Effects Of Low Temperature On Synthesis Of Flavonols And Antioxidant And Hormone Levels In Tomato Fruits

Tomato(Solanum lycopersicum L.)is one of the most widely consumed fruits and vegetables in the world.The fruit contains a large number of secondary metabolites.Flavonoids,as natural antioxidants,not only have high nutritional value,but also have important significance for the stress response of the fruit itself(Baker,1976).Facility tomato in autumn and winter often suffer cold damage during cultivation,seriously damaging the yield and quality of tomato.Moreover,in the previous study,we simulated the low temperature phenomenon of tomato planting in winter and spring by artificial climate chamber.It was clear that the flavor substances of tomato plants at different maturity stages were damaged after low temperature treatment,and the changes of fruit metabolites were different.Especially in the green maturity low temperature treatment(MGLT)is the most serious.Interestingly,the content of phenylalanine derivatives in metabolites with phenylalanine as common precursors decreased after low temperature treatment,while some flavonoids,including flavonols,accumulated at low temperatures(Wang X Y,2021).Therefore,this study preliminarily clarified the transcriptional regulation of flavonol synthesis in fruits under low temperature stress.The plants at different maturity stages were treated with low temperature(LT,18/8 ℃)until the fruit was at red maturity stage.The changes of antioxidant defense and endogenous hormone levels in tomato fruit under low temperature stress were analyzed,and the expression patterns of hormone differential genes were further analyzed by transcriptomics in order to explain the differences in fruit quality from the level of cold tolerance.The main research results are as follows:1.Screening differential transcription factors and clarifying the transcriptional regulation of flavonol accumulation at low temperature.The analysis of transcriptome data showed that the transcription factors of tomato plants at different maturity stages showed different changes after low temperature treatment,and the number of DEGs(differentially expressed genes)in ERF and WRKY families was the largest,indicating that they played an important role in the response of fruit to low temperature.The candidate transcription factor SlCBF1 was screened,and the EMSA and LUC experiments confirmed that SlCBF1 could transcriptionally activate the expression of SlFLS1,indicating that SlCBF1 transcription factor was involved in the synthesis of flavonols.2.Low temperature affected the antioxidant enzyme activity of tomato fruits at different maturity stages.The activities of POD,SOD and APX in the fruits of tomato plants at the breaker stage(BR)and pink stage(PK)were significantly increased after low temperature treatment,and the genes of antioxidant enzymes were up-regulated and a small amount of MDA was accumulated.However,there was no significant change in the antioxidant enzyme activity and gene expression in the fruits of tomato plants at green maturity after low temperature treatment,and the accumulation of MDA content in the corresponding fruits was more obvious.The results showed that tomato fruits with high maturity had higher antioxidant enzyme activity,which was beneficial to remove the accumulated reactive oxygen species in vivo and played an important role in regulating fruit cold tolerance.3.Low temperature affected endogenous hormone metabolism levels in tomato fruits at different maturity stages.BRLT and PKLT promoted the accumulation of ABA,IAA,JA and BR in tomato fruit,but MGLT decreased ABA content,and had little effect on other hormones.At the same time,low temperature treatment at each stage activated the BR signal transduction pathway and inhibited other signal pathways.Transcriptome analysis showed that BRLT and PKLT promoted the expression of ABA synthesis gene ABA2,and inhibited the expression of ABA catabolism gene CYP707 A.MGLT promoted the expression of CYP707 A,and low temperature inhibited the expression of ABA receptor.BRLT and PKLT inhibited the expression of GH3-10,which was involved in IAA catabolism,and promoted the expression of AUX1,while MGLT promoted the expression of GH3-10,and low temperature inhibited the expression of ARF,an IAA-responsive gene.Low temperature treatment at each stage significantly induced the expression of lipoxygenase LOX2 S,OPCL1 and ACX4 in JA biosynthesis genes,and inhibited the expression of JA receptor JAR1,but promoted the expression of negative regulator JAZ5.Low temperature treatment at each stage promoted the expression of BR synthetic gene DWF4/CYP90B3.At the same time,it promoted the expression of BR signal transduction genes,including BR receptor BRI1 and BAK1,BSK,BZR1/2 and TCH4,and inhibited the expression of negative regulatory factor BIN2.