleifera were determined and analyzed.The contents of soluble sugar and sucrose in the seeds showed a trend of increasing and then decreasing.30 days after treatment,the content of soluble sugar and sucrose in the two groups reached their peak.Reducing sugar and ACC contents showed an increasing trend during fruit development,and both treatments were significantly higher than the controls,with 0.25%and 16.71%increase respectively at 45 days after treatment.3.Spraying ethephon had a significant effect on oil and linoleic acid content of Camellia oleifera seeds.We compared the oil and fatty acid content of Camellia oleifera seeds at 15,30,and 45 days after treatment.The result showed that the oil of seeds increased gradually as the fruit development process continued,and ethephon treatments’ significantly increased the oil of seeds.At 15,30,45 days after treatment,the oil of seeds in the treatments were significantly increased by 0.90%,6.39%and 2.22%,respectively,compared with the controls,as evidenced by laser confocal microscopy and transmission electron microscopy experiments.In addition,during fruit development,although the oleic acid content of seeds in both the treatments and controls showed a continuous increase,while the linoleic and linolenic acid contents both showed a continuous decrease.However,the treatment group’s linoleic acid content at fruit maturity was 2.20%higher than that of the control group.4.The expression of key genes involved in fatty acid metabolism were analyzed by ethylene induction.Transcriptome sequencing analysis was performed on Camellia oleifera seed samples at 15,30,and 45 days after treatment.The results of transcriptome sequencing of Camellia oleifera seeds yielded 118.68 Gb of high-quality reads,and a total of 58,716 unigene were obtained by assembly.122 differential genes were screened with Fold Change>2 and P<0.05,among which there were 56 up-regulated genes and 66 down-regulated genes.Annotation analysis of KEGG metabolic pathways showed that differential genes were mainly distributed in signaling pathways such as glucose metabolism,fatty acid metabolism,and phytohormone signaling.Seven differential genes related to lipid synthesis,CoACCase1,CoKAR,CoEAR,CoGPAT,CoFADdelt,Co9WRI1,and CoABAbZIP,were identified.qRT-PCR results further demonstrated that the expressions of these seven genes were significantly increased by ethylene induction.These results suggest that these seven genes may be key genes in the oil synthesis process of Camellia oleifera.In summary,spraying ethephon(1.00 g/L)applied to Camellia oleifera trees in mid to late September can promote fruit maturity and increase oil,which provides a theoretical basis for improving the production of Camellia oleifera by taking full advantage of hormones.