| Walnut(Juglans regia)is a genus of walnut in the pecan family,and is one of the important nut and edible oil resources in China.Most of its varieties contain unsaturated fatty acids up to 90%,and are also rich in vitamins and calcium,iron,zinc and many other nutrients beneficial to the human body.However,at present,there is an oversupply of walnuts in China,the economic benefits are decreasing,and walnut forests are being abandoned or cut down.Therefore,improving walnut yield and quality through scientific cultivation management measures is an important measure to crack the underutilization of walnut resources in China and help promote the high-quality developmentthe of walnut industry.Plant growth regulators can significantly affect the growth and development of plants,and the appropriate concentration and application time can effectively improve the yield or quality of agricultural and forestry crops.As an important plant growth regulator,paclobutrazol(PAC)has good performance in regulating plant growth and development cycle,promoting crop yield and yield increase,and assisting plant resistance,etc.,while the mechanism of regulating walnut fruit development and nutrients has not been reported.Based on this,this paper takes ’Yu Xiang’ walnuts as the research object and analyzes the effect patterns of different concentrations(100,200 and 400 mg/L)of PAC treatment on the weight and morphological parameters,kernel weight,oil content and the fatty acid fraction of green fruits and drupes of walnuts,and analyzes them by significance test,correlation analysis,cluster analysis,and The measured data were analyzed by significance test,correlation analysis,cluster analysis and TOPSIS modeling analysis,and combined with transcriptome analysis to reveal the effect of PAC treatment on walnut fruit growth and walnut kernel nutrients and the mechanism,and to screen out the PAC treatment conditions that can improve walnut yield and quality.The main results were as follows:(1)Influence pattern of fruit weight and morphology of walnuts treated with PACAt the early stage of oil synthesis,PAC treatment had a certain effect on green fruit weight,drupe weight and kernel weight at the ripening stage,with the most obvious effect of 200 mg/L PAC treatment.green fruit weight,drupe weight and kernel weight at the ripening stage increased by 6.1414 g,1.6417 g and 0.5876 g respectively compared with the control group at 200 mg/L.After different concentrations of PAC treatment,the green fruit shape index and kernel shape index were significantlysuppressed at the early stage of fruit development.The green fruit shape index and drupe shape index of walnuts were significantly suppressed at the early stage of fruit development;the green fruit shape index and drupe shape index at the ripening stage were significantly suppressed by PAC treatment at 100 mg/L and 200 mg/L,while PAC treatment at 400 mg/L had a certain promotion effect.During the period of rapid oil synthesis,PAC treatment resulted in an overall suppression of green fruit weight,drupe weight and kernel weight in ripening fruit.For the green fruit shape index,PAC treatment showed some inhibition in the early stage of fruit development and promotion in the ripening stage.For the drupe shape index,PAC treatment showed an overall inhibition.(2)Effect of PAC treatment on nutrients in walnut kernelsIn the early stage of oil synthesis,the total sugar content of ripe walnut kernels was significantly promoted by PAC treatment,with the highest increase in total sugar content of ripe walnut kernels after 400 mg/L PAC treatment,which increased by 12.7753 mg/g compared with the control group.for soluble protein content,PAC treatment showed a significant promotion in the ripe stage overall,with 100 mg/L and 400 mg /L of PAC treatment showed significant promotion.For total phenolic content,PAC treatments of 100 mg/L and 200 mg/L showed significant promotion at maturity.For the total flavonoid content,the PAC treatment at 400 mg/L showed a significant promotion effect at maturity,with an increase of 1.6608 mg/g compared to the control group.for the oil content,all treatment groups showed a promotion effect at maturity,with the PAC treatment at 200 mg/L showing the most significant effect,with an increase of 4.5976% compared to the control group.The saturated fatty acid content of walnut kernel oil at the ripening stage was inhibited and the unsaturated fatty acid content was somewhat promoted by the PAC treatment at 200 mg/L.During the period of rapid oil synthesis,the total sugar content of walnut kernels at the ripening stage was promoted by the PAC treatment at 200 mg/L.For soluble protein content,200 mg/L PAC treatment was significantly inhibited at the ripening stage.For total phenolic content,the ripening stage treatment group showed a promoting effect.For total flavonoid content,the ripening stage was significantly inhibited after 200 mg/L PAC treatment.For oil content,the ripening treatment group showed a promoting effect,but saturated fatty acid content was significantly inhibited at the ripening stage after 200 mg/L PAC treatment.(3)Multivariate statistical analysis of walnut fruit morphology and nutrientsThe correlation analysis showed that the total sugar content and total flavonoid content in walnut kernels were significantly positively correlated in the control group,the total sugar content was suppressed and the total flavonoid content was promoted after PAC treatment at 100 mg/L and 200 mg/L.The correlation between the two indexes was increased under PAC treatment at 400 mg/L.The correlation between drupe weight and oil content was positive in the control group,while a significant negative correlation was observed in the treated group.Drupe weight was significantly inhibited by PAC treatment at 200 mg/L,while oil content was promoted.The results of the cluster analysis showed that after PAC treatment,the control and treatment groups were distinguished from each other and each sampling node after treatment at the corresponding Euclidean distance,and the treatment groups 2-PAC-200,3-PAC-200,4-PAC-200 and 5-PAC-400,which were often significantly different from the control group at the time of ANOVA,also showed large variability from the control group at the same time that corroborated the results of ANOVA.The results of the TOPSIS analysis showed that the closer the ripening stage was,the higher the overall score of the experimental group was.At the same time,after the PAC spraying treatment at the early stage of oil synthesis,the overall scores of the ripening treatment group were higher than those of the control group,indicating that PAC has a beneficial effect on fruit yield and quality in actual production life.In contrast,the overall scores of the ripening treatment group were lower than those of the ripening treatment group after PAC spraying on walnut trees in the rapid oil transformation stage,indicating that PAC spraying is more suitable for the early stage of oil synthesis of walnut.(4)Transcriptomic mechanism of walnut fruit morphology and nutrient synthesis in response to polyphenolsThe PAC concentration(200 mg/L)with optimal effect was selected and transcriptome analysis was performed on the treated walnuts.Six major DEGs enrichment pathways were screened by gene annotation and comparative transcriptome analysis,namely: hormone signaling(ko04075,etc.),cell growth(ko00010,etc.),sugar metabolism(ko00500,etc.),flavonoid metabolism(ko00941,etc.),fatty acid metabolism(ko01212,etc.),and high temperature stress proteins(ko04141,etc.).A total of 22 differentially expressed genes were enriched to the hormone signaling pathway,14 were up-regulated and 8 were down-regulated,among which PAC treatment induced up-regulation of Delay of Germination-1(DOG1)related genes;13 differentially expressed genes were enriched to cell growth pathway,8 were upregulated and 5 were down-regulated,among which PAC treatment induced upregulation of 6 Among them,PAC treatment induced the up-regulation of 6-phosphate 1-epimerase isoform X1(GPT1);23 differentially expressed genes were enriched to the gluconeogenesis pathway,14 were up-regulated and 9 were down-regulated,among which PAC treatment induced the up-regulation of malate dehydrogenase;23 differentially expressed genes were enriched to the flavonoid metabolism pathway,14 were up-regulated and 9 were down-regulated.A total of 5 differentially expressed genes,2 up-regulated and 3 down-regulated,were enriched in the flavonoid metabolic pathway,of which PAC treatment induced up-regulated expression of cytochrome P450 98A2(CYP450)gene;14 differentially expressed genes,9 up-regulated and 5 down-regulated,were enriched in the fatty acid metabolic pathway,of which 14 days after PAC treatment at the beginning of oil synthesis induced The expression of acetylCo A carboxylase beta subunit was up-regulated 14 days after PAC treatment at the beginning of lipid synthesis;33 differentially expressed genes were enriched to the heat stress response protein pathway and all of them were up-regulated,among which 31 heat shock protein(Hsps)genes were induced by PAC treatment. |
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