Analysis Of Factors Related To Low Light-induced Tomato Pedicel Abscission

In the winter facility cultivation,Solanum lycopersicum often causes flowers and fruits abscission due to insufficient light.However,little is known about the molecular mechanism by which low light affects tomato abscission.In this paper,‘Liaoyuan Duoli' was used as a test material to control the different flower development stages of tomato to different degrees,and the effects of different low light on tomato flower pedicel abscission were determined.At the same time,the sensitivity period of tomato flower organs to light was determined,and further,through transcriptome and metabolomics analysis,the path of low light regulation of tomato detachment was revealed,which laid a foundation for clarifying the molecular mechanism of low light affecting tomato flower pedicel abscission.The main findings are as follows:1.When the fourth true leaves of tomato seedlings were unfolded,they were treated with25%,50% and 75% shading,respectively.The results showed that under 25% shading condition,the accelerated abscission was significantly accelerated,and as the degree of shading is deepened,the induced detachment rate is enhanced.,and the abscission rate is the highest under 75% shading condition.Furthermore,75% shading treatment was carried out on tomato seedlings at different flower development stages.The results showed that low light treatment significantly accelerated the abscission during the 6th to 9th stages of flower development,which was a key stage for low light regulation of tomato flower pedicel abscission.2.In order to clarify the mechanism of low light-induced tomato flower abscission,75%shading treatment was carried out at the 9th stage of flower development,and the transcriptome and metabolome were determined by abscission zone after flowering.The KEGG pathway analysis of transcriptome data revealed that differentially expressed genes were significantly enriched in photosynthesis pathways,plant hormone signaling pathways,DNA replication pathways,and secondary metabolic biosynthesis-related pathways.Among them,the differentially expressed genes in the photosynthesis pathway are concentrated in PSII and PSI,all of which are down-regulated;the differentially expressed genes in the phytohormone transduction pathway are mainly concentrated in the auxin signal transduction pathway,and the expression is down-regulated in general;the differentially expressed genes in the DNA replication pathway are all down-regulated.Expression;secondary metabolic biosynthesis related pathways mainly include phenylpropane biosynthesis pathway,flavonoid biosynthesis pathway and diterpene biosynthesis pathway,and differentially expressed genes are mainly down-regulated.Vectors for active trafficking such as the sucrose transporter(SWEET)gene and the auxin transporter gene are down-regulated.Differentially expressed genes encoding sucrose synthase are also down-regulated.At the same time,a large number of differentially expressed genes are involved in cell wall modification,cell wall synthesisgenes encoding cell wall structural proteins and cellulose synthase,and cell wall hydrolysis genes encoding extended protein and pectin esterase are mainly down-regulated.3.The results of metabolomics showed that the expression of sucrose,glucose,fructose and D-glucose-6-phosphate in tomato pedicel abscission zone was down-regulated under low light condition;the expression of indole-3-acetic acid in plant hormones was down-regulated;arginine,phenylalanine,tryptophan,histidine,tyrosine,lysine,serine and leucine accumulation in amino acid metabolism;cell wall constituents of lignin synthesis precursor trans-cinnamic acid,ethyl cinnamate,2-Hydroxycinnamic acid,(E)-p-coumaric acid is up-regulated.4.Due to the decrease of hormone content in tomato flower pedicels under low light conditions and insufficient carbon supply,it may affect the development of abscission zone.Therefore,the microstructure and ultrastructural analysis were carried out to further observe the development of the abscission zone,and it was found that the cell volume of each part of the tomato flower pedicel abscission zone was small under low light.5.Based on the above results,it is preliminarily judged that the low light-induced tomato flower pedicel abscission pattern may be: low light induces a significant decrease in tomato photosynthetic rate,which leads to inhibition of plant carbohydrate metabolism and transport,and promote competition for photosynthetic products between vegetative organs and reproductive organs;at the same time,low light inhibits the transport of auxin to the abscission zone,reduces the level of auxin in the abscission zone,and causes the imbalance of the hormone in the abscission zone to be disrupted.Sink and source competition and hormonal disorders directly induce abscission,leading to impaired development of the abscission zone,weakened secondary metabolic biosynthesis,decreased antioxidant activity,decreased stress resistance,and promoted abscission.